AFTE Glossary

Side Hammer

A firearm with the hammer located externally on the side of the frame as contrasted to an internally pivoted hammer.

Side-By-Side

A firearm with two barrels arranged adjacently in the horizontal plane.

Follower

The part in a firearm or magazine which forces a cartridge or cartridges to move through spring action.

Breech

The part of a firearm at the rear of the bore into which ammunition components are inserted.

Yoke

The part of a solid frame revolver on which the cylinder is swung out to the side to accomplish loading and ejecting. Also known as a crane.

Chamber Erosion

The wearing or physical deterioration of the chamber of a firearm caused by hot powder gases.

Stock

The wood or plastic component(s) to which the metal parts of a firearm are attached to enable the shooter to hold the firearm.

Rimfire Primer

A primer system in which the priming mixture is found in the circumferential rim cavity.

Pierced Primer

A primer that has been pierced by the firing pin during the firing process. This allows gas to flow back into the action, and can be injurious to the shooter.

Protruding Primer

A primer that has been pushed out of, or protrudes from, the primer pocket of a cartridge or shotshell after firing.

High Primer

A primer that has not been fully seated in the primer pocket and extends slightly above the head of the case. High primers can result in slam fires, particularly in semi-automatic firearms.

Thumbhole Stock

Any stock having a contoured hole in the grip area to accommodate the thumb of the trigger hand.

Target Stock

Any stock specifically made for firearms designed for target shooting.

Adjustable Trigger

Any trigger mechanism that has adjustable features.

Gunshot Residue

The total residues resulting from the discharge of a firearm. It includes both propellant and primer residues, carbonaceous material plus metallic residues from projectiles, fouling, and any lubricant associated with the bullets. Refer to the Gunshot Residue Section for various types of residue.

Finger Lever

The operating lever on lever action firearms (e.g., Winchester Model 94).

Velocity

The speed of a projectile at a given point along its trajectory.

Ramrod

A rod used to seat a load in muzzle-loading firearms.

Striker

A rod-like firing pin or a separate component which impinges on the firing pin.

Blank Stock

A rough sawed piece of wood having the approximate external outline of a stock prior to final shaping.

Orange Peel

A rough textured finish similar to the skin of an orange, generally referring to certain stock finishes.

Unload

(1) The complete removal of all ammunition from a firearm and/or magazine. (2) The disassembly of a cartridge or shotshell.

Pumpkin Ball

A round lead ball used in shotshells for hunting purposes, replaced by rifled slugs.

Cartridge Case Head Expansion

An enlargement of the head diameter upon firing.

Takedown Lever

A catch device found on many firearms to facilitate disassembly (e.g., Sauer 38H and Mauser HSc pistols). Also known as a takedown latch.

Cap

(1) An obsolete term referring to a primer. (2) Refer to Percussion Cap.

Bolt Release

A device which allows the bolt to be removed from the firearm.

Post Sight

A front sight with flat sides and top.

Reduced Charge

A less than nominal powder charge.

Resolution

In microscopy, the ability to distinguish details. Also refer to Resolving Power.

Targeting

The act of shooting a firearm to align sights. Also known as sighting in.

Proof Test

The firing of a deliberately overloaded cartridge to test the strength of a firearm barrel and/or action.

Bullet Core

The inner portion of a jacketed bullet often made of lead.

Nose

The point or tip of a bullet.

Velocity, Muzzle

The velocity of a projectile as it exits the muzzle of a firearm.

Unserviceable

A firearm which is no longer fit for firing for any reason.

Bulged Barrel

A barrel fired while containing an obstruction. The resultant excessive radial pressure causes a bulge in the barrel which may or may not be circumferential. Also known as a ringed barrel.

Duplex Cartridge

(1) A cartridge containing two projectiles with a single powder charge. (2) A cartridge containing a single projectile with two types of powder.

Buck and Ball

(1) A cartridge with a round ball and shot. (2) A load that was common for muzzleloaders.

Cartridge Case Head Separation

A 360 degree circumferential rupture of a cartridge case. Also known as cartridge case separation.

Radial Pressure Gauge

A British term denoting a gauge to measure cartridge-developed pressure through the sidewall of a cartridge case or shotshell tube as opposed to measuring the pressure transmitted through the head.

Lubaloy®

A Winchester-Western trade name for a copper bullet coating and jacketing material. When plated on lead bullets, Lubaloy does not contain zinc. When used as jacketing on composite bullets, zinc is present.

Damascus Barrel

A barrel formed by twisting or braiding together steel and iron wires or bars. The resulting cable is then wound around a mandrel and forged into a barrel tube. An obsolete barrel type. Also known as a laminated barrel.

Barrel Assembly

A barrel of a firearm, either fixed or interchangeable, that has been fitted with necessary parts so that it may be assembled to the remainder of the firearm.

Test Barrel

A barrel produced and fitted with instrumentation to measure or evaluate breech or chamber pressure, velocity, and/or accuracy.

Interchangeable Barrel

A barrel which may be readily installed on and removed from a particular action in the field.

Fluted Barrel

A barrel with longitudinal grooves cut into the outside surface for all or some portion of the overall barrel length.

Straight Pull

A bolt action firearm in which the bolt need not be rotated to open or close the action but is reciprocated by a straight backward and forward motion of the shooter's hand.

Mauser Type Bolt

A bolt action rifle design in which the bolt handle is all the way to the rear and the action cocks when opening or closing the bolt; the bolt handle does not pass through the receiver bridge.

Bore Brush

A brush usually having brass or plastic bristles which is used to clean deposits from the bore of a firearm.

Balloting (Bullet)

A bullet "ballots" when it moves through the bore of a firearm with a bumping, buffeting action. Balloting is a yawing motion of a bullet while traveling through the bore, resulting in incomplete, intermittent rifling impressions often extending onto the ogive of the bullet.

Belted Cartridge

A cartridge with a cartridge case design having an enlarged band or belt at the base ahead of the extractor groove. The belt acts as a case reinforcement and to headspace the cartridge. This construction is generally used on large capacity magnum cartridges.

Rimmed Cartridge

A cartridge with a cartridge case having a rimmed or flanged head that is larger in diameter than the body of the case. May be either rimfire or centerfire.

Bottleneck Cartridge

A cartridge with a cartridge case having distinct angular shoulder stepping down to a smaller diameter at the neck position of the case.

Crimping Groove

A circumferential groove generally of a knurled or plain appearance on a bullet or cartridge case. Three uses include securing bullets, lubrication, and identification.

Print-Through

A condition where the impressions of the lands and/or grooves in a jacketed bullet print through the jacket and can be seen on the separated lead core. May also be known as pseudo rifling.

Twelve-Twenty Burst

A dangerous situation where a 20-gauge shotshell is inserted into the chamber of a 12-gauge shotgun followed by a 12-gauge shotshell. The 20-gauge shotshell represents a serious obstruction at the forcing cone when the 12-gauge shotshell is discharged. This obstruction will produce a 'ringing' of the barrel in this area at a minimum or a bursting of the barrel in this area.

Oil Dent

A defect in a brass cartridge case, usually in the form of a shallow indentation caused by excessive oil present in dies during manufacture, in resizing dies during handloading operations, or in a chamber during firing. Also known as fluting.

Ejector, Automatic

A device found on hinge-framed firearms which expels cartridges, cartridge cases, or shotshells when the action is opened.

Drum Magazine

A drum shaped magazine in which the cartridges are arranged spirally around the central axis of the wind-up mechanism of the magazine. These were generally large-capacity magazines, being used most commonly on sub-machine guns (e.g., Thompson sub-machine gun, Luger, Russian PPSH and Degtyarov machine guns).

Matte Finish

A dull, non-reflecting surface.

Battery Cup

A flanged metallic cup used in shotshell primer assemblies that provides a rigid support for the primer cup and anvil. Also known as a battery pocket.

Cartridge Block

A flat container having blind holes into which cartridges can be inserted in an upright position to be readily available to the shooter.

Firing Pin Extension

A floating, often cylindrical, extension to the rear of the firing pin in some firearms which takes the direct impact of the hammer and transmits it to the firing pin (e.g., Astra Models 400 and 600 pistols).

Mannlicher Stock

A full length rifle stock which extends from the butt to the muzzle.

Microscopic Comparison

A general term for the comparison of two or more items under a microscope.

Cycling Marks

A general term for those toolmarks imparted onto a cartridge, cartridge case, or shotshell that has been cycled through the action of a firearm. Examples include ejector marks, extractor marks, feed ramp marks, magazine lip marks, and ejection port marks. Also known as feed marks or mechanism marks.

Pressure Curve

A graphical relationship between gas pressures in the chamber verses the time it takes the gas to exit the barrel when a cartridge is fired.

Barrel Channel

A groove in a stock or forend in which the barrel fits when the firearm is assembled.

Barrel Retainer

A grooved piece that mates with corresponding grooves on the barrels of certain firearms which serves to keep the barrels in the firearm (e.g., Czech Model P27 pistol).

Barrel, Walking

A gun barrel that changes its center-of-impact point when heated by firing.

Fulminate of Mercury

A highly explosive/corrosive component of a priming compound.

Slide Stop

A latch found on some firearms which holds the slide open. It may be either manually operated or automatically activated by an empty magazine after the last cartridge is fired. Also known as hold open latch or slide lock.

Gas Check Bullet

A lead alloy projectile with a copper or gilding metal cup pressed over the base. This metal cup is used to protect the base of the bullet from deformation due to the hot gases produced during firing.

Runaway (Gun)

A malfunctioning automatic firearm that fires multiple shots after trigger pressure is released.

Sliding Safety

A manual safety mechanism on a firearm that is operated by a sliding motion.

Yaw Card

A material such as cardstock that is selected to faithfully record the outline and orientation of a perforating projectile. Also refer to Witness Panel.

Shell Stop

A mechanical device often seen in pump action and autoloading shotguns that prevent more than one shell from feeding into the carrier, or lifter, with each cycle of the breech mechanism. Also known as cartridge stop, cut-off, or shell latch.

Cartridge Stop

A mechanical device that is employed in firearms so that only one cartridge or shotgun shell will feed into the carrier, or lifter, with each cycle of the breech mechanism. Also known as a shell latch, shell stop, or cut-off.

Machine Rest

A mechanical device that will hold a firearm in a constant position for firing even when pressure is applied to the trigger. A machine rest is typically used for testing the accuracy of ammunition or the firearm itself.

Cocking Rod

A mechanical means of cocking the hammer of some firearms.

Cocking Lever

A mechanical means of cocking the hammer or striker of some firearms using a manually operated, external lever (e.g., Sauer Model 38H pistol).

Crusher Gauge

A mechanical means of measuring and interpolating chamber pressure. This process is accomplished by subjecting a known copper or lead cylinder to the pressure developed during firing and noting the amount of compression of the cylinder that results. Also refer to Radial Pressure Gauge, Lead Units of Pressure, and Copper Units of Pressure.

Primer Cup

A metal cup (usually made of brass or copper) designed to contain priming mixture. The primer cup fits in the primer pocket or battery pocket of a cartridge or shotshell, respectively.

Stripper Clip

A metal device which may hold five to ten cartridges used to rapidly load the magazine of a pistol or rifle. In some rifles, clip guides are machined into the receiver to direct the clip into the proper position for magazine loading. The empty stripper clip may either be removed manually or ejected as the bolt closes. Also known as a charger.

Piezoelectric Gauge

A method of measuring pressure through the use of a quartz or tourmaline crystal. The quartz and tourmaline crystals will develop electric charges of opposite signs at the ends of what are called electric axes when subjected to pressure. The magnitude of the charges developed is directly proportional to the amount of pressure. Thus the output of the crystal is recorded against time and a pressure curve graph is obtained. Also known as a pressure transducer.

Offset Mount

A mount for telescopes or iron sights affixed to the gun in such a manner that the line of sight is to the side and above the receiver or barrel.

Combination Gun

A multiple barreled firearm designed to handle different sizes, calibers, or types of ammunition.

Flash Suppressor

A muzzle attachment designed to reduce muzzle flash. May also be referred to as a flash hider.

Flint Lock

A muzzleloading firearm ignition system wherein a piece of flint is secured to the hammer in such a manner as to strike steel upon hammer release. The interaction of the flint and steel causes sparks which ignite powder contained in the ignition system that subsequently ignites the main powder charge.

Breech Face Markings

A negative impression of the breech face of the firearm found on the head of the cartridge case and/or primer after firing. These impressed marks are caused by the pressures produced during firing.

Doughnut Pattern

A pattern with a central area having no pellet hits. May also be referred to as a cartwheel pattern.

Photomicrograph

A photograph taken through a microscope.

Infrared Photography

A photographic technique which can be used in gunpowder pattern tests to facilitate the viewing of smoke patterns around a bullet hole on dark pieces of clothing.

Link Pin

A pin which secures together two moveable parts.

Sidearm

A pistol or revolver.

Aiming Point

A point on the target upon which the sights are aligned.

Freebore

A portion of the barrel ahead of the chamber throat in which the rifling has been cut away, leaving the bore smooth and without a taper. Normally, use of the term freebore indicates the rifle has an unusually long throat, as is the case for most Weatherby chamberings.

Cup Wad

A powder and shot separator of very shallow cup design. When loaded with lips down, the wad acts to help seal powder gases and to protect the rear of the shot column.

Split Bridge

A receiver bridge that is cut to allow the passage of the bolt handle.

Lead Units of Pressure (L.U.P.)

A pressure value determined by means of lead crusher cylinders.

Crimped Primer

A primer cup which has been staked, stabbed, or otherwise crimped into the primer pocket. Commonly found on military cartridge cases.

Centerfire Primer

A primer system (Boxer, Berdan, or battery cup) which is assembled central to the axis of the head of the cartridge case and which is actuated by a blow to the center of its axis.

Lead Bullet

A projectile formed from a lead alloy.

Bolt Handle

A protrusion from the bolt normally at right angles to the axis of the bolt which is used to actuate the mechanism manually.

Rim, Cracked

A radial rupture of the head and rim of a shotshell or cartridge case.

Choke Tube

A replaceable insert in the muzzle of a shotgun barrel to provide the desired amount of choke.

Ring Trigger

A ring-shaped trigger.

Magazine Safety

A safety device on some semiautomatic handguns that prevents firing unless the magazine is fully inserted into the firearm.

Hammer Rebound

A safety feature of some firearms wherein spring action retracts the hammer after it has struck the firing pin.

Safety, Passive

A safety that is in place (or "on") until the trigger is pulled.

Rupture

A separation in the side wall of a cartridge case.

Flechette

A small dart multiply loaded in some shotshells and rifle cartridges used by the military.

Sling, Target

A special form of strap to aid target shooting.

Copper Clad Steel

A steel surface coated with copper by various methods, including alloying, welding, and cold-pressing.

Two-Piece Stock

A stock consisting of two separate parts - the buttstock and forearm.

Pistol Grip Stock

A stock or buttstock having a downward extension behind the trigger guard somewhat resembling the grip of a pistol. Often found on target rifles.

Backstop

A structure intended to safely stop a fired bullet or other projectile(s).

Cartridge Case Trimmer

A tool used to shorten the necks of cartridge cases that have been elongated by repeated firing and reloading.

Ballistic Table

A table of factors relating to the flight of a given projectile. Usually includes, but is not limited to, velocity and energy at various distances from the muzzle.

Smoking

A technique using the smoke from a burning magnesium strip to plate or cover a bullet or surface with toolmarks to alter its reflective properties.

Spotting Scope

A telescope used to view hits on a distant target without leaving the firing line (approximately 30X).

Bore Axis

A theoretical line through the center of the bore.

Card Wad

A thin card-like disc placed over powder or shot in shotshells. Also refer to overshot wad, undershot wad, and overpowder wad.

Drilling

A three-barreled gun in which a combination of smooth-bore and rifled barrels are used.

Rifling Broach

A tool having a series of cutting edges of slightly increasing height which is used to cut the spiral grooves in a rifled barrel, usually in a single pass.

Resizing Die

A tool used to form a cartridge case or bullet to proper dimensions. Also known as a sizing die.

Slide Drag Mark

A toolmark that occurs in a semiautomatic pistol when there is a cartridge at the top of the magazine and the slide is retracted. The lug on the underside of the slide drags across the 12 o'clock position on the cartridge case leaving a striated mark. This mark cannot occur when a cartridge is manually inserted in the chamber and the slide is released or to the first cartridge when a loaded magazine is inserted in the firearm with the slide locked back.

Slide Scuff Mark

A toolmark that occurs in a semiautomatic pistol when there is a cartridge at the top of the seated magazine and the retracted slide, either upon release or forward movement, impacts the 12 o'clock edge of the cartridge head producing a small, indented mark at this location. This mark also occurs during the normal chambering of a cartridge during the firing process. This mark cannot occur when a cartridge is manually inserted in the chamber and the slide is released.

Hinged Trigger

A trigger which is hinged to fold forward.

Cam Lock

A type of breech mechanism found on certain breechloaders, such as the 1873 Springfield. Locking on this action is accomplished by a cam located at the rear of the breechblock that fits into a mating recess.

Locking Cam

A type of lock found in certain breechloaders, such as the 1873 Springfield. Locking on this action is accomplished by a cam located at the rear of the breechblock that fits into a mating recess. This rifle is also referred to as a trap door action.

Choke, Jug

A type of shotgun choke wherein a slight recess is formed in the bore approximately one inch behind the muzzle. The recess causes the shot to gather before leaving the muzzle resulting in a denser pattern.

Single-Double Trigger

A type of trigger mechanism found on some double-barrel shotguns consisting of two triggers. The front trigger functions as a conventional non-selective single trigger, while the rear trigger will fire only the barrel with the tighter choke.

Nominal Charge

A typical charge weight of a specific powder for a specific combination of components.

Suigi Finish

A wood finish which is achieved by scorching to give a darkened and grainy appearance.

Handguard

A wooden, plastic, or metal forend/forearm that generally encircles the forward portion of the barrel to protect the shooter's hand from heat when firing.

Monocular

A word referring to a single eye (i.e., monocular eyepiece).

Maxi-Ball® Bullet

An elongated, heavy weight muzzle loading bullet usually with a large cannelure to hold lubricant. Its major diameter, being slightly larger than bore diameter, causes engraving by the rifling upon loading.

Standard Velocity

An industry term for rimfire ammunition loaded to a velocity level below high velocity ammunition of that type.

Identification

Agreement of all discernible class characteristics and sufficient agreement of a combination of individual characteristics where the extent of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool.

Cordite

An early type of smokeless, double-base propellant, distinguished by its long, cord-like shape.

Metallic Cartridge

Ammunition having a metallic cartridge case.

Match Ammunition

Ammunition made specifically for match target shooting. It is produced with special controls to assure maximum uniformity of cartridge performance.

National Match Ammunition

Ammunition produced with special care for the National Matches (at Camp Perry, Ohio) by appropriate government or commercial manufacturing facilities. Cartridges are usually, but not always, head-stamped "NM" for identification purposes.

Caseless Ammunition

Ammunition that has the propellant charge molded to the base of the bullet and not enclosed in any type of cartridge.

Barrel Step

An abrupt change in the exterior of a barrel's contour or diameter.

Pistol Grip Adapter

An accessory made to attach to the front of a revolver grip to afford a better grasp.

Laminated Cartridge Case

An area with a scaly appearance indicative of lamination caused by contamination of the brass.

Double Set Trigger

An arrangement of two triggers in which the actuation of one trigger presets the second, resulting in a lighter trigger pull of the second trigger

Firearm

An assembly of a barrel and action from which a projectile(s) is propelled by products of combustion.

Trap, Electrical

An electro-mechanical device for throwing clay targets.

Strain Gauge

An electronic device to measure stress and strain in mechanical devices.

Chronograph

An electronic instrument used to measure and record the velocities of projectiles.

Cartridge Case Life

An expression of the number of times a cartridge case can be reloaded and fired.

Berdan Primer

An ignition component consisting of a cup, explosive mixture, and covering foil. The anvil is an integral part of the cartridge case head in the bottom of the primer pocket. Generally two flash holes are drilled or pierced through the bottom of the primer pocket into the propellant cavity of the case. This system was designed by Col. Hiram Berdan. Although widely used throughout the world, this system has never been popular in the U.S., due largely to the difficulty in reloading Berdan cases.

Boxer Primer

An ignition component consisting of a cup, explosive mixture, anvil, and covering foil disc which together form the completed primer ready for assembly into the primer pocket of a cartridge case. A central flash hole is pierced through the bottom of the primer pocket into the propellant cavity of the case. Used in modern commercial centerfire ammunition made in Canada and the US.

Cam, Locking

An incline, either helical or straight, to assist in locking the action of a breech mechanism.

Safe

An incorrect, generic term for safety.

Nyclad® Bullet

An inert nylon jacketing or coating on a lead bullet; a Smith and Wesson original trade name which was purchased by Federal Cartridge Corporation.

Barrel Liner

An insert of special material placed in a barrel to reduce bore erosion, renew an eroded bore, alter bore diameter, or to strengthen the barrel..

Bullet Yaw

An instability caused by the eccentricity or imbalance of the bullet in flight. Yaw is usually the greatest in the initial portion of its flight in the atmosphere after which the bullet "goes to sleep" and becomes fully spin-stabilized. Yaw may also occur after an elongated bullet strikes an object or when it enters media other than the atmosphere. Also known as bullet tipping or bullet wobble

Helixometer

An instrument for inspecting the interior of a gun barrel and for measuring the rate of twist of the rifled bore of a firearm.

Micrometer

An instrument for making precise measurements that has a spindle moved by a finely threaded screw. It may be used in conjunction with a comparison microscope.

Manometer

An instrument for measuring gas and vapor pressure.

Trigger Puller

An instrument used to accurately measure the trigger pull of a firearm. Examples include standard weights, spring gauges, and mechanical/digital devices. Also known as a trigger tester.

Star Gauge

An instrument used to measure the inside diameter of the bore of a firearm.

Borescope

An instrument usually consisting of a tube, mirror, light source, and lens used to examine the bore and/or chamber of a firearm.

Comparison Projector

An instrument which will project a magnified image onto a screen.

Blind Box Magazine

An integral magazine having a permanently closed bottom. Loading and unloading are accomplished through the same opening.

Choke

An interior constriction at or near the muzzle end of a shotgun barrel bore for the purpose of controlling shot dispersion.

Transfer Bar

An intermediary piece of metal which usually reciprocates with the trigger or hammer of a revolver to transfer the energy of the hammer to the firing pin. When the transfer bar is not in battery with the firing pin, the hammer cannot touch the firing pin (e.g., Ruger New Model single action and double action revolvers).

Projectile

An object propelled by external force and continuing in motion by its own inertia (e.g., a bullet propelled from a firearm by the force of rapidly burning gases or other means).

Keyhole

An oblong or oval hole that is produced by an unstable bullet striking the target at an oblique angle to the bullet's longitudinal axis.

Rifling, Paradox

An obsolete barrel design in which the major length of the barrel is smooth and the last few inches are rifled.

Dumdum Bullet

An obsolete term used to describe an expanding projectile. Derives its name from bullets manufactured at the British Arsenal in Dum Dum, India around 1900.

Nitro Wad

An unlubricated, overpowder wad used with smokeless powder that is constructed of cardboard or felt. Also known as a nitro card wad or overpowder wad.

Tong Tool

An unmounted, portable handloading tool using a "nutcracker" or plier action for handloading centerfire cartridges. Also known as a nutcracker tool.

Oblique Angle

Any angle other than perpendicular or parallel.

Barrel Obstruction

Any foreign object or lodged bullet in the bore of a barrel which prevents unhindered passage of projectile(s) when fired. Also known as a bore obstruction.

Extractor Cut

Area cut in the rear of the chamber of a firearm that accommodates the extractor. Also known as Cut-out.

Neck Thickness

Average thickness of the wall of a cartridge case surrounding the bullet.

Ingalls Tables

Ballistic tables computed by Captain James M. Ingalls that were first published in 1893.

High Pressure Test Ammunition

Cartridges loaded to higher than normal pressures and used for proof testing only.

Cartridge Designation, Metric

Cartridges that are identified by their nominal bullet diameter and cartridge case length, both of which are given in millimeters (e.g., 9x19mm, 7.62x39mm, 9x18mm, etc.).

Overbore Capacity

Characteristic attributed to a cartridge with too much volume for efficient powder combustion in relationship to bore size.

Runovers/Runover Checkering

Checkering or engraving lines that extend beyond the border.

Capped Bullet

Consists of a standard lead projectile having a harder metal jacket (gilding metal, copper, etc.) over the nose. Also known as a metal point bullet.

Consecutive Matching Striae (CMS)

Contour variations within two different striated toolmarks, which, when compared microscopically, line up with one another without unexplained dissimilarities.

Barrel Corrosion

Degradation of bore and chamber surface condition due to chemical reaction.

Grooves

Depressed or cut channels in the bore of a firearm barrel to impart rotary motion to a projectile.

Bullet Stretch

Elongation of the bullet during firing.

Zwilling

European term for a double barreled shoulder arm with one rifled and one smooth-bored barrel.

Concentric Fractures

Fractures or cracks in glass or other similar brittle or ceramic material that take a generally circular form around the bullet hole or impact site in such materials.

Parabellum

From the Latin "for war." This term is typically associated with the 9mm Parabellum (9mm Luger) cartridge.

Stock Dimensions

General stock dimensions consist of the following: cast, drop at comb, drop at Monte Carlo, drop at heel, girth, length of pull and pitch.

Round Butt

Grip of a revolver with a rounded shape.

Square Butt

Handle of a revolver with a flat or squared end.

Charging Handle

Handle of semi or full automatic firearms used to cycle the firearm without firing. Also known as cocking handle, cocking knob, and operating handle

Rifling

Helical grooves cut or impressed into the bore of a firearm barrel to impart rotary motion to a projectile when fired.

Mouth Pull-Down

If a bullet is incorrectly inserted into the mouth of a cartridge case, it may deform the case mouth rearward and downward, causing a defect.

Land and Groove Impressions

Impressed areas on the bearing surface of a bullet caused by a bullet engaging with the rifling in the barrel of a firearm.

Cylinder Gap

In a revolver, the maximum space between the cylinder and the barrel. This space is typically measured with the cylinder in the rearmost position. The cylinder gap is a source of high-energy gunshot residues with unique reconstructive value. Also known as cylinder-barrel gap.

Gas

In firearms, a product of the combustion of burning gunpowder. It is the rapidly expanding gases that move the projectile through the bore of the firearm.

Breech Plug

In muzzle loading firearms, the metal piece that is threaded into the breech end of the barrel to seal the breech and usually has an integral upper tang for securing to the stock.

Small-Bore

In the United States, any firearm or ammunition of the rimfire type with a lead alloy bullet not over 0.23 inches (5.8 mm) in diameter.

Resizing

In the reloading process, the reduction in diameter of a fired cartridge case to unfired dimensions by forcing it into a die of smaller size than the fired case.

Chamber Marks

Individual microscopic marks placed upon a cartridge case by the chamber wall as a result of any or all of the following: (1) chambering, (2) expansion during firing, and/or (3) extraction.

Plinking

Informal shooting, not following any organized rules of competition or at any designated distance.

Optics

Informally, it is a general term for the components of an optical system. More precisely, the term refers to the scientific study of light and vision.

Unsuitable:

Items too damaged or in non-usable condition for examination.

Coated Bullet

Lead alloy projectile having a thin metal alloy coating. Examples include Remington® Golden™ Bullet and Winchester Lubaloy®.

Buckshot

Lead pellets ranging in size from 0.24" to 0.36" in diameter; normally loaded in shotshells.

Rifling, Polygonal

Lands and grooves having a rounded profile instead of the traditional rectangular profile. This is often seen in hammer forged barrels.

Hard Shot

Lead shot containing more than 0.5% of an alloying metal such as antimony, to increase its hardness. Also known as chilled shot.

Magazine Lip Marks

Marks produced by the lips of a magazine as the cartridges are stripped from the magazine. These thin, often curvilinear, marks are located on the body and/or rim of a cartridge case at about the 10 o'clock and 2 o'clock positions.

Class Characteristics

Measurable features of a specimen which indicate a restricted group source. They result from design factors and are determined prior to manufacture.

Gilding Metal

Metal alloys of 90% (Alloy No. 220) or 95 % (Alloy No. 210) copper and 10% or 5% zinc, respectively. Gilding metal is used extensively for the manufacture of bullet jackets. May also be known as commercial bronze.

Swivel

Metallic, elongated loops attached to rifles or shotguns through which a sling may be fastened.

Anvil Marks

Microscopic marks impressed on the forward face of the rim of a rimfire cartridge case as it is forced against the breech end of the chamber by the firing pin. These marks are characteristic of the breech under the firing pin and have been used to identify a cartridge case to a specific firearm.

Muzzle Blast

Noise that occurs during the discharge of a firearm as a result of rapid expansion of gases leaving the muzzle.

Pistol Grip

On shoulder firearms, that part of the stock behind the trigger, shaped similarly to the grip of a pistol, to afford a better grasp.

Warming Shots

Preliminary shots performed before firing for velocity, pressure, accuracy, etc.

Consecutive Striae

Parallel, side by side, contour variations within a striated toolmark.

Origin of the Trajectory

The location of the center of the bore of a firearm at that specific point in time when the bullet exits the barrel.

Trace Evidence

Physical evidence of a microscopic or submicroscopic size which, due to its small size, is deposited on or transferred to one or more objects without being manifestly apparent at the time of transfer or deposition.

Bore Casting

Pouring a special material that has exceptional dimensional stability into the bore or chamber of a firearm in order to make a cast for the study of its physical characteristics.

Safety (Handling)

Precautions taken by firearms users to help provide protection against accidental or unintentional discharge.

Bedding

Refers to the fit or the fitting of the parts of the barrel and receiver with the stock.

Base, Low

Refers to the height of a relatively low internal base wad within a shotshell.

Base, High

Refers to the height of a relatively tall internal base wad within a shotshell.

Barrel Life

Refers to the total number of rounds that have been fired in a barrel or the total number of rounds fired in a barrel before it becomes unserviceable.

Trigger

That part of a firearm mechanism that is moved manually to cause the firearm to discharge.

Rifling Marks

Rifling impressions on the surface of a fired bullet. Also known as bullet engraving.

Bullet Engraving

Rifling impressions seen on the surface of a fired bullet

Gain Twist Rifling

Rifling in which the rate of twist (pitch) of the lands and grooves increases as it approaches the muzzle.

Steel Shot

Soft steel pellets made specifically for use in shotshells.

Side Screw

Screw used to attach side-locks to frame and/or stock.

Screw Plug

Screw used to fill holes for sight or telescope (sight) mounting when not in use. Also used to fill access holes to internal pins. Also known as a dummy screw.

Elimination:

Significant disagreement of discernible class characteristics and/or individual characteristics.

Bolt Face

That part of the breechblock or breech bolt which is against the head of the cartridge case or shotshell during feeding and firing. Also known as breech face.

Breech Face

That part of the breechblock or breech bolt which locks against the rear of the chamber, and is against the head of the cartridge case or shotshell during firing.

Receiver Ring

That part of the receiver on bolt action rifles into which the barrel is fitted.

Operating Lever

That part operated by the hand to open and close the breech of a lever action firearm.

Bearing Surface

That portion of a bullet's outer surface that comes into direct contact with the interior surface of the barrel. Also known as the band.

Top Strap

That portion of a solid frame revolver which passes over the cylinder.

Small-of-the-Stock

That portion of the stock between the rear of the action and the comb which has the smallest circumference.

Window

That area in the frame of a revolver into which the cylinder fits.

Objective

That lens or lenses in an optical instrument which form the image of an object.

Magazine Well

That opening in a firearm which receives a detachable magazine.

Glass Bedding

The application of a mixture of fiberglass and resin between the action and/or barrel and stock.

Port, Loading

The opening in a receiver where a cartridge may be placed in the firearm either directly into the chamber or the magazine.

Average Pressure

The arithmetic mean of a number of cartridges tested for pressure.

Head

The base of the cartridge case which contains the primer and is the location of the headstamp.

Cartridge Case Head

The base of the cartridge case which contains the primer.

Integral Base Wad

The base wad incorporated into the body of a plastic shotshell. May be referred to as a unibody shell.

Receiver

The basic unit of a firearm which houses the firing and breech mechanism and to which the barrel and stock are assembled. In revolver, pistols, and break-open firearms, it is called the frame.

Bullet Blackening

The black discoloration of the bullet incidental to firing.

Relief Engraving

The carving of raised scenes that produces three-dimensional figures.

Cartridge Case Length

The dimension of a cartridge case from the face of the head to the mouth of the cartridge case.

Neck Clearance

The dimensional difference between the diameter of the neck of a loaded cartridge case and the chamber.

Dram Equivalent

The accepted method of correlating relative velocities of shotshells loaded with smokeless propellant to shotshells loaded with black powder. The reference black powder load chosen was a 3 dram charge of black powder with 1 1/8 oz. of shot and a velocity of 1200 fps. Therefore, a 3 dram equivalent load using smokeless powder would be with 1 1/8 oz. of shot having a velocity of 1200 fps or 1 1/4 oz. of shot and a velocity of 1165 fps. A 3 1/4 dram equivalent load might have 1 1/8 oz. of shot and a velocity of 1255 fps.

Slam Fire

The accidental discharge of a firearm upon closing of the action which may be due to one of the following:- A firing pin that has stuck and failed to retract.- A primer that is either inadequately seated or overly sensitive. - A weak or broken firing pin retaining spring which fails to overcome the inertia of motion imparted to the firing pin during closure, thereby allowing the firing pin to strike the primer with sufficient force to cause discharge. - A firearm with inadequate headspace.

Aim

The act of aligning the sights of a firearm on a target.

Target Shooting

The act of shooting at inanimate objects. "Formal" target shooting is done at specified distances at targets designated for scoring. "Informal" target shooting is done at varying distances at impromptu targets for practice. This informal target shooting is also known as plinking.

Bullet Stabilization

The act of steadying a bullet in flight by use of the proper rifling twist and bullet velocity.

Toe

The bottom (lower) end of a buttplate and adjacent portion of the stock on a shoulder firearm.

Floor Plate

The bottom of a box magazine. The plate may be hinged, sliding, or immovable.

Barrel Catch

The catch on hinged frame firearms that locks the barrel in the closed position (e.g., Smith & Wesson New Departure, Beretta 950B and Stevens Tip Up pistols).

Center of Impact

The center of a shot pattern or target made by a series of projectiles fired at the same aiming point.

Cratering

The characteristic cone shape on the exit side of a projectile hole through a relatively brittle medium (e.g., glass, bone, etc.) caused by the spalling around the exit. Also known as coning effect.

Coning Effect

The characteristic cone shape on the exit side of a projectile hole through a relatively brittle medium (e.g., glass, bone, etc.) caused by the spalling around the exit. Also known as cratering.

Ejection Pattern

The charting of where a particular firearm ejects fired cartridge cases or shotshells.

Locking Block

The component in a firearm designed so that when the action is closed, a block(s) slide into place securing the bolt in the locked position. Also known as locking bolt.

Battery

The condition in a firearm action in which the bolt or breechblock is solidly secured in a fixed relationship with the chamber so as to resist being blown back by chamber pressure.

Bolt Throw

The degrees of rotation required to open the bolt

Penetration

The depth that a bullet or shot pellet will travel into a target medium.

BB

The designation of spherical shot having a diameter of .180" used in shotshell loads. The term BB is also used to designate steel or lead air gun shot of .175" diameter. Although the two definitions cause some confusion, they have co-existed for many years.

Group Measurement

The determination of the center distance between two bullet holes farthest apart in a target. This is referred to as the "group extreme spread." Other common measurements made are the extreme horizontal and vertical spread and the mean radius.

Reconstruction

The determination of the sequence of two or more events in a particular incident utilizing information derived from the physical evidence.

Drift

The deviation in flight of a bullet from the center line of the bore due to the gyrational spin of the bullet imparted by the rifling.

Magazine Release

The device that retains or releases the magazine in a firearm. Also known as magazine catch, magazine latch, or magazine lock.

Shot Spread

The diameter of a shot pattern.

Rifling Twist

The direction (right or left) and rate at which the rifling of the firearm turns within the bore. This is normally expressed as the distance required for the rifling (and projectile) to make one complete revolution. Depending on the origin of the firearm, this may be written in inches or in millimeters (e.g., 1 turn in 12 inches or 1 turn in 305 mm).

Twist

The direction of turn of the rifling helix, such as left hand or right hand twist.

Black Powder

The earliest form of propellant, reputed to have been made by the Chinese or Hindus before the remote beginnings of history. First used for guns in the 13th century. It is a mechanical mixture of potassium or sodium nitrate ("saltpeter"), charcoal, and sulfur with the most common proportions being 75:15:10. For sporting arm use, various granulations are available. These are designated fg, ffg, fffg, and ffffg, largest to smallest, respectively

Cartridge Case Stretching

The elongation of the body of a cartridge case during firing.

Physical Match

The examination of two or more objects through physical, optical, or photographic means, where the examiner determines whether the objects were either one entity or were once held or bonded together in a unique arrangement.

Primer Pellet

The explosive component of a primer.

Backstrap

The exposed metal strip at the rear of a pistol or revolver grip.

Primer Flow-Back

The extrusion of the primer into the firing pin aperture. This phenomenon can produce identifiable marks.

Barrel Straightening

The factory straightening or re-straightening of a barrel to remove bends induced during machining operations.

Water Table

The flat portion of the frame on break-open firearms which extends forward from and is approximately at right angles to the standing breech face. This is the surface on which barrel flats rest when the gun is closed. May also be referred to as action bar flats.

Tipping

The flight characteristics of a projectile resulting in its entering the target at an angle to its trajectory characterized by an oblong or oval hole in a target. Also known as keyhole.

Bow Effect

The flow pattern of abrasive materials in soil, sod and/or sand around the nose, ogive and/or bearing surface of a bullet generated during penetration into and ricochet from such materials. This characteristic pattern is uniquely associated with ricochets from soil, sand or sod that have yielded to the bullet's impact and allowed the bullet to enter into the substrate to some depth before departing the substrate. It is most noticeable on the ogive of the bullet, but may extend back along the bearing surface as well. This type of marking takes its name from the similarity of the flow pattern of water off the bow of a boat.

Wad Pressure

The force applied to a wad column as it is sealed firmly against the propellant.

Pressure

The force developed in a firearm by the expanding gases generated by the combustion of the propellant.

Derringer

The generic term applied to many variations of small one-, two- or even four-shot pistols, using both percussion caps and cartridges.

Case Taper

The gradual reduction in diameter of a cartridge case from head to shoulder or mouth.

Maximum Charge

The greatest charge weight, in grains, of a particular propellant that may be used with specified ammunition components without exceeding the safe, maximum, allowable pressure limit for the specific cartridge or shotshell being loaded.

Length of Stock

The greatest dimension of the stock material. Applies to both rifles and shotguns.

Maximum Range

The greatest distance a projectile can travel when fired at the optimum angle of elevation of the barrel. Also known as extreme range.

Best Known Non-matching Agreement in Toolmarks

The greatest individual corresponding agreement between two toolmarks known to have been created by different tools that has either been personally observed by trained examiners or has been observed by others in the profession by rigorous studies.

Primer Flash

The high temperature illumination produced by the extremely hot gases which result from the rapid build-up of pressure and temperature when the priming mixture detonates.

Peak Pressure

The highest value that the chamber pressure reaches during the burning of propellant.

Firing Pin Aperture

The hole in the breech face of a firearm through which the firing pin protrudes.

Muzzle Flash

The illumination that occurs during firing which is the result of the expanding gases from the burning propellant particles emerging from the barrel behind the projectile and uniting with oxygen in the air.

Firing Pin Impression

The indentation of the primer of a centerfire cartridge case or in the rim of a rimfire cartridge case caused when it is struck by the firing pin. May also be referred to as a firing pin indent.

Trigger Takeup

The initial distance the trigger moves prior to sear movement. Also known as pretravel and trigger slack.

Primer Seating

The insertion of a centerfire primer or battery cup in the head of a cartridge case or shotshell. Properly seated, it should be flush or below the face of the head.

Bore

The interior of a barrel forward of the chamber.

Hammer Spur

The knob or extension of an exposed hammer which acts as a cocking/decocking aid.

Spur Hammer

The knob or extension on an exposed hammer which acts as a cocking or decocking aid.

Receiver Axle

The large pin which secures the rear toggle link to the breech bolt on Luger pistols.

Cast

The lateral displacement of the centerline of the buttplate (pad) from the centerline of the bore. For a right-handed shooter, when the centerline of the buttplate is to the left of the bore, it is expressed as cast-on and to the right as cast-off. The opposite is true for left-handed shooters. Applies to both rifles and shotguns.

Bolt

The locking and cartridge head support mechanism of a firearm that operates in line with the axis of the bore. Also known as the breech bolt. In revolvers, bolt is sometimes used to refer to the cylinder stop.

Seating Depth

The longitudinal position of a bullet or primer in a cartridge case or a wad in a shotshell.

Temperature of Ignition

The lowest temperature to which the surface of material must be raised for the combustion of the material to become self-sustaining.

Bullet Diameter

The maximum dimension across the largest cylindrical section of a bullet.

Effective Range

The maximum distance at which a projectile can be expected to be useful in its intended purpose.

Mainspring

The mechanical energy storage device which operates the striker or hammer of a firearm.

Frizzen

The metal arm of a muzzleloader's lock that serves as a striking plate and guides sparks into the pan. When not in use, the frizzen also protects unfired priming power in the pan.

Grip Frame

The metal structures that form the grip on certain handguns, especially where the grip is removable, such as Colt single action revolvers.

Underbolt

The moveable lock of some break-open firearms. It typically engages the barrel lug (underlug) and is actuated by the top lever.

Bullet Creep

The movement of a bullet out of the cartridge case as other cartridges are being fired. This phenomenon is due to the recoil of the firearm and the inertia of the bullet. Also known as bullet starting and popping.

Barrel Whip

The periodic movement of the barrel as the projectile passes through it.

Center Pin

The pin around which the cylinder of a revolver rotates. Also known as axis pin, base pin, and cylinder pin.

Point of Aim

The place or point on a target which intersects the straight line generated by the alignment of the front and rear sight of a firearm.

Cylinder Frame

The portion of a single action revolver which houses the cylinder, hammer, and trigger group; distinguished from the grip frame (e.g., Ruger Single-Six revolver).

Sprue Cutter

The portion of the mold which removes the sprue in the casting process.

Half Cock

The position of the hammer of a firearm when about half retracted and held by the sear, intended to prevent release of the hammer without normal pull of the trigger.

Full-Cock

The position of the hammer or striker when the firearm is ready to fire, excluding double action only firearms.

Distance Determination

The process of determining the distance from the firearm, usually the muzzle, to the target based upon patterns of gunpowder or gunshot residues deposited upon that target. Where multiple projectiles, such as shot, have been fired, the spread of those projectiles is also indicative of distance.

Bore Slugging

The process of driving a piece of lead through the bore of a rifled barrel to determine the minimum bore and groove diameters.

Ejection

The process of expelling a cartridge, cartridge case, or shotshell from a firearm.

Casting

The process of pouring a liquid or suspension into a mold to produce an object of desired shape.

Land

The raised portion between the grooves in a rifled barrel.

Point Blank Range

The range to which a shooter can obtain a hit in the vital zone of a particular target or game animal, while the sights are correctly aligned on the target.

Cyclic Rate

The rate at which a succession of movements repeats itself. In an automatic firearm, it is usually expressed in shots per minute that are theoretically possible to be fired, given an unlimited supply of ammunition.

Speed of Rotation (Spin)

The rate of spin of a projectile fired from a rifled barrel.

Firing Pin Retaining Plate

The removable plate at the rear of the slide on some pistols which holds in the firing pin. The rebounding firing pin has spring tension pushing it to the rear causing the rear of the firing pin to protrude through a hole in the retaining plate. This keeps the plate in position and allows the rear of the firing pin to be struck by the hammer (e.g., U.S. 1911 pistol).

Restock

The replacement of one stock with another.

Rebarrel

The replacing of a barrel with another barrel.

Cast

The reproduction of a toolmark or the surface of a tool utilizing a molding material such as plaster of Paris, silicone rubber, etc. The cast of a toolmark is a positive case. The cast of the surface of a tool is a negative cast.

Annulus

The ring-like space between the top of the primer and the primer pocket or battery cup in the base of the cartridge.

Ballistics

The science of projectiles in motion. Usually divided into three parts: 1) Interior Ballistics, which studies the projectile's movement inside the firearm; 2) Exterior Ballistics, which studies the projectile's movement between the muzzle and the target; and 3) Terminal Ballistics, which studies the effect of a projectile's impact at the target. A term often confused with Forensic Firearms Identification.

Screw, Tang

The screw or screws passing through either one or both tangs by which the stock or trigger guard is attached to the receiver or frame.

Tang Screw

The screw or screws passing through either one or both tangs by which the stock or trigger guard is attached to the receiver or frame.

Base Pin Screw

The screw that retains the base pin or cylinder pin. Found on revolvers like the early Colt "Frontier" revolvers.

Far Zero

The second point where the bullet path intersects with the line of sight, or where the point of aim and point of impact coincide.

Projectile Rotation

The spinning motion that is imparted to a projectile due to engagement with the rifling in the barrel of a firearm, as it is driven down the barrel. The rate of rotation is dependent upon the rate of twist of the rifling and the velocity of the projectile. The barrel twist (left or right) determines the direction of the rotation.

Magazine Spring

The spring in a magazine that exerts tension against the follower.

Recoil Spring

The spring which returns a semiautomatic or automatic firearm to battery. Also known as an operating spring, retracting spring, or closing spring.

Crack Rule

The stopping of the propagation of one or more radial fractures during a projectile's impact in plate glass or other similar material by a fracture from a previous shot.

Explosion

The sudden release of a sufficient amount of energy to create a pressure wave. The energy to produce an explosion may come from a variety of sources including nuclear energy, pressure, or chemical reaction. Pressure related explosions include a rapid change in state (i.e., liquid to gas) or the over pressurization of a container (i.e., the failure of a gas cylinder). A chemical explosion is an event in which a quantity of matter is instantaneously converted to gaseous product with the generation of high temperature and pressure.

Inertia

The tendency of an object at rest to remain at rest or of an object in motion to remain in motion in a straight line unless acted upon by an external force.

Semi-Finished Stock

The term for a stock which has been rough shaped and partially or completely inletted.

Hammer Fall

The travel of the hammer from the full cock position to the fully forward position.

Oil Proof

The treatment of a cartridge case to minimize the entry of oil or water.

Cylinder Axle

The tubular piece upon which the cylinder rotates (e.g., Enfield revolver No. 2).

Stock Warpage

The twisting and bending of a wood stock due to moisture absorption.

Speed of Sound

The velocity at which sound travels through air. The velocity can be affected by conditions such as air temperature, altitude, barometric pressure, and relative humidity, but at standard sea level conditions is approximately 1115 feet per second.

Velocity, Striking

The velocity of a projectile upon impact.

Fiber Optics

Thin, transparent fibers of glass or plastic which transmit light throughout their length by internal reflections that are typically enclosed by an opaque material.

Ricochet Angle

This angle is defined by the path taken by the ricocheted projectile (or major projectile fragments) as it departs the impacted surface.

Blowback, Simple

This system, in its simplest form, allows for a totally unlocked breech and relies simply on the mass of the breechblock and the strength of the return spring to prevent the cartridge case from emerging from the chamber during its period of peak pressure (e.g., 22 rimfire semiautomatic rifles or pistols).

Stoppage

This term is used when a firearm stops firing due to a malfunction of either the gun mechanism or ammunition. This term is normally used in connection with automatic firearms, machine guns, etc.

Implode

To burst inward.

Discharge

To cause a firearm to fire.

Swage

To form metal under pressure. Swaging is normally performed in a press, using a punch or die.

Double-Barrel

Two barrels in a firearm mounted to one frame. May be vertically (over-under) or horizontally (side-by-side) aligned.

Doubling

Unintentional firing of a second shot that typically occurs through a malfunction of the firearm.

Blow, Light

Used to describe insufficient firing pin energy or protrusion. The result is erratic ignition or failure to ignite the primer.

Doll's Head

Usually a round extension of the top of the barrel or rib of a shotgun which fits into a matching hole in the top of the standing breech.

Contour Variation

Variations in the elevations of the ridges and valleys in striated marks and of forms and shapes or depressions in impression marks.

Shot Cup

Various designs of cup-shaped plastic inserts in shotshells which hold shot pellets and reduce their deformation during barrel travel.

Macroscopic

Visible to the unaided eye (or up to 10X magnification).

Filler Wad

Wads of various shapes (typically circular) and various thicknesses used to adjust the volume of the contents of a shotshell. These disks may be constructed of various materials such as paper, cardboard, fiber, or plastic..

Annular Rim

circular rim at the rear of the cartridge containing a primer compound.

Antimony (Sb)

metallic element used to alloy lead in order to increase hardness.

Fire-Forming

the process of changing the original, external shape of a cartridge case to the shape of the chamber through the firing process. The caliber of the cartridge case must be dimensionally similar to the caliber of the firearm. This process can be engineered or unintentional depending on the circumstances.

Heel

(1) The part of a rifle or shotgun stock at the top of the butt end. (2) The rear portion of a bullet, or its base.

Cut-Out

(1) The portion of the slide or bolt which has been cast, formed, machined, or drilled out to permit the operation of the extractor. (2) A hole or slot formed through the breech face of a firearm to permit the operation of the ejector.

Base

(1) The rear portion of a bullet that is opposite the nose. Also known as the heel (2) That portion of a cartridge case which contains the primer (more commonly known as the head) or the filler material which constitutes the lowest or base wad in a shotshell.

Web

(1) The solid portion of a brass centerfire cartridge case between the inside of the case at the head end, and the bottom of the primer pocket. (2) This word also refers to the smallest dimension of a smokeless powder granule.

Forcing Cone

(1) The tapered section at the front end of a shotgun chamber by which the diameter of the front end of the chamber is reduced to bore diameter. (2) The tapered section towards the muzzle end of a shotgun barrel that gradually reduces in size from bore diameter to choke diameter. (3) The tapered entrance to the bore at the breech end of a revolver barrel.

Take Down

(1) To disassemble a firearm for cleaning, repair, or transportation. Also known as stripping or field stripping. (2) A type of firearm designed for ease of disassembly and transportation.

Cock

(1) To place a firing mechanism (hammer, firing pin, or striker) in a position for firing. (2) A firearm part that holds pyrite or flint; the predecessor of the hammer.

Known Non-matching Toolmarks

(1) Toolmarks known to have been made by different tools. (2) Toolmarks produced by the same tool but deliberately placed in a non-matching position.

Blowback

(1)In ammunition, a leakage of gas rearward between the case and the chamber wall from the mouth of the case. (2)In firearms, a design found in semiautomatic and automatic firearms where the weight of the bolt, the inertia of some component, and/or a mechanical delay is the main locking force and no mechanical locking of the breech occurs. These firearms directly utilize the breech pressure exerted on the head of the cartridge case to actuate the mechanism.

Flattened Primer

1) A condition in which the normally round perimeter of a fired primer cup is squared off due to internal pressure. 2) A primer cup configuration in which the normally domed crown is flattened to improve sensitivity.

Theory of Identification as it Relates to Toolmarks

1. The theory of identification as it pertains to the comparison of toolmarks enables opinions of common origin to be made when the unique surface contours of two toolmarks are in "sufficient agreement." 2. This "sufficient agreement" is related to the significant duplication of random toolmarks as evidenced by the correspondence of a pattern or combination of patterns of surface contours. Significance is determined by the comparative examination of two or more sets of surface contour patterns comprised of individual peaks, ridges and furrows. Specifically, the relative height or depth, width, curvature and spatial relationship of the individual peaks, ridges and furrows within one set of surface contours are defined and compared to the corresponding features in the second set of surface contours. Agreement is significant when the agreement in individual characteristics exceeds the best agreement demonstrated between toolmarks known to have been produced by different tools and is consistent with agreement demonstrated by toolmarks known to have been produced by the same tool. The statement that "sufficient agreement" exists between two toolmarks means that the agreement of individual characteristics is of a quantity and quality that the likelihood another tool could have made the mark is so remote as to be considered a practical impossibility. 3. Currently the interpretation of individualization/identification is subjective in nature, founded on scientific principles and based on the examiner's training and experience.

Powder Scale

A balance or weighing instrument for accurately weighing powder charges or other ammunition components.

Squeeze Bore

A barrel design in which fired bullets having a spool-like body are squeezed to a smaller diameter in passing from the breech to the muzzle. The idea of this firearm was to present a large cross-sectional area of the projectile to the propellant gases and to present a small cross-sectional area to the atmosphere in order to reduce air resistance and thus increase the muzzle velocity of the projectile. Also known as a Gerlich type gun, a taper bore gun, or a reducing bore gun.

Five-In-One Blank

A blank cartridge that was designed for use in firearms of different calibers. It can be used in caliber 38-40, 44-40, and 45 Colt revolvers and in caliber 38-40 and 44-40 rifles. Also known as a movie blank.

Recoil Lug

A block or plate on the bottom of the receiver and/or barrel to help absorb some of the recoil to the stock and prevent splitting of same.

Mannlicher Type Bolt

A bolt action rifle design in which the receiver bridge has a gap at the top to permit passage of the bolt handle. In this type of action, the bolt handle also serves as a locking lug (e.g., Mannlicher-Schoenauer and Italian Carcano rifles and carbines).

Stock Bolt

A bolt which passes through a buttstock lengthwise to secure it to the receiver or frame.

Staggered Box Magazine

A box magazine having two zigzagged columns of cartridges. This increases the capacity without lengthening the magazine. Also known as a double stack magazine (e.g., Browning Hi-Power and S&W Model 59).

Armor Piercing Bullet

A bullet consisting of a hardened core or wholly composed of a substance other than lead or lead alloy.

Test Bullet

A bullet fired into a bullet recovery system in a laboratory for comparison or analysis.

Jacketed Hollow Point Bullet

A bullet having a metal jacket enclosing a lead alloy core. The entire bullet is enclosed except for the nose, which has a cavity.

Bevel Base Bullet

A bullet possessing a beveled edge at its heel. This feature assists the seating of such bullets in the cartridge case at the time of manufacture or during a reloading process.

Keyholed Bullet

A bullet that strikes or enters a medium in a yawed or destabilized orientation.

Steel Jacketed Bullet

A bullet with a jacket made of steel.

Recoil Pad

A butt plate, usually of rubber, to reduce the sensible recoil of shoulder firearms.

Trigger Stud

A button-type trigger mechanism in which the end of which is pressed to fire the firearm.

Stud Trigger

A button-type trigger, the end of which is pressed to fire the firearm.

Skeleton Stock

A buttstock which is usually metallic without material in the center so that the weight is reduced.

Test Cartridge Case

A cartridge case obtained while test firing a firearm in a laboratory to be used for comparison or analysis.

Triplex Cartridge

A cartridge containing three projectiles.

Short

A cartridge designation that generally has a shorter cartridge case than others in the same caliber (e.g., 22 short versus 22 long or 22 long rifle).

Short Round

A cartridge in which the bullet is seated below the specified minimum length.

Blank Cartridge

A cartridge loaded without a projectile that is designed to produce a loud noise.

Fixed Ammunition

A cartridge or shotgun shell comprised of a case, primer, propellant powder, and projectile(s).

Squib Load

A cartridge or shotshell which produces substantially lower than normal projectile velocity and/or sound and which may result in the projectile and/or wads remaining in the bore. Also known as a squib or squib discharge.

Subcaliber Ammunition

A cartridge that is smaller than standard for the firearm in which it is used, utilizing a subcaliber device.

Express Cartridge

A cartridge that produces greater than standard velocity. The name was derived from cartridges developed in England around 1885.

Tapered Cartridge

A cartridge with a cartridge case in which the diameter is gradually reduced from head to shoulder or mouth.

Blank

A cartridge without a projectile designed to make noise. Blanks may also be used to launch rifle grenades.

Long Gun

A category of firearms with relatively long barrels that includes rifles

Rebated Cartridge

A centerfire cartridge having a cartridge case whose rim diameter is smaller than the diameter of the body of the case.

Semi-Rimmed Cartridge

A centerfire cartridge with a cartridge case having a case head only slightly larger in diameter than the body with an extractor groove just forward of the head.

Rimless Cartridge

A centerfire cartridge with a cartridge case whose case head is of approximately the same diameter as the body, having a groove forward of the head to provide an extraction surface.

Shot Cartridge

A centerfire or rimfire cartridge loaded with small diameter shot. Designed to be fired in firearms other than a shotgun (e.g., CCI 22LR shotshell).

Shot Cartridge

A centerfire or rimfire cartridge loaded with small diameter shot. Ex. CCI 38/357 Shotshells

Chamber, Fluted

A chamber that has grooves cut in the chamber wall to assist or retard cartridge case extraction (e.g., Russian Tokarev semiautomatic rifle and the Heckler and Koch model HK4 pistol).

Chamber, Roughened

A chamber with walls that are deliberately roughened in a variety of ways to slow down or delay extraction (e.g., 30 Carbine caliber Kimball semiautomatic pistol).

Work Hardened

A change in the grain structure of a metal as a result of repeatedly stressing it. In cartridge cases, work hardening most frequently occurs in and around the neck area, from the stresses of repeated firings and resizing. This causes brittleness and leads to cracking and splitting of the case.

Mainspring Housing

A channel in which the mainspring rides (e.g., US 1911 pistol).

Target, Clay

A circular, domed, frangible disc used as an aerial target for shotgun shooting games. Originally formed out of clay, modern "clay" targets are generally made from a formulation of pitch and limestone. Dimensions and weights are regulated by skeet and trap shooter's associations. Also called clay bird or clay pigeon.

Cannelure

A circumferential groove generally of a knurled or plain appearance on a bullet or cartridge case. Three uses include crimping, lubrication, and identification.

Grease Groove

A circumferential groove, or cannelure, on a bullet generally of a knurled or plain appearance which is designed to hold lubricant.

Split Rim

A circumferential rupture of the rim of a cartridge or shotshell.

Rim, Split

A circumferential rupture of the rim of a shotshell or cartridge case.

Slotted Tip

A cleaning rod tip with a slot to hold a cleaning patch.

En Bloc Clip

A clip that holds cartridges either in a single column or in two staggered columns. The clip is inserted directly into the magazine well of certain firearms and is necessary for the firearm to function. The clip is ejected after the last cartridge is fired (e.g., U.S. M1 Garand rifles and Italian Carcano rifles and carbines).

Ammunition Code Number

A code number and/or letter(s) usually found on the carton that identifies a particular quantity of ammunition for its manufacturer.

Known Standards

A collection and cataloging of both cartridges and ammunition components utilized by the firearm examiner; may include both unfired and fired ammunition components. Also known as reference ammunition or fired standards.

Ammunition Standards(1)

A collection and cataloging of both cartridges and ammunition components utilized by the firearm examiner; may include both unfired and fired ammunition components. Also known as reference ammunition, fired standards, or known standards. (2) Ammunition used by test ranges to evaluate test barrels, ranges, and other velocity and pressure measuring equipment. May also be used as a control sample by which other characteristics are compared, such as accuracy, patterns, etc. Also known as reference ammunition.

Fired Standards

A collection and cataloging of test fired bullets, cartridge cases, and shotshells from known firearms. Also known as known standards, ammunition standards, or reference ammunition.

Firearms Reference Library

A collection of firearms maintained by a laboratory for the following reasons: -To identify the make, model, and source of evidence firearms. -To provide exemplar firearms for various testing purposes which otherwise compromise evidence firearms. -To provide an exemplar resource for training new examiners or in developing new technology for the examination of firearms. -To provide a source of firearms parts for the repair of evidence firearms for test firing purposes. -To provide a resource for the identification of firearms parts recovered at crime scenes. -To provide a resource for the location and style of firearms serial numbers.

Jam

A colloquial term referring to the malfunction of a firearm that prevents the action from operating; may be caused by faulty parts, ammunition, improper maintenance, or improper use of the firearm.

Silencer

A colloquial term used to describe a device attached to the barrel of a firearm designed to reduce the noise of discharge. Such a device is more accurately identified as a sound suppressor.

Percussion Composition

A combination of chemical ingredients that will explode when struck sharply with sufficient energy.

Priming Mixture

A combination of explosive and/or pyrotechnic chemical ingredients which explode or deflagrate from the impact of a firing pin. The priming mixture is pressed into a cup or spun into the rim cavity of a rimfire cartridge.

Pistol, Automatic

A common but improperly used term applied to autoloading pistols in use today. Most current "automatic" pistols are semiautomatic in action only.

NATO Cartridge

A common designation for military cartridges produced under the specifications of the North Atlantic Treaty Organization (NATO). A common designation for 9mm and 7.62 mm NATO military cartridges.

Assault Rifle

A compact, select-fire, detachable box magazine-fed firearm, that utilizes a centerfire rifle cartridge and is designed primarily for military use.

Reloading Tables

A compilation of data suggesting combinations of various components suitable for reloading a given caliber or gauge. These data are usually referred to as reloading data.

Shotshell, Plastic

A complete round of ammunition having a plastic body, a base wad that may or may not be a single unit, and a metallic head.

Bolt Sleeve

A component at the rear end of the bolt which guides the firing pin and supports the firing pin spring in bolt action rifles. Also known as bolt plug.

Dog, Carrier

A component in certain repeating action firearms which engages or is attached to the carrier or lifter and acts to control its motion. Also known as the lifter pawl.

Bridge

A component of a firearm action which usually straddles other parts and acts as a guide or support (e.g., receiver bridge, Model 98 Mauser).

Extractor

A component of a firearm which is designed to remove the cartridge, cartridge case, or shotshell from the chamber of the firearm.

Antimony Sulfide (Sb2S3)

A component of most common priming mixtures that serves as a fuel.

Barium Nitrate

A component of most priming mixtures which acts as an oxidizer of the particular fuel in such mixtures.

Calcium Silicide

A component of some priming mixtures that serves as a fuel.

Hammer

A component of the firing mechanism which strikes the firing pin or primer.

Stirrup

A component with divided legs to apply force equally. It is mainly used in trigger assemblies where it is necessary to straddle another component.

Jar Off

A condition in which a firearm may fire if dropped or jarred when the safety is off. This phenomenon occurs without the trigger being pulled. Testing for this condition involves placing the safety in the "off" position and dropping the firearm from approximately waist height onto a hard surface to see if it will fire. Testing for this condition may also be referred to as drop testing. Also refer to Drop Fire.

Secondary Explosive Effect (S.E.E.)

A condition that can occur when slow-burning tubular powders are used at greatly reduced charge weights in large capacity bottle necked cartridges. Rather than burning in a normal fashion, the powder detonates, as though it were a severe overload. Also known as a high pressure excursion.

Conoidal Bullet

A cone shaped projectile. Also known as a conical bullet.

Minié Ball Bullet

A conical nosed lead bullet, slightly under bore diameter, incorporating a hollow base, designed to expand into the rifled bore upon firing for gas sealing purposes without the use of a patch.

Trigger Bar

A connecting piece between the trigger and the sear.

Rim Seat

A counterbore in the rear end of a chamber or bolt face to support the head of a rimmed cartridge.

Muzzle Cap

A cover on the muzzle end of a barrel to keep out foreign matter.

Dust Cover

A cover over the magazine opening and/or ejection port of a firearm to prevent the entrance of foreign matter into the action.

Spall

A crater formed from chipped or fragmented material as a result of projectile impact in brittle or frangible materials such as concrete, cinder blocks, sheetrock, etc. It more often describes such a crater on the exit side of a bullet impact site, but the term has also been used to describe an impact crater in otherwise hard materials.

Offset Stock

A curved buttstock for use by a shooter who wishes to use the left eye when shooting right handed or vice versa. Also known as a cross-over stock.

Chamber Reamer

A cutting tool used to form the chamber area of a barrel bore or revolver cylinder. Reaming is typically performed in two steps using a rough reamer and a finish reamer.

Primer Pocket

A cylindrical cavity formed in the head of a metallic centerfire cartridge case, or in the head of a shotshell, to receive an appropriate primer, or battery cup primer assembly.

Base Wad

A cylindrical component that is assembled into the head end of a shotshell.

Base Wad

A cylindrical component that is assembled into the head of a shotshell.

Pellet, Cup

A cylindrical cup-shaped pellet used in air rifles and pistols.

Hinge Pin

A cylindrical part, in hinged frame guns, on which the barrel(s) pivots. Also called a joint pin.

Gas Piston

A cylindrical piece which is housed in the gas cylinder or gas tube of some gas operated firearms which is directly impinged upon by gas from the gas port in the barrel. It is this piston which is driven rearward that moves the breechblock and ejects the cartridge case and then feeds a cartridge into the chamber (e.g., US M1 and US M14).

Blish Lock

A delayed blowback breech lock designed by John Bell Blish, Commander, USNR in 1915. This system incorporated a phosphor bronze "H" shaped piece that rode in slots within the actuator and bolt on Thompson sub-machine guns. The purpose of this piece was to absorb the force produced by the gases, and due to the difference in angles, the piece was forced upwards and only slightly back. The theory was that the greater the force, the more the "H" piece jammed. The dissimilar metals were supposed to adhere while under pressure. At lower pressures, it moved freely to allow rearward movement of the bolt

Blossoming

A deposit of white or yellow powder, usually forming around the juncture of a barrel and its receiver, on a newly blued firearm. It is caused by incomplete rinsing after bluing and can be removed by wiping off with a rag and then oiling the juncture. Also known as efflorescence.

Mushroom/Mushrooming

A descriptive term for a soft point, hollow point, or special type of bullet point that expanded upon impact with a target, as designed. Bullets of this design are meant to increase sectional diameter with a minimum weight loss and release of all of the bullet's kinetic energy within the target, resulting in a mushroom shape.

Blow-Forward Action

A design for semiautomatic or automatic firearms wherein the breech block is stationary and the barrel moves forward by gas pressure to open and eject the cartridge and cycle the action.

Rolling Block Action

A design in which a breechblock and hammer each rotate about their separate transverse pins in the receiver. The two members are swung rearward, away from the barrel breech to load the mechanism, or extract a cartridge case. To fire a cartridge, the breechblock is closed and locking is accomplished by the falling hammer engaging an abutment on the breechblock (e.g., Remington No. 4 and Winchester model 1887).

Sidelock Action

A design in which the firing mechanism is attached to a sideplate rather than being integral with the frame.

Box Lock Action

A design in which the hammer and hammer spring(s) are located within the frame and the trigger assembly is located in the lower tang. Generally found on double barrel shotguns such as Parker, Fox, Stevens, Winchester Models 21 and 24, etc.

Truncated Cone Bullet

A design of flat-nosed projectile having a conical rather than rounded profile.

Soft Point Bullet

A design providing for exposure of a portion of the core at the nose of a jacketed projectile.

Hybrid Action

A design that incorporates aspects of both single action and double action systems. For example, a pistol action which requires the slide to retract and set or partially cock the action, and the trigger to further cock and release the hammer or striker.

Hinged Frame Action

A design wherein the barrel(s) is pivoted on the frame. When the action is open, the barrel(s) may pivot up, down, or sideways for loading or unloading. When the action is closed, the breech of the barrel(s) swings against the standing breech. Opening is normally accomplished by movement of a top-, side-, or under-lever.

Lever Action

A design wherein the breech mechanism is cycled by an external lever generally below the receiver.

Muzzle Brake

A device attached to or integral with the muzzle end of the barrel that uses propelling gases to reduce recoil. Also known as a compensator.

Compensator

A device attached to or integral with the muzzle end of the barrel that uses propelling gases to reduce recoil. Also known as muzzle brake.

Calipers

A device consisting of two moveable legs or jaws used to measure diameter, thickness, or distance between two surfaces.

Loading Block

A device containing a number of blind holes into which cases or completed ammunition are placed.

Shell Catcher

A device for catching fired cartridge cases. May also be commercially known as Brass Catcher.

Matchlock

A device for igniting gunpowder developed in the fifteenth century, a major advance in the manufacture of small arms. The matchlock was the first mechanical firing device. It consisted of an S-shaped arm, called a serpentine, that held a match, and a trigger device that lowered the serpentine so that the lighted match would fire the priming powder in the pan attached to the side of the barrel.

Recoil Pendulum

A device for measuring free recoil energy in which a firearm is suspended from fixed points so as to allow it to swing freely while the barrel remains horizontal.

Lock Frame

A device incorporated into the mechanism of some firearms where the barrel and bolt assembly recoil upon firing. The lock frame acts to absorb the shock of the recoiling parts prior to the bolt unlocking and opening.

Disconnector

A device intended to disengage the sear from the trigger. In a semiautomatic firearm it is intended to prevent full automatic firing. In a manually operated firearm, it is intended to prevent firing without pulling the trigger.

Safety Mechanism

A device on a firearm intended to help provide protection against accidental discharge under normal usage when properly engaged. Such a mechanism is considered "on" when the position of the safety device is set in a manner to provide protection against accidental discharge under normal usage. Such a mechanism is considered "off" when it is set to allow the firearm to be discharged by a normal pull of the trigger. A manual safety is one that must be manually engaged and subsequently disengaged to permit normal firing. An automatic safety is one that goes to the "on" position when the action of the gun is opened. A passive safety is in place (or "on") until the trigger is pulled. An example would be the transfer bar system in some revolvers.

Grip Adapter

A device that alters the size or shape of the handle portion of a pistol or revolver. Generally used when a handgun is used for target practice.

Muzzle Booster

A device that can be affixed to the muzzle end of a firearm barrel. When the firearm is fired, the gases following the bullet down the bore expand into the chamber of the device and exert a backward force on the barrel face, accelerating the rearward movement of the barrel and the breech locked to it. Some primary applications of this principle are machine guns, pistol suppressors, and blank firing adaptors. Also known as a recoil intensifier.

Telescope Mount

A device to hold a telescope on a firearm. Frequently abbreviated as scope mount.

Lever Lock

A device to hold the lever closed on lever action firearms.

Firing Pin Stop

A device to limit the forward motion of the firing pin thus preventing pierced primers.

Cylinder Stop

A device to stop cylinder rotation in proper alignment with the barrel of a revolver. Also known as cylinder bolt.

Cylinder Bolt

A device to stop cylinder rotation in proper alignment with the barrel. Also known as a cylinder stop.

Rest

A device to support a firearm during firing.

Bolt Catch

A device typically found on rifles which lock the bolt in the open position.

Headspace Gauge

A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also known as a breeching plug.

Adapter

A device used to alter the use or function of a firearm. The most general use of an adapter permits using smaller caliber ammunition in a firearm designed for a larger caliber. May also be referred to as an auxiliary cartridge, auxiliary chamber, or subcaliber device.

Pressure Transducer

A device which generates an electrical charge that is proportional to the pressure applied to its crystal element. Also refered to as a Piezoelectric Gauge.

Transducer, Piezoelectric Pressure

A device which generates an electrical charge that is proportional to the pressure applied to its crystal element. This device may be used by ammunition and firearm manufacturers in proof testing barrels and ammunition.

Cylinder Latch

A device which permits the swinging out or release of the cylinder from the frame of a revolver. Also known as cylinder release latch or bolt.

Bolt Stop

A device which retains the bolt in the firearm during normal operation.

Checkering

A diamond-like pattern in wood, plastic, or metal components of a firearm for improving grip or ornamentation.

Extractor Cam

A disc shaped piece with a hook on its outer diameter which pivots on the joint pivot screw and impinges directly on the extractor post to push out the extractor when opening top break revolvers (e.g., Smith & Wesson New Departure).

Out of Battery Discharge

A discharge that takes place when the firearm's locking mechanism is not fully closed. Unlike a slam-fire, an out of battery firing is normally the result of the shooter intentionally pulling the trigger. Upon firing, the unsupported case may rupture and vent gasses back into the action. This is a very hazardous situation for the shooter, and can damage or destroy the firearm. Also known as premature firing.

Firearms Identification

A discipline of forensic science which has as its primary concern to determine if a bullet, cartridge case, or other ammunition component was fired by a particular firearm.

Cape Gun

A double barreled shoulder arm with barrels side-by-side; one being smoothbore and the other being rifled.

Slot Blank

A dovetail-shaped metal part to occupy an unused dovetail slot.

Stem (Stemming)

A failure of a cartridge to feed, in which the cartridge jams against the top or bottom of the chamber.

Fail To Fire

A failure of the firearm to discharge after the trigger has been pulled. Also refer to Misfire.

Misfire

A failure of the priming mixture to be initiated after the primer has been struck an adequate blow by a firing pin, or the failure of the initiated primer to ignite the powder.

Stove-Pipe

A failure to eject in which the cartridge case is caught in the ejection port by the forward motion of the bolt or slide.

Wad

A felt, paper, cardboard, or plastic component used in a shotshell for various purposes.

Open Case Ammunition File

A file containing bullets and/or cartridge cases recovered from unsolved crimes wherein a firearm was discharged but not recovered. Also known by a variety of terms in various laboratories and agencies which maintain them, (e.g., open case bullet file, open case file, open shooting file, or unsolved case file).

Cartridge Guide

A firearm component which acts as a guide for the cartridge while it is being fed from the magazine to the chamber. Also known as cartridge lifter.

Side Lock

A firearm design in which the firing mechanism is attached to a detachable side plate rather than being integral with the frame.

Machine Gun

A firearm design that feeds rifle cartridges, fires, extracts and ejects cartridge cases as long as the trigger is fully depressed and there are cartridges in the feed system. Actuation of the mechanism may be from an internal power source such as gas pressure or recoil, or external power source, such as electricity. Also called fully automatic or full auto

Handgun

A firearm designed to be held and fired with one hand.

Target Hammer

A firearm hammer having a wider spur designed for convenient and rapid cocking.

Hammerless

A firearm having no hammer or having a concealed hammer.

Inertia Trigger

A firearm having two barrels and a single selective trigger wherein the inertia resulting from the recoil forces of firing one barrel causes the trigger sear to switch to the unfired barrel.

Bolt Action

A firearm in which the breech closure is in line with the bore at all times, manually reciprocates to load, unload, and cock, and is locked in place by breech bolt lugs and engaging abutments, usually in the receiver.

Sporting Gun

A firearm intended primarily for sport and recreation.

In Battery

A firearm is said to be "in battery" when the breeching mechanism is in the proper position for firing.

Out of Battery

A firearm is said to be "out of battery" when the breeching mechanism is not in proper position for firing.

Short Recoil Operation

A firearm mechanism (action) in which the breechblock remains locked to the barrel only while the pressure is high. This involves a barrel travel of only about ½ inch. The device locking the breechblock to the barrel is then released and the two components separate. The barrel may remain stationary and await the return of the breechblock, but in most modern designs, the barrel has its own spring and goes forward into battery.

Semi-Inletted Stock

A firearm stock that has been shaped partially so that the barreled action fits into the wood and requires additional hand fitting to achieve a proper fit. Also known as a rough inletted stock.

Hinged Frame

A firearm with a frame that is hinged to facilitate loading and ejection. Generally, the barrel(s) pivots downward.

Rifle

A firearm with a rifled bore designed to be fired from the shoulder.

Smooth Bore

A firearm with an unrifled bore.

Musket

A firearm with long barrel and forend or forearm extending nearly to the muzzle.

Single Shot Action

A firearm with no means in the mechanism for storing or loading more than a single cartridge housed in the chamber of the barrel.

Over And Under

A firearm with two barrels, one placed over the other.

Revolver

A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis. The firearm is discharged successively by the same firing mechanism.

Revolver Action

A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis. The firearm is discharged successively by the same firing mechanism.

Blanked Primer

A fired primer cup in which the firing pin impression has been punched out by internal gas pressure. A potentially dangerous situation, normally indicating excessively high pressures, but is not unique to this cause.

Spent Projectile

A fired projectile which has lost all of its kinetic energy.

Rimfire Cartridge

A flange-headed cartridge containing the priming mixture inside the rim cavity.

Rimfire

A flange-headed cartridge containing the priming mixture inside the rim cavity. Often used to refer to 22 caliber ammunition, the most common current rimfire caliber.

Trigger Lock

A form of firearm safety which blocks trigger movement. This is designed to be engaged while the firearm is in storage and it should not be applied to a loaded firearm. This is not a typical part of a firearm.

Rifling, Gain Twist

A form of rifling where the twist rate (pitch) increases towards the muzzle.

Slug, Brenneke

A formed, rifled slug having either a wad assembly attached to its base by a screw or a pressed on plastic wad that is intended for use in shotguns.

Brenneke Slug

A formed, rifled slug used in shotguns with a wad assembly either pressed into or attached to its base by a screw.

One Piece Stock

A full length stock made from a single piece of wood. Includes both the butt and forend.

Rifle, Automatic

A fully automatic shoulder firearm that starts firing when the trigger is pulled and continues until the trigger is released, a malfunction occurs, or ammunition is exhausted. The term should not be used in conjunction with semiautomatic firearms.

Muzzle Imprint

A general term describing the marks produced by the muzzle, front sight, magazine tube, spring housing, etc., and caused by the contact discharge of a firearm.

Barrel Lug

A general term for any projection extending at right angles to the barrel. One of several types of projections located on the underside of the barrel or barrels on hinged frame firearms which serves to secure the barrel to the action or receiver, is used for locking, and aids in barrel positioning in the frame. Also known as lumps.

Lock

A general term referring to the total firing mechanism of a firearm. The action, either manual or automatic, of locking or supporting the bolt of a firearm immediately prior to firing.

Bird Shot

A general term used to indicate any shot smaller than buckshot.

Wadcutter Bullet

A generally cylindrical projectile design having a sharp, shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring.

Metallic Ammunition

A generic term for rimfire and centerfire ammunition which have metallic cases.

Micrometer, Stage

A glass microscope slide bearing a scale in the center of the slide that is 1 or 2 mm long, subdivided into tenths and hundredths of a millimeter or tenths, hundredths, and thousandths of an inch.

Ballistic Soap

A glycerin-type soap specially designed to simulate muscle tissue for use in wound ballistics studies of projectile behavior. The most common studies involve penetration depth and projectile deformation or expansion.

Air Gun

A gun that uses compressed air or gas (carbon dioxide) to propel a projectile. The majority of projectiles in the U.S. are 17 to 22 caliber and are either round or cup-shaped lead "pellets", however larger caliber air rifles are being manufactured (up to 50 caliber), which are used for hunting and competition. True air guns should not be confused with guns that use spring force to propel projectiles (commonly known as BB guns). Also known as an air rifle, pellet rifle, or pellet gun.

Martini Action

A hammerless, single shot rifle mechanism, lever actuated, in which the movement of the breechblock is entirely within the receiver and pivots at the rear.

Grip, Bird's Head

A handgun grip that comes to a point at the lower front making it somewhat resemble a bird's head.

Pistol

A handgun in which the chamber is integral with the barrel.

Double Action

A handgun mechanism in which a single pull of the trigger first cocks and then releases the hammer or striker.

Pistol, Air

A handgun with the same principle of operation as an air gun. Also known as a pellet pistol.

Steel Penetrator

A hardened steel component within a jacketed bullet that is designed to improve penetration in "hard" targets.

Receiver, Universal

A heavy duty mechanical device into which chambered barrels are secured for testing ammunition.

Trap Door Buttplate

A hinged closure plate in the rear end of a firearm. Opening of the trap door exposes a recess in the stock which can be used for storage.

Nipple

A hollow, cone shaped part of a percussion firearm upon which a percussion cap is placed. When fired, the flame, or flash, from the percussion cap passes through a hole in the nipple and into the chamber to ignite the powder charge.

Holster Stock

A holster usually made of wood which attaches to the rear of the pistol grip of certain handguns and serves as a shoulder stock (e.g., Browning Hi-Power and Mauser "Broomhandle" pistols).

Step Base Bullet

A jacketed bullet having a small, flat recess or 'step' in its base.

Steel Core Bullet

A jacketed projectile containing a core that is usually composed of mild steel.

Barrel Nut

A large nut which fits over the barrel, engages a shoulder on the barrel, and threads into the receiver to hold the barrel in place. Examples are on the Savage 110 and on the German MP40 sub-machine gun.

Plated Bullet

A lead core or jacketed bullet that has been covered with a different metallic material. Electrolysis is the typical method used for plating bullets.

Outside Lubricated Bullet

A lead projectile lubricated on the surface not covered by the cartridge case.

Thumb Rest

A ledge in the grip area of a rifle or handgun on which to rest the thumb of the trigger hand.

Achromatic Lens

A lens made up of a combination of glasses having different focal powers so that the image formed is free of unwanted colors.

Rebound Lever

A lever found in Colt revolvers which is actuated by the mainspring and serves to control the motion of the bolt (cylinder stop) and trigger.

Under Lever

A lever found on some hinged frame guns which is located on the bottom of the receiver. When the lever is moved to the unlocked position, it allows the barrel(s) to pivot for loading or unloading.

Slide Lock Safety

A lever mechanism found on some semiautomatic handguns which serves as a slide lock and a safety mechanism (e.g., Colt 32 and 380 pistols).

Witness Mark

A line on each of two mating parts which must be an extension of each other when assembled to indicate proper alignment. Also known as a draw line or an index mark.

Axis of Bore

A line through the center of the bore.

Joint

A location where two or more parts come together.

Safety, Automatic

A locking device on some firearms designed to return to the "on" (safe) position when the action of the firearm is opened.

Rotating Barrel

A locking system in which the barrel, slide, and receiver are locked together by helically cut lugs. When the firearm is fired, the lugs cause the barrel to rotate, freeing the slide to move rearward (e.g., 9mm Steyr M12 pistol (Steyr-Hahn)).

Through Bolt

A long bolt extending through the shoulder stock and threaded into the frame.

Shotgun

A long gun designed to shoot from the shoulder, typically having a smooth bore and designed to fire shotshells.

Operating Rod

A long rod extending from the gas piston which may be attached to a charging handle.

Neck Crack

A longitudinal defect in a cartridge case neck that may occur with repeated reloading. It is a result of the metal stretching during firing, followed by diameter reduction during resizing in a die (cold working). Neck cracks may also occur due to the aging of the brass in cartridges that have been stored for many years, particularly if in a corrosive atmosphere. Also refer to Split Neck.

Split Neck

A longitudinal rupture in the neck of a metallic cartridge case.

Cartridge Case Split

A longitudinal rupture in the side wall of a cartridge case or shotshell. Also known as cartridge case rupture.

Split Shoulder

A longitudinal rupture in the side wall of the shoulder of a bottleneck cartridge case.

Split Case

A longitudinal rupture in the wall of a cartridge case or shotshell.

Draw Mark

A longitudinal scratch on a cartridge case caused by foreign material on either the draw punch or die during fabrication.

Split Base

A longitudinal split in the sidewall of the brass or steel cup assembled on a plastic or paper shotshell.

Keeper

A loop or clip made of leather, metal, or plastic used as a means of holding straps or cords, such as gun slings, together.

CB Cap

A low velocity 22 caliber rimfire cartridge having a conical bullet (from which the name is derived) and no propellant other than the priming compound.

Flash Suppressant

A material that is added to the propellant for the purpose of reducing muzzle flash.

Tarage Table

A mathematical table which correlates the amount of compression of a copper or lead crusher to the chamber pressure testing firearm.

Forearm, Anson Fastening

A means of attachment for the forearm of double barreled shotguns which utilizes a bolt that extends beyond the tip of the forearm. Pressure on the protruding stud or button allows removal of the forearm.

Percussion

A means of ignition of a propellant charge by mechanical blow against the primer or percussion cap.

Bullet Trap

A means of safely stopping a bullet in flight when recovery is not the objective. Usually incorporates a steel plate set at an angle to deflect the bullet up or down into a pit or receptacle.

Filar Micrometer

A measuring device fitted to the eyepiece of an optical instrument for measuring small distances.

Vernier Caliper

A measuring instrument having a fixed jaw, a sliding jaw, and a point that slides along an attached scale.

Reloading Press

A mechanical device for hand loading cartridges or shotshells.

Ejector

A mechanical device of a firearm which expels a cartridge, cartridge case, or shotshell.

Trap, Mechanical

A mechanically operated device for throwing clay targets.

Loaded Chamber Indicator

A mechanism on a firearm that reveals when a cartridge is chambered if the firearm is in battery. May take the form of a small rod, raised extractor, or other mechanism that protrudes or raises to indicated a loaded status. A small opening in the chamber can also function as a chamber indicator (e.g., Ruger LC9, Beretta PX4 Storm, Smith & Wesson Sigma Series, etc.).

Breech Bolt

A mechanism that operates in line with the axis of the bore which locks and unlocks the breech of a firearm; typically also functions to chamber a cartridge in semiautomatic and automatic firearms.

Ballistic Gelatin

A medium designed to simulate living soft tissue for use in wound ballistics studies of projectile behavior. The most common studies involve penetration depth and projectile deformation or expansion.

Slide

A member attached to and reciprocating with the breechblock.

Action Bar

A member or members designed to have considerable rigidity, which are used to connect and thus transmit the movement of the forearm or gas system to the breechblock. In many designs, the movement of the action bar(s) controls or actuates other parts of the mechanism.

Skeleton Butt Plate

A metal buttplate forming only a border for the butt.

Investment Casting

A metal forming technique that can produce complex shapes or parts with little or no additional finishing. In precision casting a ceramic mold is produced by surrounding or investing an expendable pattern with a refractory slurry. Once the slurry has dried, the mold is placed in a furnace or autoclave to melt/and or vaporize the expendable pattern (made of wax, plastic, or frozen mercury). The mold is then filled with casting metal. After cooling, the shell is removed by hammering or through the use of a vibratory machine. Ruger and Thompson Center use this process. Also known as the lost wax process or precision casting.

Lock Plate

A metal plate mounted on the stock of a firearm to provide for mounting of, or access to, the firing mechanism.

Barrel Extension

A metal projection which extends rearward from the breech end of the barrel into which the breech locks while the firearm is in battery or firing position (e.g., Remington, Model 870).

Mandrel

A metal rod or bar used as a core around which metal, wire, etc. is cast, molded, forged, or shaped.

Butt Plate

A metal, rubber, or composition covering to reinforce and protect the shoulder end of a firearm stock.

Magazine Throat

A metallic insert found in some plastic magazines which aligns the next cartridge to be fed into the chamber (e.g., Ruger 10/22 carbine).

Sling Swivel

A metallic loop to which the sling is attached.

Friction Ring

A metallic ring surrounding the magazine tube to slow the rate of recoil allowing for safe ejection of the shotshell and subsequent feeding of the next cartridges (e.g., Browning Auto-5 shotgun).

Drop Test Primer

A method of determining the sensitivity of primed cases. The primed cases are held in a specified die and subjected to a range of specified firing pin blows imparted by a freely falling ball.

Ammunition Color Code

A method of distinguishing the various gauges of shotshells and types of metallic ammunition by color or plating.

Striker Fire

A method of firing which involves the striker being held by a spring until released by the sear.

Mean Radius

A method used to measure ammunition and/or firearm accuracy capability. To determine the mean radius, the center of the group is located and the distance to the center of each shot from the group center is measured and recorded. The sum of these measurements is then divided by the number of shots

Micrometer, Eyepiece

A microscope eyepiece (ocular) with a permanently mounted micrometer scale engraved on the glass and permanently mounted in the plane of the diaphragm.

Round

A military term for a cartridge.

Quadrant Elevation

A military term for the elevation of the muzzle of the firearm above the horizontal plane, usually expressed in mils.

Alloy

A mixture of two or more metals fused or melted together to form a new material. For example, brass is an alloy composed of copper and zinc.

Deep Hole Drilling

A modern technique for barrel drilling involving rotation of the blank on a non-rotating bit, under high pressure lubrication. The drill bit itself is asymmetrical, cutting one side only. The hole is usually drilled about 5 thousands of an inch under the size of the bore diameter. A reamer is then used to bring the hole up in size, leaving a fine finish and a hole of uniform diameter from end to end.

Latch

A moveable device used to secure a part or piece in place relative to another. As applied to firearms, various types of latches are employed to hold barrels, cylinders, etc. in position during firing and to enable these parts to be moved for loading and unloading.

Parkerizing

A non-reflecting, rust-resistant finish used on metal surfaces of some firearms. Also known as phosphatizing or phosphate coating.

Killing Power

A non-scientific term for the lethality of a bullet.

Twin-Single Trigger

A non-selective, double trigger arrangement used on some double-barrel firearms. The barrels are fired sequentially with each pull of one or both triggers.

Bullet

A non-spherical projectile for use in a rifled barrel.

Lump, Hook of

A notch machined into a lump used to mate with the hinge pin.

Sear Notch

A notch typically located in the hammer, in which the sear or trigger is held under tension of the mainspring until released by movement of the trigger. Also known as the bent.

Bent

A notch typically located in the hammer, in which the sear or trigger is held under tension of the mainspring until released by movement of the trigger. Also known as the sear notch.

Ratchet

A notched wheel on the rear of a revolver cylinder which causes the cylinder to rotate when force is applied by a lever called a hand.

Serial Number

A number applied to a firearm for identification purposes. The Gun Control Act of 1968 requires all firearms manufactured after 1968 to bear a unique serial number.

Trigger Group

A number of components within the firearm assembly that work together to release the hammer/striker when the trigger is pulled. Also known as a trigger assembly or trigger mechanism.

Shot Size

A numerical or letter(s) designation indicating the average diameter of a pellet.

Quantitative Consecutive Matching Striae Identification Criteria

A numerical standard used when making a quantitative assessment of CMS in a comparison of a test striated toolmark with a questioned striated toolmark. The amount of CMS is compared to an empirically determined numerical threshold which is greater than the best known non-matching (KNM) quantitative CMS value. When the best KNM value is exceeded, a positive toolmark identification can be made with confidence.

Quantitative Consecutive Matching Striae

A numerical tabulation of CMS runs. Typically, the number of CMS is designated by a number, followed by the letter x (e.g., 2x, 3x, etc.).

Coefficient of Form

A numerical term indicating the general profile of a projectile.

Combination Wad

A one piece plastic wad which combines the function of some or all of the following: shot protector, filler wad, and overpowder wad.

Trip

A part of the mechanism of some firearms which is released by the action of the trigger.

Link Assembly

A part or assembly which joins two parts together and transfers motion from one part to another (e.g., Winchester 1873 and US 1911 pistol).

Link

A part that connects two other parts while permitting flexibility between the parts.

Sear

A part which retains the hammer or striker in the cocked position until the trigger is pulled.

Pellet, Skirted

A pellet designed for use in air or CO2 rifles, pistols, or revolvers with a round or flat nose and a flared base. Also known as a waisted pellet.

Cap and Ball

A phrase used to describe a muzzleloading firearm using the percussion cap ignition system.

Practical Impossibility

A phrase, which currently cannot be expressed in mathematical terms, that describes an event that has an extremely small probability of occurring in theory, but which empirical testing and experience has shown will not occur. In the context of firearm and toolmark identification, "practical impossibility" means that based on 1) extensive empirical research and validation studies, and 2) the cumulative results of training and casework examinations that have either been performed, peer reviewed, or published in peer-reviewed forensic journals, no firearms or tools other than those identified in any particular case will be found that produce marks exhibiting sufficient agreement for identification.

Hammer Shroud

A piece added to or a portion of the frame of a revolver to cover the sides of the hammer.

Grip Pin

A pin installed in the frame of some handguns to position the grips.

Slave Pin

A pin used during assembly of a firearm to facilitate the process and later replaced by a permanent pin or screw.

Starter Pistol

A pistol or revolver designed to fire blanks which may be used to sound the start of sporting events. These firearms are designed so they cannot fire bullets.

Pressure Gauge

A piston and crusher system or a piezoelectric transducer system used to measure internal chamber and/or barrel pressure in a firearm or test device.

Pawl

A pivoted or hinged part used to cause unidirectional motion over a definite distance or angle of rotation. Also known as a dog or hand.

Overpowder Wad

A plastic or fiber spacing disk positioned immediately over the powder charge in a shotshell to separate the propellant from other components within the shotshell.

Shot Collar

A plastic or paper insert surrounding the shot charge in a shotshell which aids in keeping the shot compact, reducing the shot pattern. The collar also assists with cutting down flattening or deformation of shot/pellets during barrel travel. Also known as a shot sleeve.

Bridle

A plate found in some firearm mechanisms that holds tumblers, sears, and pins in their proper relationships.

Mounting Stage

A platform on a microscope on which the object is positioned for viewing.

Loading Ramp

A platform or cut in the bottom of the receiver of some single shot firearms that aids in guiding a cartridge into the chamber as the action in closed. This term is not synonymous with the feed ramp.

Nipple Pick

A pointed instrument used to clean the orifice of nipples on percussion firearms.

Ball Screw

A pointed, spiral piece of metal secured at the end of a ramrod and used to remove a lead ball or patch from a muzzle loading gun. Also known as a ball or bullet puller.

Blown Primer

A primer that is separated completely from the cartridge or shotshell after firing due to severe expansion of the primer pocket and head.

Dropped Primer

A primer that is separated completely from the cartridge or shotshell after firing without obvious distortion of the primer pocket and head. Also refer to Blown Primer.

Non-Mercuric Primer

A primer which contains no fulminate of mercury or other mercuric compound in its priming mixture. A mercuric primer may or may not be corrosive, depending on whether or not it contains potassium chlorate.

Non-Corrosive Primer

A primer which does not contain chemical compounds that could produce corrosion or rust in gun barrels.

Loose Primer

A primer which does not fit properly in the primer pocket of a cartridge case or shotshell.

Electric Primer

A primer which is ignited by electricity instead of impact from a firing pin. Ex. Remington Model 700 ETRONX Bolt Action Rifle uses cartridges with an electric primer (R-P 22-250 REM).

Corrosive Primer

A priming mixture that contained compounds of chlorine and oxygen, generally used in military ammunition made before 1952. The residues are hygroscopic (retain moisture) and therefore promote bore rusting.

Pressure Estimation

A procedure for establishing pressure of a cartridge by visual observation or fired cartridge case measurements. Not an accurate method for determining pressure.

Bullet Casting

A process for making lead bullets by pouring molten metal into a mold.

Incendiary Bullet

A projectile containing a chemical compound which ignites upon impact with the intended purpose of starting fires.

Exploding Bullet

A projectile containing an explosive material designed to detonate upon impact.

Spitzer Bullet

A projectile design having a sharp pointed nose, a long ogive, and sometimes a boattail base.

Partition Bullet

A projectile designed for controlled expansion that has a jacket divided into two chambers which encloses the forward and rear cores of the bullet. It is designed so that the first chamber expands and the rear chamber holds together for penetration.

Frangible Bullet

A projectile designed to disintegrate upon impact with a hard surface in order to minimize ricochet. Sometimes referred to as a disintegrating bullet or gallery bullet.

Expanding Bullet

A projectile designed to increase in diameter upon impact. Examples include hollow point and soft point bullets.

Pointed Bullet

A projectile designed with a pointed profile.

Cast Bullet

A projectile formed by pouring molten lead or lead alloy into a mold.

Metal Cased Hollow Point Bullet

A projectile having a metal jacket enclosing a lead alloy core. The entire bullet is enclosed except for the cavity in the nose. Refer Hollow Point Bullet.

Jacketed Bullet

A projectile having an inner core typically enveloped by a metallic substance.

Inside Lubricated Bullet

A projectile having cannelures containing lubrication which are covered when seated in the cartridge case.

Full Metal Jacket Bullet

A projectile in which the bullet jacket encloses the entire bullet, with the usual exception of the base. Also called full jacketed, full patch, full metal case, metal cased, metal patched, and ball ammunition.

Total Metal Jacket Bullet

A projectile made by copper plating a lead core to create a jacket that encloses the entire bullet. The jacket is much thicker than cosmetic copper plating.

Wax Bullet

A projectile made from paraffin and/or other wax preparations, usually used for short range indoor target shooting.

Wooden Bullet

A projectile made of hollow wood which will disintegrate in the bore or a short distance from the muzzle.

Ogive, Secant

A projectile nose with the curvature not tangent to the cylindrical bearing portion.

Tracer Bullet

A projectile that has a burning compound in its base which permits observation of its flight.

Swaged Bullet

A projectile that has been shaped by compressing and forming the bullet material in a die.

Mushroomed Bullet

A projectile that has expanded upon impact to a mushroom-like shape.

Hollow Point Bullet

A projectile with a cavity in the nose to facilitate expansion.

Spire Point Bullet

A projectile with a conical nose profile.

Hollow Base Bullet

A projectile with a deep base cavity.

Semi-wadcutter Bullet

A projectile with a distinct, short truncated cone on a cylindrical body with sharp shoulders. Like the wadcutter bullet, it is intended to cut target paper cleanly but does not have the feeding issues that may be experienced with a wadcutter bullet.

Flat-nosed Bullet

A projectile with a flattened tip at right angles to its axis.

Round Nose Bullet

A projectile with a hemispherical nose.

Semi-jacketed Hollow Point Bullet

A projectile with a partial jacket and exposed lead nose with a cavity.

Semi-jacketed Bullet

A projectile with a partial jacket and exposed lead nose.

Steady Pin

A projection at the end of a mainspring which fits into the lock plate of a side lock action gun.

Lumps, Bifurcated

A projection on the underside of a barrel(s) found mainly on expensive over/under shotguns. The bifurcated or divided lumps are mounted on each side of the lower barrel, as opposed to under it, which serves to reduce the overall height of the receiver-barrel assembly.

Lump, Chopper

A projection on the underside of a barrel(s) which is integral with the barrel.

Top Extension

A projection which extends behind the breech end of the barrels on some break open firearms. When the firearm is closed, it fits into a corresponding recess slot in the frame and is used for locking purposes.

Long

A proper name given to some cartridges to differentiate them from others of the same caliber.

Snap Cap

A protective device to permit dry firing without damage to the firing pin.

Cheekpiece

A raised portion on the side of the buttstock of a long gun where the shooter rests his cheek when aiming.

Rib, Ventilated

A raised sighting surface which is separated from the barrel by means of posts that allow air to circulate around it. Its purpose is to eliminate heat waves in the line of sight. Also known as a bridge rib.

Rib

A raised surface used as a sighting plane that may either be solid or ventilated.

Axis

A real or an imaginary straight reference line passing through an object and about which the object turns or appears to turn.

Open Sight

A rear sight having a notch through which the front sight is aligned for aiming.

Tang

A rearward projecting tongue on a receiver or frame to which the buttstock is attached. Some parts of the operating mechanism of a firearm may also pass through the tang. A firearm may have an upper tang, a lower tang, or both.

Heel Cavity

A recess in the base of a bullet.

Box Magazine

A rectangular receptacle attached to or inserted into a firearm that holds cartridges stacked on top of one another ready for feeding into the chamber.

Recoil Plate

A removable collar or bushing in the breech face of certain firearms through which the firing pin passes. The bushing is often threaded and removable with a small pin spanner in order to change firing pins (e.g., Iver Johnson and Smith & Wesson top break revolvers). Also known as a firing pin bushing.

Firing Pin Bushing

A removable collar or bushing in the breech face of certain firearms through which the firing pin passes. The bushing is often threaded and removable with a small pin spanner in order to change firing pins (e.g., Iver Johnson and Smith & Wesson top break revolvers). Also known as a recoil plate.

Bushing

A removable lining used to reduce the effect of friction on moving parts or to decrease the diameter of a hole.

Sideplate

A removable plate in the frame or receiver of a firearm that allows access to internal parts or upon which some internal parts are mounted.

Magazine Fed

A repeating firearm in which the ammunition for subsequent firing is fed from a magazine.

Semiautomatic Action

A repeating firearm that requires a separate pull of the trigger for each shot fired, and which uses the energy of discharge to perform a portion of the operating or firing cycle. Also known as an autoloader or self-loader.

Butt, Round

A revolver grip with a rounded shape.

Rifle, Benchrest

A rifle designed for optimum accuracy while being shot from the shoulder and supported by a specifically designed table (rest).

Carbine

A rifle of short length and light weight originally designed for mounted troops.

Three-Quarters Stock

A rifle stock that has an abnormally long forend that does not reach the muzzle.

Whelan Stock

A rifle stock which features a forward sloping comb and cheekpiece.

Half Stock

A rifle stock with a forend which extends approximately to the midpoint of the barrel.

Trigger Guard

A rigid loop which partially surrounds the trigger to prevent damage or an accidental discharge.

Magazine Ring

A ring fixed to the lower part of the barrel which serves to support the magazine tube.

Lanyard Ring

A ring or loop on a firearm (typically a handgun) to which a lanyard may be attached.

Barrel Guide

A ring shaped attachment on the barrel of many shotguns and rifles which encircles the magazine tube.

Saddle Ring

A ring usually attached to the receiver of a firearm designed to be carried by a horseback rider.

Ejector Rod

A rod found on revolvers which is pushed rearward to facilitate extraction/ejection of cartridge cases or shotshells from a cylinder. This rod may be attached to the cylinder and provide simultaneous extraction/ejection of all cartridge cases, or housed in an ejector tube and individually extract/eject cartridge cases. Also known as rod ejector or extractor rod.

Recoil Spring Guide

A rod shaped device that fits inside of a recoil spring to guide and keep the spring from kinking.

Mainspring Guide

A rod-like device that keeps the mainspring from bending or twisting.

Wing Safety

A safety found on bolt action rifles which is usually mounted at the rear of the bolt assembly. The safety pivots up and down at right angles to the bore line in a manner of a bird's wing.

Pit

A scar on a metal surface usually the result of extensive rusting.

Takedown Screw

A screw found in many firearms to facilitate disassembly.

Stock Screw

A screw used for attaching the stock to the receiver or frame of a firearm. More than one may be used per firearm.

Strain Screw

A screw which bears against a leaf spring and will change the tension of the spring by its movement in or out.

Guard Screw

A screw(s) that extends from the trigger guard into or through the stock.

Barrel Weight

A separate weight attached to a regular barrel to change balance. A term for the size designation of barrel diameter (e.g., Winchester High Wall number 3 barrel).

Cartridge Case Rupture

A separation in the side wall of a cartridge case. Also known as cartridge case split.

Rib Marks

A series of raised and depressed features on the edges of radial and concentric fractures in bullet-struck glass and other comparable materials that, in the case of radial fractures start at right angles to the backside (exit) surface of the fracture and turn toward the source of breaking force. Rib marks on concentric fractures start at right angles to the front side (entry) surface.

Piston Ring

A sharp edged ring mounted on the piston of a gas operated firearm which makes a close seal between the piston and cylinder wall, and by scraping action reduces the accumulation of carbon in the cylinder.

Blown Pattern

A shot pattern, usually with a low percentage of pellets and of erratic distribution. Typically caused by pellets fired in a rifled barrel.

Choke, Swaged

A shotgun barrel interior constriction which has been formed at or near the muzzle by the use of dies or hammers.

Choke, Ventilated

A shotgun choke which is slotted for the release of powder gases.

Trap Gun

A shotgun specifically designed for the game of trap shooting.

Trap Shooting

A shotgun target sport in which clay targets are thrown away from the shooter by a reciprocating trap located forward of the firing line. May also be known as trapshooting.

Skeet Shooting

A shotgun target sport in which shooters move around a semi-circle and fire at clay targets thrown at specified angles from a high and a low "house", each containing a target trap.

Over-Bore

A shotgun whose barrel bore diameter is greater than the SAAMI maximum for that gauge.

Riot Gun

A shotgun with a short barrel designed for riot control or guard duty.

Skeet Gun

A shotgun with an open choke specifically designed for skeet shooting or close range hunting.

Shotgun, Double Barrel

A shotgun with two barrels adjacent to each other in the same plane. If arranged vertically, it is typically called an "over and under" shotgun. If arranged horizontally, it is typically called a "side-by-side" shotgun.

Scatter Load

A shotshell load designed to produce a wider spread and less dense pattern than a standard load at a close range in a choked gun. Also known as brush load, spreader load, and thicket load.

Field Load

A shotshell loaded for hunting small game animals and birds.

Try-Gun

A shoulder firearm with an adjustable stock that can be customized to the shooter's physical characteristics.

Telescope

A sight containing optical elements which magnify or enlarge the target.

Carrying Strap

A simplified version of a sling used for carrying purposes only.

Rifled Slug

A single projectile intended for use in smoothbore shotguns designed with spiral grooves for increased accuracy and a hollow base.

Slug, Rifled

A single projectile with spiral grooves and a hollow base that is intended for use in shotguns. The theory behind this design is that after leaving the muzzle of the gun, the slug will rotate and thus reach its target much more accurately.

Falling Block Action

A single shot lever actuated mechanism in which the breechblock slides vertically (or nearly vertically) when the lever is moved to expose or lock the breech. Also known as dropping block action (e.g., Ruger No. 1).

Fire Train

A single term that describes the sequence of events in the discharge of a cartridge: -The detonation of the primer. -The flame from the primer detonation passing into the -powder chamber via the flash hole(s). -The deflagration of the gunpowder and the subsequent production of gases. -The propelling of the projectile down the barrel by the above mentioned gases.

Non-Selective Single Trigger

A single trigger on double-barrel guns which fires the barrels in a fixed sequence.

Cartridge

A single unit of ammunition consisting of the cartridge case, primer, propellant, and with or without one or more projectile(s). Also applies to a shotshell.

Phantom Safety

A situation where the handler incorrectly senses or believes that a manually operated safety system has been engaged. This claim or theory usually arises with traditional single action revolvers and postulates that the trigger sear was perched rather than seated in the safety or quarter-cock notch of the hammer.

Hull

A slang term for a cartridge or shotshell case.

Blue Pill

A slang term given to a cartridge loaded to specified pressures higher than service loads to test firearm barrels during manufacture, but before assembly. Also known as a provisional proof cartridge

Barrel Jacket

A sleeve that surrounds the barrel. On certain firearms, the recoil spring is within the barrel jacket and is thus protected. Barrel jackets may be found on some machine guns to protect the shooter's hands from being burned by the hot barrel (e.g., Remington Model 8 and many sub-machine guns).

Feed Ramp

A sloped surface located at the mouth of the chamber that serves to guide the cartridge as it is fed from the magazine into the chamber. Also known as cartridge ramp or feed throat cartridge guide.

Pen Gun

A small caliber firearm shaped like a pen or pencil. These firearms may be converted smooth bore tear gas guns or have a rifled barrel.

Paper Disc

A small circular piece of treated paper cut and pressed into the primer cup in contact with the priming mixture. Also known as foil.

Orifice

A small hole or vent, such as the gas port in the barrel of a gas operated firearm or in the receiver or bolt body of a manually operated firearm.

Cocking Stud

A small lug in the cocking mechanism of the firearm.

Hammer Roll

A small roller installed at the bottom of the hammer which rides against the mainspring (e.g., Colt Single Action Army).

Skive

A small slit or cut in the ogive portion of a jacketed bullet for the purpose of improving expansion.

Grip Screw Bushing

A small tubular piece threaded inside and outside that is installed on the frame of certain pistols into which the grip screws are threaded (e.g., US 1911 pistol).

Percussion Cap

A small, generally cylindrical metallic cup containing a priming compound used to ignite the powder charge in muzzle loading firearms (placed on the nipple of percussion firearms).

Trap, Hand

A small, hand operated device for throwing clay targets.

Rib, Solid

A solid raised surface above a barrel or barrels which functions as a sighting plane.

Wound Ballistics

A special case in terminal ballistics dealing with the behavior of projectiles in tissue and tissue simulants. It includes bullet performance, penetration characteristics, and velocity loss as a consequence of the perforation of tissue and tissue simulants.

Target Sling

A special form of strap to aid target shooting.

Slave Action

A special substitute action used for testing a barrel or barrels.

Boattail Bullet

A specific design of projectile having a tapered or a truncated conical base.

Round Ball Bullet

A spherical projectile, usually made of lead or lead alloy.

Bullet Mold

A split block of metal having one or more cavities into which molten lead or lead alloy is poured and allowed to harden to form bullets. This process can produce toolmarks on the bullet(s) being molded.

Rifle, Varmint

A sporting rifle designed for long range small game hunting which features a heavy barrel and fires high velocity, flat trajectory bullets.

Varmint Rifle

A sporting rifle designed for long range small game hunting. Typically made with a heavier barrel and of a small caliber for high velocity projectiles with a flat trajectory.

Magazine Follower

A spring actuated device to push cartridges in a magazine to the feeding position.

Recoil Arm

A spring loaded arm which reaches up into the slide on certain semiautomatic pistols to absorb the recoil of the slide while moving rearward after firing (e.g., Webley and Scott pistol).

Detent

A spring loaded lock that engages a notch or indentation.

Sear Spring

A spring which puts pressure on the sear of a firearm to return the sear to its normal position upon release of the trigger.

Proof Mark

A stamp applied to a firearm after it has passed a proof test.

Laminated Stock

A stock which is made from two or more pieces of wood which have been glued together longitudinally.

Monte Carlo Stock

A stock with a raised comb to bring the eye in alignment with the sight.

Straight Stock

A stock with no pistol grip or one with less than the normal amount of drop.

Sling

A strap fastened to a firearm to assist in carrying or to steady it during firing.

Lanyard

A strap or cord attached to a firearm (usually a handgun) to prevent loss of the firearm.

Barrel Band

A strip or strips of metal that encircle and hold the barrel and stock, forend, magazine, or other accessories together.

Saboted Bullet

A sub-caliber projectile centered in a lightweight carrier to permit firing the sub-caliber projectile in a larger bore firearm.

Chamber, Floating

A system in which a moveable chamber operates the mechanism of a firearm. For example, the Colt 22 caliber conversion unit for the 1911 Government model pistol.

Long recoil Operation

A system in which the bolt and barrel recoil a greater distance than the length of the unfired cartridge. The breechblock is then held to the rear while the barrel is driven forward by its own spring. When the barrel is fully forward it trips the catch, releasing the breechblock, which then feeds the next cartridge into the chamber.

Blowback, Delayed

A system in which the breechblock is not locked but some mechanical delay is incorporated to ensure that the breechblock cannot move back with sufficient rapidity to allow the unsupported case to emerge from the chamber while the pressure is still high. Also known as retarded blowback.

Open Bolt System

A system of automatic or semiautomatic firing wherein the bolt remains in the rearward position after each shot or when firing is stopped. Generally weapons of this system have a fixed firing pin. Theoretically, the open bolt system allows for greater cooling to prevent cookoff and a simplified action (e.g., Thompson, Ingram/MAC M-10, and US M3 sub-machineguns). The Winchester Model 55, 22 caliber single shot rifle also fires from an open bolt. Also known as open-breech action.

Brinell Hardness Test

A system of hardness measurements commonly used for measuring metals and alloys and to determine the Brinell hardness number (abbreviated BHN) of that metal or alloy.

Janka-Hardness Test

A system of rating the hardness of wood by the use of a 0.444 inch diameter ball. The test involves measuring (in pounds) the amount of force required to push one half the diameter of the ball into the wood.

Benchrest

A table specifically designed to eliminate as much human error as possible by supporting a rifle for competitive shooting or for sighting-in purposes.

Free Rifle Stock

A target rifle stock used for position shooting matches. The word "free" refers to the fact that there are no restrictions on its configuration or weight.

Meplat

A term describing the flat, measurable portion of a bullet, specifically the tip's diameter.

Gusset

A term for the eight support brackets found in Remington plastic over-powder wads.

Ball Ammunition

A term generally used by the military for a cartridge with a full metal jacketed bullet or solid metal projectile.

Ball Cartridge

A term generally used by the military for a cartridge with a full metal jacketed bullet or solid metal projectile. Also known as Ball Ammunition.

Double Trigger

A term used for firearms having two barrels and a separate trigger for the discharge of each barrel. This term does not apply to firearms with double set triggers.

Copper Washed Bullet

A term used for lead projectiles with a thin copper colored coating. This finish is found extensively on 22 caliber bullets.

Season Cracking

A term used for stress-corrosion cracking that involves metallic cartridge cases or shotshell cups.

Cartridge Iris

A term used in industry to describe the circumferential discoloration around the neck or shoulder of brass cartridge cases as a result of the annealing process.

Magnum Cartridge

A term used to describe a rimfire or centerfire cartridge, or shotshell, that is larger, contains more shot, or produces higher velocities than standard cartridges or shotshells of a given caliber or gauge.

Burning Rate

A term used to describe the relative quickness of deflagration of a given powder as compared to a known standard. Burning rate is extremely important in determining a powder's suitability for a given cartridge.

Cartridge Designation

A term used to designate the specific cartridge for which a firearm is chambered.

Obliterated

A term usually referring to serial numbers which are no longer decipherable.

Bullet Puller

A tool used to remove a bullet from a cartridge. The most common bullet puller employs the inertia principle and is referred to as an inertia bullet puller.

Nipple Wrench

A tool used to remove or replace the percussion cap nipple on percussion firearms.

Decapper or Decapping Die

A tool used to remove primers from cartridge cases.

Inertia Bullet Puller

A tool used to remove the bullet from a cartridge by employing the inertia principle.

Carrier

A transfer mechanism in some firearms that raises and positions the cartridge or shotshell for feeding into the chamber. Also known as a lifter or elevator.

Forearm Tip Tenon

A transverse piece dovetailed into the underside of the barrels on certain rifles to accept screws from the sides to hold on the forearm tip (e.g., Marlin Model 39A).

Greener Cross Bolt

A transverse square or cylindrical locking bar which is contained in the standing breech of some hinged frame firearms and which locks into the barrel extension.

Thumb Trigger

A trigger mechanism actuated by pressing the thumb of the trigger hand on a button located directly behind the bolt.

Single Trigger

A trigger mechanism for multiple barrel firearms wherein repeated pulls of one trigger fires the barrels successively.

Single Set Trigger

A trigger system that permits setting the trigger by means of lever or bars, thus engaging it with the sear so that a very light trigger pull fires the gun. The trigger is typically set by pushing it forward until the engagement is felt and heard. Firing is accomplished by pulling the trigger rearward

Set Trigger

A trigger that can be engaged with the sear so that a very light pull will release the trigger. This is performed by means of levers or small bars. May be either a single set or double set trigger

Sheath Trigger

A trigger that has a minimal projection from the frame and is not usually surrounded by a trigger guard. Also known as a spur trigger.

Crisp Trigger

A trigger that releases the firing mechanism cleanly, suddenly, and unpredictably as pressure is applied. Also known as a clean break trigger

Spur Trigger

A trigger which has a minimal projection from the action and is not usually surrounded by a trigger guard. Also known as a sheath trigger.

Ejector Tube

A tube attached to the underside of the barrel of some single action revolvers which contains and guides the ejector rod. Also known as the ejector housing (e.g., Colt Single Action Army).

Primer Tube

A tube for holding primers in a handloading press.

Subcaliber Tube

A tube which is placed in the bore of a firearm to enable the firing of smaller or lower-powered ammunition.

Tubular Magazine

A tube-shaped magazine in which the cartridges are arranged end-to-end. It may be either under the barrel or in the buttstock.

Recoil Spring Plug

A tubular device, closed on one end that fits over a recoil spring at one end and rides against the barrel bushing. It is found on certain semiautomatic pistols and facilitates disassembly (e.g., US 1911 pistol).

Quill

A tubular projection upon which fits the cylinder of certain hinged frame revolvers (e.g., Iver Johnson Model 66 revolver). Also refer to Center Pin.

Swivel, Quick Detachable

A two part sling swivel which has a stud that is attached to the stock or barrel and a bow portion which is mounted on a spring plunger arrangement. The plunger passes through a hole in the stud for attachment of the bow to the firearm. They are sometimes called Q.D. Swivels, and allow for quick mounting and dismounting of a sling from a firearm.

Quick Detachable Swivel

A two part sling swivel which has a stud that is attached to the stock or barrel and a bow portion which is mounted on a spring plunger arrangement. The plunger passes through a hole in the stud for attachment of the bow to the firearm. They are sometimes called Q.D. swivels, and allow for quick mounting and dismounting of a sling from a firearm.

Double Pull Trigger

A two stage trigger pull wherein slack must be taken up before the resistance of the sear is encountered (e.g., Mauser Model 98.) Also known as a two-stage trigger.

Sleeved Barrel

A type of barrel construction which has an outer sleeve and an inner liner (e.g., Dan Wesson revolvers and Clerke 1st).

Undershot Wad

A type of card wad placed directly under the shot within the shotshell.

Star Crimp

A type of closure of the mouth of a metallic case or shotshell in which the sidewalls are folded in a star-shaped pattern. Also called rose crimp or a pie crimp.

Demi-Block

A type of double barrel construction in which the two barrels are fastened together at the breech by a vertical dovetail arrangement.

Cross-Bolt Safety

A type of firearm safety operated by lateral force on a button usually located in the trigger guard. Also known as a push button safety.

Lever Safety

A type of firearm safety operated by the movement of a pivoted lever (e.g., Luger pistol).

Rebounding Hammer

A type of firing mechanism wherein the hammer automatically retracts slightly to a rest position after causing ignition.

Lock, Rebounding

A type of firing mechanism wherein the hammer or striker retracts slightly to a rest position after causing ignition.

Inertia Firing Pin

A type of firing pin in which the forward movement is restrained until it receives the energy from a hammer blow. It is slightly recessed in the breech face before being struck by the hammer and is shorter in length than the housing in which it is contained. Upon hammer impact, the firing pin flies forward using only its own kinetic energy to strike and fire the primer [14] (e.g., Colt 1911 pistol).

Floating Firing Pin

A type of firing pin which is unrestrained by a spring or other mechanical means.

Rotary Magazine

A type of magazine in which the cartridges are arranged about a central rotating spindle or carrier. This type of magazine may be referred to as a Mannlicher magazine (e.g., Savage Model 99 and Mannlicher rifles).

Thumb Safety

A type of manual safety in which the external control component is located for convenient operation by the thumb of the trigger hand.

Battery Cup Primer

A type of primer using a flanged metallic cup as a holder for the primer components.

Revolver, Single Action

A type of revolver in which the hammer must be cocked manually to rotate the cylinder for each shot. The firearm is then discharged by a pull of the trigger. The process is repeated for each shot.

Revolver, Double Action

A type of revolver in which the rotation of the cylinder, cocking and firing are performed by a single pull of the trigger. Most double action revolvers can also be fired in the single action mode by manually cocking the hammer.

Tang Safety

A type of safety in which the external control component is mounted on the upper receiver tang of a firearm.

Vector Ammunition

A unique line of illuminating projectiles manufactured by the Hornady company that utilized an igniter composition followed by a fine zirconium wire centered in the lead core of these open-based pistol bullets. These special cartridges are no longer available.

Shotshell

A unit of ammunition that may contain a single projectile or multiple projectiles/pellets. Generally shotshells are designed to be fired from shotguns.

Feet Per Second

A unit of both speed and velocity of a projectile (abbreviated fps). The metric equivalent is meters per second (m/s).

Gunpowder

A variety of powders used in firearms as a propellant charge. A term commonly used when referring to cartridge and muzzle loading propellant.

Vented Test Barrel

A vented barrel used by ammunition manufacturers to provide ballistic data of revolver ammunition. The barrel takes into account cylinder gap, barrel length, powder position, production tolerances, and allows for reasonable wear and tear.

Lead-In Mark

A visible, thin, elongated deposition of bullet wipe transferred to a surface as a bullet first makes contact with that surface at a shallow incident angle. The lead-in mark is useful in establishing the direction of fire and travel of the projectile.

Wedge

A wedge shape device found on many percussion, and a few modern firearms. It holds the barrel assembly to the frame or stock (e.g., Colt 1851 Navy and Steyr Model 1912 pistol).

Shot Bridging

A wedging action of shot pellets in a tube causing a stoppage of flow in a shotshell loading or reloading operation.

Inconclusive:

A. Agreement of all discernible class characteristics and some agreement of individual characteristics, but insufficient for an identification. B. Agreement of all discernible class characteristics without agreement or disagreement of individual characteristics due to an absence, insufficiency, or lack of reproducibility. C. Agreement of all discernable class characteristics and disagreement of individual characteristics, but insufficient for an elimination.

Trigger Shoe

An accessory which is attached to the trigger to give a larger, non-slip bearing surface

Blow Forward

An action design found in some semiautomatic pistols in which the breech is stationary and the barrel moves forward when fired to open the action and eject the fired cartridge case (e.g., Schwarzlose, model 1908, 32 Auto Pistol).

Trap Door Action

An action in which a top hinged breechblock pivots up and forward to open. Locking on this action is accomplished by a cam located at the rear of the breechblock that fits into a mating recess (e.g., 1873 Springfield). Also known as a cam lock.

Single Action

An action requiring the manual cocking of the hammer or striker. Sufficient pressure on the trigger then releases the firing mechanism.

Slide Action

An action which features a movable forearm that is manually actuated in a motion parallel to the barrel by the shooter. Forearm motion is transmitted to a breech bolt assembly which performs all the functions of the firing cycle assigned to it by the design. Also known as pump action.

Auxiliary Cartridge

An adaptation to a firearm that enables the firing of smaller or lower power ammunition. Sometimes called an adapter, subcaliber device, or auxiliary chamber.

Subcaliber Device

An adaptation to a firearm to enable the firing of smaller or lower-powered ammunition. Also known as an adapter, auxiliary cartridge or auxiliary chamber.

Auxiliary Chamber

An adaptation to a firearm to enable the firing of smaller or lower-powered ammunition. Sometimes called an adapter, auxiliary cartridge, or subcaliber device.

Choke, Variable

An adjustable device attached to the muzzle of a shotgun that allows for control of shot patterns. Also known as adjustable choke.

Palm Rest

An adjustable support for a target rifle extending downward from the forearm.

Wood's Metal

An alloy consisting of 50% bismuth, 25% lead, 12.5% tin, and 12.5% cadmium. It melts at approximately 150 degrees Fahrenheit (65 degrees Celsius) and can be used for making castings of chambers, barrels, etc.

Cupronickel

An alloy of copper with nickel.

Infrared Spectroscopy

An analytical method whereby a chemical compound is identified by passing infrared radiation through a thin layer of the material and measuring the pattern of absorption bands which are characteristic for the compound. Applications of infrared spectroscopy include the identification of the plastic components of shotshells and the identification of gunpowder.

Minute of Angle (M.O.A.)

An angular measurement method used to describe accuracy capability. A minute of angle is one sixtieth of a degree. It subtends 1.047 inches at 100 yards, which for practical shooting purposes is considered to be one inch. A minute of angle group, therefore, equals one inch at 100 yards, two inches at 200 yards, etc. At 8" for example, it is approximately .002".

Cartridge Case Extractor Groove

An annular groove cut in rimless, semi-rimmed, or belted cartridge cases forward of the head for the purpose of providing a surface that the extractor may grip to remove the case from the chamber.

Extractor Groove

An annular groove cut in rimless, semi-rimmed, or belted cartridge cases forward of the head for the purpose of providing a surface that the extractor may grip to remove the case from the chamber.

Selective Single Trigger

An arrangement on double-barrel firearms having a single trigger which enables the shooter to choose the barrel to fire first. The mechanism will then subsequently switch to the unfired barrel, which can be fired with a second pull of the trigger.

Stop, Hand

An attachment beneath the forend or forearm of a target rifle to restrict the forward movement of the hand. Often used to attach a target sling.

Shell Holder

An attachment used in handloading to hold a cartridge case.

Sub-Machine Gun

An automatic or selective fire firearm chambered for a pistol cartridge. These firearms are normally compact, and intended to be used at close combat ranges.

Gas Operated

An automatic or semiautomatic firearm in which the propellant gases are used to unlock the breech bolt and to complete the cycle of extracting and ejecting. This action is usually performed in conjunction with a spring that returns the operating parts to battery (e.g., Remington Model 1100, US M1, US M14, US M16, and IMI Desert Eagle).

Recoil Operated

An automatic or semiautomatic type firearm in which the force of recoil is used to unlock the breech bolt and then to complete the cycle of extracting, ejecting, and reloading.

Grip Safety

An auxiliary locking device on the grip of some handguns which prevents firing until it is depressed, typically accomplished by grasping the grip correctly (e.g., US 1911 pistol).

Gas Cutting

An erosive effect in a firearm or on the base and/or bearing surface of a bullet caused by the high velocity and high temperature of propellant gases. Refer to Blow-by.

Pitch

An expression used to indicate the relationship of the bore to the plane of the buttplate (pad). It is found by extending a line across the butt and drawing at right angles to this line an additional line through the highest point on the receiver or frame and measuring the distance from an extension of this line to a point at the base of the front sight bead. The pitch is said to be down if the described line is above the front sight and up if below. The pitch is normally down. Applies to shotguns, as pitch is not typically given for a rifle.

Hammer Nose

An extension on the front of some hammers which acts as the firing pin.

Detonation

An extremely rapid exothermic decomposition reaction which proceeds at a rate greater than the speed of sound within the reacting material (unlike deflagration). The normal mode of initiation is shock (such as a blasting cap or high level mechanical shock), or from initial combustion which, due to peculiarities of confinement or other circumstances accelerates to such a degree that a shock wave is formed. Behind the shock wave, is a reaction zone where material is converted to gaseous products at high temperature and pressure. The flow of the reaction is in the same direction as the propagation.

Ejection Port Marks

An indentation or striated mark at one or more locations on a cartridge case (typically found on the sidewall) produced as the result of striking the ejection port during the ejection process. Such marks may be reproducible.

Kernel

An individual particle of any of the various forms of smokeless powder or the various granulations of black powder. Also known as a granule.

Timing

An industry term referring to the mechanical process of rotating the cylinder of a revolver.

Dummy Cartridge

An inert cartridge which cannot be fired.

Downloading

An intentional reduction in propellant resulting in a cartridge that may produce less than standard chamber pressure while producing less than standard velocity for that specific cartridge.

Notch Sight

An open rear sight having either a "V," "U," or square shaped cut on its upper edge.

Gas Port

An opening in the barrel or receiver of a firearm for several purposes: (1) to allow the vented gas to operate a mechanism, (2) to reduce recoil, (3) to provide an escape route for high-pressure gases should a case or primer rupture upon firing, reducing the amount of gas that might be directed back through the action into the shooter's face. May also be known as a gas vent.

Ejection Port

An opening in the receiver or slide to allow for ejection of a cartridge, cartridge case, or shotshell.

Microscope

An optical instrument consisting of a combination of lenses which allows the operator to view a magnified image of a small object(s).

Stereomicroscope

An optical instrument which provides three dimensional viewing of an object through paired objectives and eyepieces. Some models share a common, main objective.

Release Trigger

An unconventional mechanism in which the firearm is fired by the release of rather than the pull of the trigger. Pulling the trigger sets the sear, which cocks the hammer (or striker). Releasing the trigger allows the hammer (or striker) to discharge the firearm.

Barrel Blank

An unfinished barrel in any state of completion.

Wildcat Cartridge

Any cartridge not standardized within the shooting industry or not standardized domestically within the Sporting Arms and Ammunition Manufacturers Institute (SAAMI). These cartridges typically arise from an individual altering existing cartridge cases to suit their own needs and are not mass produced [21].

Centerfire Cartridge

Any cartridge that has its primer central to the axis in the head of the cartridge case.

Hangfire

Any delay in firing of an abnormal duration. This implies that firing does eventually occur. Also known as Delayed Fire.

Delayed Fire

Any delay in firing of an abnormal duration. This implies that firing does eventually occur. Also known as Hangfire.

Cocking Indicator

Any device that indicates that a firearm's hammer or striker is cocked.

Recoil Absorber

Any device that reduces the perceived recoil of a firearm.

Repeater

Any firearm equipped to hold more than one shot without reloading.

Top Break

Any firearm on which the barrel or barrels are allowed to tip down at the muzzle, exposing the chamber(s) for loading or unloading.

Muzzle Loader

Any firearm which is loaded with gunpowder and projectile(s) through the muzzle end of the bore or through the front end of a cylinder in the case of a muzzle loading revolver.

Misfeed

Any malfunction during the feeding cycle of a repeating firearm resulting in the failure of a cartridge or shotshell to enter the chamber completely. Also known as failure to feed.

Bullet Recovery System

Any method that will allow the recovery of a fired, undamaged bullet. Different systems are needed for various cartridges depending on bullet composition, jacket thickness, and velocity. Water tanks and cotton boxes are most commonly used.

Secondary Projectile

Any object which, due to the energy imparted by the primary projectile(s), becomes a missile. Examples include buttons, glass chips, splinters of wood, or bone.

Detachable Magazine

Any of a large array of magazines which are removable from the firearm for reloading.

Sight

Any of a variety of structures or devices, mechanical or optical, designed to assist in aiming a firearm.

Crown

Any of various forms of muzzle treatment meant primarily to protect the rifling. Includes chamfering of the bore, counterbore, or radius. Also known as muzzle crown.

Witness Panel

Any one of a variety of materials such as thin cardstock or poster board positioned and mounted in such a way so as to "witness" or record the position and orientation of a perforating projectile(s). Cardstock witness panels are also used to record pellet patterns from shotgun discharges at selected ranges. The patterns of gunshot residue deposits are also recorded on witness panels of selected materials for this purpose.

Target Rifle

Any rifle designed and equipped for match or target shooting.

Explosive

Any substance that violently changes to a gaseous form with accompanying heat and pressure through a chemical reaction.

Port Pressure

Applies only to gas operated firearms. The amount of pressure remaining in the bore as the bullet passes the gas port. If port pressures are too high, damage can result from the violent cycling of the action. It is important to understand that this can occur even when chamber pressures are within acceptable limits.

Service Cartridge

Commercially loaded, sporting ammunition intended to meet the full service requirements of the targeted consumer. Typically military and/or departmental issued ammunition. Also known as service load or duty ammo.

Toolmark, Impressed

Contour variations on the surface of an object caused by a combination of force and motion where the motion of the tool is approximately perpendicular to the plane being marked. The class characteristics (shape) can indicate the type of tool used to produce the mark. These marks may contain class, subclass, and/or individual characteristics of the tool producing the marks. Also known as compression marks.

Toolmark, Striated

Contour variations, generally microscopic, on the surface of an object caused by a combination of force and motion where the motion of the tool is approximately parallel to the plane being marked. Friction marks, abrasion marks, and scratch marks are terms commonly used when referring to striated marks. These marks may contain class, subclass, and/or individual characteristics of the tool producing the marks.

Cartridge Cook-off

Cook-off occurs when intense heat ignites the gunpowder inside a cartridge and causes it to discharge. This can occur during extreme overheating: (1) in a firearm chamber such as in machine guns, (2) due to fires, (3) without the operation of a firing mechanism.

Comparison Microscope

Essentially two microscopes connected to an optical bridge which allows the viewer to observe two objects simultaneously with the same degree of magnification. This instrument can have a monocular or binocular eyepiece. May also be referred to as a comparison macroscope.

Hyper-Obturation

Excessive swelling or upset of a bullet or cartridge case beyond the obturation required to make a seal for a normal firing event. Examples include expansion within an oversized barrel or chamber of a firearm (e.g., 9mm Luger cartridge fired in a 40 S&W chamber) or a high pressure event causing a bulged or flared bullet or cartridge case either inside or upon exit from the firearm's barrel or chamber (e.g., mushrooming of a hollow bullet base from a short barrel).

Screws, Stockmakers Hand

Extra-long screws used by stockmakers during the inletting operation to maintain alignment of the trigger guard and other auxiliary items with the action. Also known as inletting screws or guide screws.

Shooting Glasses

Eye protection and/or sight improvement specifically designed for use when shooting firearms.

Subclass Characteristics

Features that may be produced during manufacture that are consistent among items fabricated by the same tool in the same approximate state of wear. These features are not determined prior to manufacture and are more restrictive than class characteristics.

Small Bore Cartridge

General term applied in the United States to 22 caliber rimfire cartridges.

Benchrest Stock

Generally, a large and heavy stock used exclusively for benchrest shooting.

Shot

Generally, spherical pellets used in loading shotshells or cartridges. Shot can be found in many compositions such as lead, steel, bismuth, tungsten-polymer, tin, zinc, etc.

Lead Shot

Generally, spherically shaped pellets compared of lead used in loading shotshells or cartridges. Also refer to Hard Shot and Soft Shot.

Bolt Guides

Grooves or ridges on either the bolt or receiver intended to maintain alignment or prevent over rotation.

Powder

Gunpowder; a commonly used term for the propellant in a cartridge or shotshell.

Range of Conclusions Possible When Comparing Toolmarks

Identification, Inconclusive, Elimination, Unsuitable

Extractor Mark

Impressed or striated toolmarks produced on a cartridge, cartridge case, or shotshell as a result of contact with the extractor. These marks are usually found on the outer edge or just ahead of the rim, the underside of the rim, or in the extractor groove.

Propellant

In a firearm, the chemical composition that generates gas when ignited by the primer. The gas propels the projectile(s). Also known as gunpowder. Refer to the Gunshot Residue and Gunpowder Section for various types of gunpowder.

Comb

In a long gun, the ridge at the upper forward part of the buttstock just behind the wrist.

Pinch Point

In painted metal surfaces, a small area of surviving paint that was pinched between the initial contact point of a low incident angle bullet and the painted metal surface. The pinch point establishes the entry side of an impact or ricochet mark and thereby the bullet's direction of travel.

Frame

In revolvers, pistols, and break-open guns, the basic unit of a firearm which houses the firing and breech mechanism and to which the barrel and grips are attached. Refer to Receiver.

Plated Shot

Lead shot covered with a thin layer of a different metallic material to increase shot hardness and to reduce in-bore shot deformation. Typically copper and nickel are used to plate shot.

Dust Shot

Lead shot of small size (0.040in/1.016mm or smaller in diameter) normally used in making shot cartridges for small caliber ammunition.

Small Arms and Light Weapons

Man-portable weapons made or modified to military specifications for use as lethal instruments of war that expel a shot, bullet, or projectile by action of an explosive. Small arms are broadly categorized as those weapons intended for use by individual members of armed or security forces. They include handguns, rifles, carbines, sub-machine guns, and light machine guns. Light weapons are broadly categorized as those weapons designed for use by two or three members of armed or security forces serving as a crew, although some may be used by a single person. They include heavy machine guns, hand-held under-barrel and mounted grenade launchers, portable anti-aircraft guns, portable anti-tank guns, recoilless rifles, man-portable launchers of missile and rocket systems, and mortars.

Individual Characteristics

Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to that tool to the practical exclusion of all other tools.

Facets (on bullets)

Multiple flat, squarish impressions on the nose and ogive of a bullet that has perforated previously shattered tempered glass. These facets are produced during the bullet's impact with the small, diced pieces of broken glass.

Industrial Cartridge

Normally a blank cartridge used in various industrial applications, such as stud drivers, brake testing, and dog training devices. May be color coded to designate level of loading (light, medium, heavy, extra heavy, magnum).

Headstamp

Numerals, letters, and symbols (or a combination thereof) stamped into the head of a cartridge case or shotshell to identify the manufacturer, caliber, gauge, or other additional information.

Impression Evidence

Objects or materials that have retained the characteristics of other objects or materials through physical contact (e.g., firing pin impressions, breech face impressions, footwear impressions, tire impressions).

Recoil Shield

On a revolver, a lateral extension of the standing breech to each side, to prevent fired or unfired cartridges from coming out of the chambers and to protect the otherwise exposed primers of unfired cartridges.

Forearm/Forend Iron

On some guns, an intermediate part that holds the wood against the barrel and frame and retains the latch mechanism.

Frame Lug

On some revolvers, the projection from the side of the frame located at the rear of the cylinder window, that prevents the cylinder from detaching from the crane/yolk when the cylinder is in the open position (e.g., Smith and Wesson Model 36 revolvers).

Reamer

One of many spiral or straight-fluted, multi-edged cutting tools used to size and shape a hole.

Cylinder Stop Notch

One of the machined grooves on the circumference of a revolver cylinder that is engaged by the cylinder stop in order to ensure barrel and chamber alignment. Also known as bolt notch.

Bolt Notch

One of the machined grooves on the circumference of a revolver cylinder that is engaged by the cylinder stop in order to ensure barrel and chamber alignment. Also known as cylinder stop notch.

Case Cannelure

One or more circumferential rings around a cartridge case typically used by manufacturers to denote a certain type of load or product line.

Hammer Notch

One or more grooves on the hammer which engages a firing or safety component such as the sear.

Ammunition

One or more loaded cartridges consisting of a primed cartridge case, propellant, and with or without one or more projectiles. Also referred to as fixed ammunition or live ammunition (slang term).

Locking Lugs

One or more projections from the breech bolt which serve to lock it into place when closed and may or may not be an integral part of the breech bolt. Also known as a bolt lug.

Actuator

Part of the firing mechanism in certain automatic firearms which slides forward and back in preparing each cartridge to be fired. Component operated either manually or mechanically which transmits certain action or energy to other components which are dependent upon movement of the actuator in order to function. Also known as a trigger actuator.

Retractor

Part used to move a breech bolt to rear.

Case

Refers to cartridge case. The term may be shortened through common usage.

Copper Units of Pressure (C.U.P)

Relates to firearm discharge pressure measured by a copper crusher testing system. These values provide a means of testing and evaluating peak pressure generated during the discharge of a suitably modified firearm.

Sighting-Shot

Shot(s) fired to determine point of impact.

Paper Shell

Shotshells which are constructed with a body made from paper tubing.

Assault Weapon

Slang term to describe any firearm with a military appearance or large magazine capacity.

Slippage Marks

Slippage marks are typically produced by revolvers and have the appearance of widening of the land impressions at their beginning point. Also known as skid marks or jump marks.

Brass Washed Bullet

Sometimes referred to as golden bullets. This coating has been used on 22 caliber bullets.

Microscopic Marks

Striae, patterns of minute lines or grooves, or impressions in an object which are generally smaller than the unaided eye can distinguish. In firearm and toolmark identification, these marks are characteristic of the object which produced them and are the basis for identification.

Firing Pin Aperture Shear

Striated marks caused by the rough edges of the firing pin aperture scraping the primer metal during unlocking of the breech. Refer to Primer Flow-Back.

Axial Engraving

Striations or contours on a fired bullet that run parallel or approximately parallel to the axis of the bullet. There are several possible types of axial engravings, including, but not limited to marks left by or due to: 1) the mouth of the cartridge case; 2) the chamber throat; 3) irregularities or burrs along the forward edge of a chamber in a revolver cylinder; 4) inconsistent rotation of a bullet as it moves down the bore; 5) misalignment of a revolver chamber with the axis of the bore (also known as forcing cone marks, misalignment marks, or out-of-time marks); and 6) the rifling, prior to engagement with and rotation of the bullet (also known as slippage marks, skid marks, or jump marks).

Recoil Tables

Tables that list recoil velocity and recoil energy of specific cartridges fired in specific firearms.

Firing Pin

That part of a firearm mechanism which strikes the primer or rim of a cartridge to initiate ignition in order to fire a cartridge or shotshell. Refer to Hammer Nose and Striker.

Barrel

That part of a firearm through which a projectile or shot charge travels under the impetus of powder gasses, compressed air, or other like means. A barrel may be rifled or smooth.

Swivel Bow

That part of a swivel which is in the form of an elongated loop and to which a sling or carrying strap is passed through or otherwise attached.

Receiver Bridge

That part of the receiver on bolt action rifles that arches over the rear of the bolt hole.

Chamber Throat

That section of the bore of a rifled gun barrel located immediately ahead of the chamber in which the rifling is conically removed to provide clearance for the seated bullet. Also known as ball seat or leade.

BB Cap

The abbreviation of bulleted breech cap. The original design in 1845 was a percussion cap without a well-defined head loaded with a 22 caliber ball. A rimfire cartridge designed for use in Flobert rifles for indoor use.

Gyroscopic Stability

The ability of a fired bullet to remain stable in flight due to its spin.

Shocking Power

The ability of a projectile to dissipate its kinetic energy effectively into a target.

Resolving Power

The ability of an optical system to render two closely spaced points as distinct. The resolving power of a lens is usually measured by its ability to distinguish parallel lines of equal width equidistantly spaced by an amount equal to the width of each line and is stated in terms of lines per millimeter of the image.

Metal Fouling

The accumulation of lead or bullet jacket material in the bore of a firearm from the passage of projectiles. Also known as leading.

Pressure Determination

The act of measuring the pressure generated during the firing process in cartridges or shotshells contained in the chamber of a test barrel.

Pattern Matching

The act of visually comparing the surface contours of two or more striated or impressed toolmarks for corresponding and/or differentiating features.

Sporterize

The act or process of converting a military firearm to a sporting firearm, usually by removing unneeded accessories and altering the barrel and/or stock.

Regulating Barrels

The adjusting of the relationship of the axes of multi-barreled firearms so as to make the points of impact coincide.

Zero

The adjustment of a firearm's sights in order to obtain impact at a desired point in relation to a specific point of aim at a given range.

Bullseye

The aiming point in target shooting; usually the center of the target.

Muzzle Wave

The air that is compressed and moves out spherically from the muzzle of a firearm after firing a projectile.

Orienting

The aligning of two bullets, which were fired from the same barrel, on the comparison microscope so that the land and groove impressions on those bullets which were produced by the same lands. and grooves in the barrel are opposite each other. The term can also refer to the alignment of cartridge cases or other toolmark-bearing surfaces, so that directionality of marks made by the same tool are consistent on both stage of the comparison microscope. Sometimes called phasing or indexing.

Cartridge Case Capacity

The amount by weight, in grains of water, of a particular type of powder that can be inserted in a cartridge case with the bullet fully seated, without compressing the powder charge.

Lock Energy

The amount of energy delivered to the primer from the firing pin blow.

Trigger Pull

The amount of force which must be applied to the trigger of a firearm to cause sear release. It is measured by hanging weights or an instrument touching the trigger at a point where the trigger finger would normally rest. The force applied during measurement is approximately parallel to the bore axis.

Powder Charge

The amount of gunpowder by weight in a cartridge or shotshell.

Rifling Pitch

The angle at which the rifling is cut in relationship to the axis of the bore. It is usually stated as the number of inches required for one revolution, for example one turn in 12 inches. Also known as rate of twist.

Yaw

The angle between the longitudinal axis of a projectile and the line of the projectile's trajectory. Yaw is usually considered to exist before a bullet achieves full gyroscopic stability.

Criminalistics

The application of scientific techniques in collecting and analyzing physical evidence in criminal cases.

Setting

The arming of a set-trigger mechanism of a firearm so equipped.

Breechblock

The block in breech-loading firearms that locks the rear of the barrel against the force of the charge and prevents gases from escaping; also provides support for the head of the cartridge case during firing.

Magazine Floorplate

The bottom of a magazine.

Ballistics, Interior

The branch of ballistics dealing with all aspects of the combustion phenomena occurring within a firearm, including pressure development and motion of the projectile along the bore of the firearm. Also known as internal ballistics.

Ballistics, Terminal

The branch of ballistics which deals with the effects of a projectile's impact at the target.

Ballistics, Exterior

The branch of ballistics which studies the motion of a projectile from the muzzle of a firearm to the time it impacts the target.

Barrel Shank

The breech end of the barrel that fits into the action or receiver.

Selective Fire

The capability of some automatic firearms to fire in either the automatic or semi-automatic mode at the firer's discretion. These firearms normally have a switch or selector lever to facilitate the operator's choice.

Energy, Bullet

The capacity of a projectile to do work in flight. The units are typically expressed as foot-pounds, joules, or kilogram-meters. Also known as projectile energy.

Cylinder Flare

The circular gray-to-black deposit around the front margin of the chamber(s) of a revolver composed of gunshot residues deposited during the firing process. Also known as a smoke ring, halo, or simply flare.

Neck Tension

The circumferential stress that the case neck exerts on the seated bullet, as a result of the fit provided by inside diameter of the case neck and the outside diameter of the bullet.

Seating Lines

The circumferential striae which are parallel to the axis of the projectile, generated on the surface of the bullet by the cartridge case. Also known as bullet seating marks or cartridge case mouth marks.

Overshot Wad

The closure disc over the top of the shot column held in place by a rolled crimp. Also known as a top wad.

Rolled Crimp

The closure of the mouth of a shotshell by inverting the mouth of the tube over a top wad or slug, or a crimp to hold a bullet in a cartridge.

Locked

The condition in a firearm action in which the bolt or breechblock is solidly secured in a fixed relationship with the chamber so as to resist being blown back by chamber pressure.

Primer Setback

The condition when a primer, or battery cup primer assembly, moves partially out of its proper location in the primer pocket of a cartridge or shotshell during firing.

Cartridge Case

The container for all the other components which comprise a cartridge. Serves as a gas seal during the firing of a cartridge.

Ricochet

The continued flight of a rebounded projectile and/or major projectile fragments after a low angle impact with a surface or object.

Ogive

The curved portion of the bullet forward of the bearing surface.

Shoulder Radius

The curved surface between the body and the shoulder of a cartridge case.

Neck Radius

The curved surface between the neck and the shoulder of a cartridge case.

Rechamber

The cutting of a new chamber in a barrel to accommodate a cartridge of the same bore diameter.

Bullet Shearing

The cutting of metal from a bullet due to a cylinder misalignment in a revolver. Also known as shaving.

Tube

The cylindrical body of a shotshell.

Drop Fire

The discharge of a loaded firearm as a result of an impact after being dropped. This may be the consequence of a design shortcoming, a compromised safety system, or the failure of the handler to engage the appropriate safety device. Also refer to Jar Off.

Snap-Fire

The discharge of a loaded firearm through the inadvertent release of the hammer or striker from a partially retracted position. Such discharge may be the consequence of a compromised safety system, the lack of a safety system for such an event, or the failure on the part of the handler to engage the appropriate safety system.

Bolt Stroke

The distance a bolt travels from the "fully open" to the "fully closed" position.

Overtravel

The distance a part travels after a particular event occurs in the normal operation of the firearm (e.g., the rearward motion of the trigger after the sear or hammer release or the rearward motion of a bolt beyond ejection, etc.).

Spread, Extreme

The distance between the centers of the two shots which are the farthest apart in a group of shots on a target.

Cartridge Case Head Clearance

The distance between the head of a fully seated cartridge and the face of the breech bolt when the action is locked. Commonly confused with headspace.

Barrel Length

The distance between the muzzle end of the barrel and the face of the closed breechblock or bolt. On revolvers, it is the overall length of the barrel including the threaded portion within the frame. Barrel length normally should include compensators, flash hiders, etc., if permanently affixed.

Length of Pull

The distance from the center of the trigger to the center of the buttplate or recoil pad. Applies to both rifles and shotguns.

Headspace

The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.

Bullet Jump

The distance that a bullet must travel from its position at rest in the cartridge case to its initial engagement with the rifling of the barrel. Also known as free travel.

Firing Pin Protrusion

The distance the firing pin protrudes from the breech face when in its forward most position.

Bullet Penetration

The distance which a bullet travels in a target material.

Pattern

The distribution of shot fired from a shotgun. Among firearms manufacturers, pattern is generally measured as a percentage of pellets striking a 30-inch circle at 40 yards. Some 410 bore or skeet guns are measured with a 30-inch circle at 25 yards. In Firearm Identification, the term is used to describe the distribution of either shotshell pellets or gunpowder particulate.

Shock Wave

The disturbance of air surrounding and behind the bullet caused by a compression of the air column directly in front of the bullet.

Underlocking Lug

The downward projecting lug(s) at the breech end of a hinged frame firearm used for locking and barrel positioning in the frame.

Driving Edge

The driving edge of a bullet fired from a gun with a right twist is the right edge of the land impression, or the left edge of the groove impression. The driving edge of a bullet fired from a gun with left twist is the left edge of the land impression or the right edge of the groove impression. Also known as leading edge when used in conjunction with the term following edge.

Altitude Effect

The effect on velocity, and therefore projectile trajectory and shot pattern, caused by changes in atmospheric density due to altitude.

Barrel Time

The elapsed time from the contact of a firing pin with a cartridge primer to the emergence of the projectile(s) from the muzzle of the firearm.

Ignition Barrel Time

The elapsed time from the contact of a firing pin with a cartridge primer to the emergence of the projectile(s) from the muzzle of the firearm.

Muzzle

The end of a firearm barrel from which the projectile emerges.

Rifling Head

The end of a hook or cut rifling tool which holds the cutter and deepens the groove with subsequent passes.

Tumbling

The end-over-end rotation of an unstable projectile in flight. May also be referred to as bullet tipping, keyholing, or yaw.

Energy, Muzzle

The energy of a fired projectile(s) measured at the muzzle of a firearm.

Energy, Terminal

The energy of a projectile(s) measured at the point of impact.

Bullet Jacket

The envelope enclosing the core of a projectile that is typically of metallic construction.

Primer Leak

The escape of gas between the primer cup and head of the cartridge case or shotshell.

Blow-by

The escaping of gases past the bullet, while the bullet is in the barrel. May also be used in reference to leakage of gas around a bullet fired through the baffles in a suppressor. Refer to Blow-by in the Suppressor Terminology section. Blow-by is often used erroneously as a slang term for blowback.

Function Testing

The examination of a firearm concerning its mechanical condition and operation. It is usually performed to determine if all safety features are operable and/or if the firearm is capable of firing a cartridge. Refer to Accidental Discharge Test, Jar Off, Drop Fire, and Safety Testing.

Safety Testing

The examination of a firearm to determine if it is capable of accidental fire (i.e., if it will fire without the trigger being pulled) and if the safety features of the firearm are operational. Also known as an Accidental Discharge Test. Refer to Function Testing, Jar Off, and Drop Fire.

Malfunction

The failure of a firearm to function properly. Malfunctions can be caused by the firearm, ammunition, and/or human factors.

Rim

The flanged portion of the head of a rimfire cartridge, certain types of centerfire rifle and revolver cartridges, and shotshells. The flanged portion is usually larger in diameter than the cartridge or shotshell body diameter and provides a projecting lip for the extractor to engage. In a rimfire cartridge, the rim provides a cavity into which the priming mixture is placed.

Backthrust

The force exerted on the breechblock by the head of the cartridge case during propellant burning.

Recoil Energy

The force of the firearm's movement opposite to the direction of the bullet, usually expressed in foot-pounds (ft-lbs) or joules (J).

Air Resistance

The force placed on an object by the atmosphere in opposition to forward motion. Also known as aerodynamic drag.

Bullet Pull

The force required to pull a bullet from the case mouth. Also referred to as neck tension.

Bullet Push

The force required to shorten a cartridge by pushing on the bullet.

Bolt Head

The forward end of the bolt embodying the bolt face/breech face.

Forend

The forward part of a one-piece stock

Forend, Beavertail

The forward part of a stock, typically found on a shotgun, that is greater in width than standard forends. The beavertail provides a better grip for the forward hand, and protects the hand from hot barrels during fast shooting.

Forearm

The forward part of a two-piece stock.

Radial Fractures

The fractures or cracks that radiate out from an impact site in non-crystalline materials such as glass, ceramics, bone and certain plastics.

Cylinder End-Play

The free longitudinal movement of the cylinder in the frame of a firearm. Also known as end shake.

Extractor Hook

The hook on the forward end of the extractor which engages the extractor groove for removing a cartridge, cartridge case, or shotshell from the chamber of a firearm.

Primer

The ignition component of a cartridge.

Musket Cap

The ignition source for most military muzzle loading rifles of the Civil War era, usually consisting of a copper alloy cup containing the priming mix. They are larger than percussion caps and typically incorporate continuous or segmented flanges (wings) at the cup mouth for ease of handling.

Crimp

The inward shaping of the mouth of a cartridge case or shotshell to secure the projectile(s). Crimps are categorized as follows: roll, star or rose, fold, stab, semi-circular, or split ring and possibly others. Crimps may also be used to retain primers in primer pockets.

Cup, High

The length of the external metal cup on a shotshell; refers to a cup of high metal head construction. May be incorrectly referred to as high base.

Cup, Low

The length of the external metal cup on a shotshell; refers to a cup of low metal head construction. May be incorrectly referred to as low base.

Shot Column

The length of the shot load in a shotshell.

Ocular

The lens or combination of lenses nearest the eye of the viewer in an optical instrument that is designed to further magnify the primary image of the objective. Also known as an eyepiece.

Eyepiece

The lens or combination of lenses nearest the eye of the viewer in an optical instrument that is designed to further magnify the primary image of the objective. Also known as an ocular.

Hand

The lever attached to the trigger that rotates a revolver cylinder. This action positions the next breech chamber in front of the barrel. Also known as the cylinder pawl.

Cylinder Pawl

The lever attached to the trigger that rotates a revolver cylinder. This action positions the next breech chamber in front of the barrel. Also known as the hand.

Top Lever

The lever located on top of the breech end of hinged frame firearms. When pushed to one side, the lever will unlock the barrel(s) from the frame and allow it to be moved. Also known as top snap.

Bolt Body

The main part of the bolt that is typically tubular in shape, has locking lugs on it, and contains the firing pin, firing pin spring, extractor(s), and sometimes the ejector.

Groove Diameter

The major diameter of a barrel which is the diameter of a circle circumscribing the bottom of the grooves in a rifled barrel.

Microfractology

The microscopic study and comparison of fracture surfaces. Light or scanning electron microscopes are often used.

General Rifling Characteristics

The number, width, and direction of twist of the lands and grooves in a barrel of a given caliber firearm.

Cast-On

The offset of the butt of a firearm to the left for a left-handed shooter with a dominant left eye to keep a straight line of focus on the target without having to tilt the head.

Cast-Off

The offset of the butt of a firearm to the right for a right-handed shooter with a dominant right eye to keep a straight line of focus on the target without having to tilt the head.

Mouth

The open end of a cartridge case or shotshell, from which the projectile(s) is expelled in firing.

Hand Slot

The opening in a revolver frame through which the hand protrudes to index the cylinder.

Cartridge Case Mouth

The opening in the cartridge case into which the projectile(s) is seated.

Resizing, Full Length

The operation of completely reforming a fired cartridge case to approximately its original dimensions.

Resizing, Neck

The operation performed by reloaders to reduce only the neck diameter of a fired cartridge case.

Neck Sizing

The operation performed by reloaders to reduce or restore the original neck diameter of a fired cartridge.

Barrel Diameter

The outside dimension of a barrel at any given point.

Crane

The part of a solid frame revolver on which the cylinder is swung out to the side to accomplish loading and ejecting. Also known as yoke.

Standing Breech

The part of the frame of a revolver or break-open firearm which supports the head of the cartridge when it is fired.

Front Strap, Grip

The part of the frame that forms the front of the grip of pistols and revolvers.

Infrared

The part of the invisible spectrum of light that is contiguous to the red end of the visible light spectrum. The infrared spectrum of light comprises electromagnetic radiation of wavelengths from approximately 800 nm to 1mm.

Loading Density

The percentage of the measured volume of propellant compared with the available cartridge case volume.

Trigger Creep

The perceptible movement of the trigger after takeup or pretravel prior to sear release.

Point of Impact

The point at which a projectile hits a target.

Wrist

The portion of a rifle or shotgun stock located behind the action which is normally grasped by the shooter's trigger hand.

Chamber Pressure

The pressure in a firearm generated by the expanding propellant gases after ignition. Normally measured by means of piezoelectric transducers or crusher gauges. Also known as breech pressure or barrel pressure.

Residual Pressure

The pressure level that remains in the cartridge case or shotshell within the firearm's chamber and in the bore immediately after the projectile leaves the muzzle of the firearm.

Bullet Sizing

The process of forming a cast bullet to the proper size by forcing it through a lubricator/sizing tool. This process can produce toolmarks on the bullet.

Barrel Swaging

The process of forming the interior and/or exterior shape of the barrel of a firearm by pneumatic or hydraulic hammering around a mandrel. Also known as hammer forging.

Chamber Casting

The process of making a cast of the chamber of a firearm to determine the cartridge for which the firearm is designed, or to better observe imperfections within that chamber.

Reloading

The process of manually reassembling a fired cartridge case with a new primer, propellant, and bullet or wads and shot. Also known as handloading.

Extraction

The process of removing a cartridge, cartridge case, or shotshell from the chamber of a firearm.

Firelapping

The process of shooting bullets coated with a fine abrasive substance in order to remove toolmarks from the barrel and increase the accuracy of the firearm.

Rib Extension

The protrusion of a rib beyond the muzzle end of a barrel.

Twist Rate

The rate at which the rifling of the firearm turns within the bore. This is normally expressed as the distance required for the rifling (and projectile) to make one complete revolution. Depending on the origin of the firearm, this may be written in inches or in millimeters (e.g., 1 turn in 12 inches or 1 turn in 305mm).

Magnifying Power

The ratio of apparent size of an object viewed through an optical instrument to its actual size, e.g., 4X. This means the object would appear 4 times larger than it actually is.

Sectional Density

The ratio of the weight of a bullet in pounds to the square root of its diameter in inches.

Butt Stock

The rear end of a long gun which is normally placed against the shooter's shoulder.

Chamber

The rear part of the barrel bore that has been formed to accept a specific cartridge or shotshell. In a revolver, the holes in the cylinder represent multiple chambers.

Recoil

The rearward movement of a firearm resulting from firing.

Prescribed Load

The recommended combination of cartridge components as defined by SAAMI or the manufacturer for any cartridge or shotshell.

Cartridge Case Neck

The reduced diameter, cylindrical portion of a cartridge case that extends from the top of the shoulder to the cartridge case mouth.

Cartridge Case Sizing

The reduction in diameter of a cartridge case by forcing it into a die of smaller diameter than the case.

Sizing

The reduction in diameter of a cartridge case or bullet by forcing it into a die of smaller diameter than the cartridge case or bullet, respectively.

Cylinder Alignment

The relationship of the axis of the chamber in a revolver cylinder to the axis of the bore.

Barrel Arrangement

The relationship to each other, in which multiple barrel systems are positioned in forearms (e.g., over and under, side-by-side, etc.).

Dry Firing

The releasing of the firing pin on an unloaded chamber of a firearm.

Mold Line

The residual line on an object, such as a cast bullet, resulting from the flow of metal into the juncture where the two mold halves come together.

Light Hit

The result of insufficient firing pin energy or protrusion which causes erratic ignition or failure to detonate the priming compound. Also known as a light blow.

Cylinder

The rotating component of a firearm that contains the chambers.

Bullet Spin

The rotational motion imparted to a bullet by the rifling in the barrel.

Barrel Threads

The screw threads found on the muzzle end or shank of the barrel that are used to screw attachments onto the muzzle end of the barrel or to screw the barrel into the frame or receiver of the firearm, respectively.

Obturation

The sealing of a bore and chamber by pressure. During the firing process, pressure swells the cartridge case against the chamber walls which minimizes the rearward flow of gases between the case and the chamber wall. The same pressure, applied to the base of the projectile, causes it to swell or upset, filling and sealing the bore.

Cartridge Case Shoulder

The section of a bottleneck cartridge case connecting the main body of the cartridge case and the smaller diameter neck.

Shoot-Off

The separation of the mouth end of a shotshell from the body when it is fired.

Sympathetic Firing

The simultaneous firing of two or more cartridges chambered in the cylinder of a revolver, one of which is in battery.

Girth

The smallest circumferential dimension at the pistol grip. Applies to both rifles and shotguns.

Ball Burnishing

The smoothing of the tops of the lands of a rifled barrel by the forced passage of a hardened steel ball of appropriate diameter. Also known as ballizing.

Monoblock

The solid section at the breech end of some multibarrel guns into which the barrels are inserted.

Bullet Splash

The spatter and fragmentation of a bullet upon impacting a hard surface.

Impact

The striking of one thing against another; collision (e.g., a bullet or projectile strike on a target).

Forensic Science

The study and application of science to the purpose of the law.

Elevation

The term used to designate the vertical movement of an adjustable sight to cause the fired bullet to strike the point of aim at various ranges.

Lock-Time

The time interval between sear release and the firing pin striking the primer.

Ignition Time

The time interval between the impact of the striker or firing pin on the primer, and a rise in pressure sufficient to start the bullet from its seated position in the cartridge case. The elapsed time from the moment of firing pin contact on the primer to the point on the x (time) axis equal to the point where the pressure-time curve indicates propellant burning has initiated.

Canting

The tipping or tilting of a gun to one side at the time it is fired.

Sprue Cutter Mark

The toolmark left on the base of a cast bullet which results from cutting off the sprue.

Firing Pin Drag Mark

The toolmark produced when a projecting firing pin comes into contact with a cartridge case or shotshell during the extraction/ejection cycle.

Time of Flight

The total elapsed time that a projectile requires to travel a specific distance from the muzzle.

Trailing Edge

The trailing edge of a bullet fired from a gun with a right twist is the left edge of the land impression, or the right edge of the groove impression. The trailing edge of a bullet fired from a gun with left twist is the right edge of the land impression or the left edge of the groove impression. Also known as following edge when used in conjunction with the term leading edge.

Jump

The upward and rearward recoiling movement of a firearm when it is fired.

Necking Down

The use of case forming dies to reduce both outside and inside diameter of a cartridge case neck.

Velocity, Remaining

The velocity of a projectile at any point of its trajectory.

Velocity, Summit

The velocity of a projectile at the highest point of the trajectory.

Velocity, Instrumental

The velocity of a projectile(s) that is recorded by suitable instrumentation located at a predetermined distance from the muzzle of a test barrel or a firearm.

Drop

The vertical distance from the line of sight to the comb, Monte Carlo, or heel of the stock. For rifles, it is measured as a straight line drawn from the top of the front sight through the top surface of the open rear sight adjacent to the notch. The drops for target rifles are usually measured from the centerline of the bore. For shotguns, it is measured as a straight line drawn from the base of the front bead sight across the highest point on the frame or receiver.

Air Space

The volume in a loaded cartridge not occupied by the propellant, bullet, wads, or shot. Also known as ullage.

Column Wad

The wads between propellant and projectiles in a shotshell.

N-Wave

The wave generated at the base or heel of a bullet when that bullet's velocity exceeds the speed of sound.

Bore Erosion

The wear on the bore of a firearm caused by the action of the propellant powder and/or the friction of the projectile(s).

Barrel Erosion

The wearing or physical deterioration of the bore of a firearm caused by hot powder gases or projectile passage.

Test Fire

To discharge a firearm in a laboratory or controlled setting in order to obtain representative bullets and cartridge cases for comparison or analysis, to determine functionality of the firearm, or to produce gunshot residue or shot patterns at known distances.

Fire

To shoot or discharge a firearm.

Ejector Marks

Toolmarks produced by the ejector on the head of a cartridge case or shotshell.

Reloading Dies

Tools which hold and/or reform cartridge cases or shotshells during a reloading operation.

Balled Shot

Two or more shot pellets joined together during the process of manufacturing or during firing. Usually caused by hot propellant gases leaking past the wadding and fusing the shot while the shot is still in the barrel. Also known as fused shot.

Ammunition Lot

Typically refers to a single production run of ammunition and is designed with a code made up of numerical and/or alphabetical digits. Both a military and commercial ammunition term.

Bench Block

Usually hardened steel or nylon with holes and channels cut into it that facilitate the disassembly of a firearm when used in conjunction with drifts and hammers.

Shot Protector Wad

Various designs of shot cups made of plastic and designed to reduce pellet deformation during barrel travel. Also known as a shot cup.

Reload

(1) A cartridge which has been reassembled with a new primer, powder, projectile(s), and/or other components. (2) To create a cartridge by loading new components into a previously fired cartridge case.

Reference Ammunition

(1) A collection and cataloging of both cartridges and ammunition components utilized by the firearm examiner; may include both unfired and fired ammunition components. Also known as ammunition standards, known standards, or fired standards. (2) Ammunition used in test ranges to evaluate test barrels, ranges, and other velocity and pressure measuring equipment. May also be used as a control sample by which other characteristics are compared, such as accuracy, patterns, etc.

Hammer Strut

(1) A component part of the firing mechanism of some firearms which is connected between the hammer and trigger. This piece acts to move the hammer to the firing position when the trigger is pulled. (2) A pivoting rod-like piece of metal attached to the hammer of certain firearms, which guides a coil mainspring to power a hammer (e.g., Colt US 1911 pistol).

Gas Tube

(1) A cylindrical piece on gas operated firearms through which propellant gases are channeled to directly impinge on the bolt. (2) A cylindrical piece on gas operated firearms which houses the gas piston.

Inertia Block

(1) A device intended to function during recoil to set the fire control mechanism to fire a second barrel. (2) A device intended to function during recoil to prevent doubling on some double barrel shotguns.

Trigger Stop

(1) A device to prevent overtravel of the trigger. (2) A device to prevent certain firearms from being fired until the finger lever is closed.

Hammer Block

(1) A device which separates the firing pin from the hammer except when the trigger is pulled. (2) A safety device which restricts hammer movement.

Flash Hole

(1) A hole(s) pierced or drilled through the web in the primer pocket of a metallic cartridge case. May also be known as a Gas Vent or Gas Port. (2) The hole in the end of a battery cup primer used in shotshells. May also be known as a Gas Vent or Gas Port. (3) The hole in a percussion nipple. May also be known as a Gas Vent or Gas Port.

Sabot

(1) A lightweight carrier in which a subcaliber projectile(s) is centered to permit firing in a larger bore firearm. (2) An enclosure to facilitate the firing of shot usually in a rifled barrel.

Cut-Off

(1) A manually operated mechanical device which prevents cartridges from being fed from the magazine into the loading mechanism. This device can be used to convert an automatic, semiautomatic, or bolt action firearm to fire single shot. (2) A mechanical device that is employed in firearms so that only one cartridge or shotgun shell will feed into the carrier, or lifter, with each cycle of the breech mechanism. Also known as shell stop or cartridge stop.

Charger

(1) A metal device which may hold five to ten cartridges used to rapidly load the magazine of a pistol or rifle. In some rifles, clip guides are machined into the receiver to guide the charger into the proper position for magazine loading. The empty charger may either be removed manually or ejected as the bolt closes. Also known as a stripper clip. (2) A term sometimes improperly used to describe removable magazines.

Escutcheon

(1) A metal or plastic reinforcement around a hole. (2) A metal part which displays a name or trademark.

Trigger Plate

(1) A metal plate fitted to the lower part of some frames through which the trigger(s) pass. (2) A component attached to the frame or receiver of some firearms which supports the major components of the firing mechanism and may have the trigger guard as an integral part.

Magazine Plug

(1) A part inserted in a magazine to reduce its capacity. (2) A part in the end of a tubular magazine which closes the end and retains the spring.

T-Bolt

(1) A patented reciprocation and locking system for use on a rimfire rifle. (2) Sometimes used to describe straight pull bolt action rifles with a horizontally protruding straight bolt handle.

Patch

(1) A piece of paper or cloth wrapped around a ball or lead bullet to prevent leading of the barrel and to improve the gas seal. (2) A piece of cloth used with a rod to clean the bore of a firearm.

Tip-up Pistol

(1) A pistol that is hinged near the rear sight that allows the barrel to tip up at the muzzle, exposing the chamber(s) for loading or unloading (e.g., Smith & Wesson Model 1). (2) A pistol that is hinged near the muzzle that allows the barrel to tip up at the breech, exposing the chamber for loading or unloading (e.g., Beretta model 21 Bobcat).

Armor Piercing Bullet

(1) A projectile consisting of a hardened core or wholly composed of a substance other than lead or lead alloy. (2) Any projectile manufactured, represented, or designed to be metal or armor piercing.

Tenon

(1) A projecting wood component of a firearm that fits into the receiver or frame. (2) The portion of the rimfire bullet which fits into the brass case; from bullet base to bottom of band. Also known as the heel.

Rebound Slide

(1) A reciprocating device found in some double action revolvers which moves the hammer into a position in which there is no contact of either hammer and firing pin or firing pin and primer. It can also be used to position a safety device between the hammer and firing pin or primer in such revolvers. (2) A spring loaded metal block which directly impinges on the trigger in Smith & Wesson revolvers. The rebound slide causes the trigger to return to its forward position and rebounds the hammer. It is the primary safety.

Magazine

(1) A secure storage place for gunpowder, ammunition, or explosives. (2) A container for cartridges which has a spring and follower to feed those cartridges into the chamber of a firearm. The magazine may be detachable or an integral part of the firearm.

Knurling

(1) A series of ridges or diamonds impressed or cut into a surface to help prevent slipping. (2) May be used to refer to cannelures on cartridge cases or bullets.

Flyer

(1) A shot considerably outside the normal group on a target. (2) A shot considerably outside the normal range with regards to velocity or pressure.

Shotshell, One Piece

(1) A shotshell component having the body and base wad as a single unit with a metallic cup. Sometimes called a unibody shell. (2) A complete round of ammunition having the body and base wad as a single unit without a head of a different material.

Slug

(1) A single projectile for shotshells. (2) A slang term for a fired bullet.

Hair Trigger

(1) A slang term for a trigger requiring very low force to actuate. (2) The light pull of a second trigger in a double set trigger mechanism.

Mid-Range

(1) A term that defines a specific point in the trajectory of a projectile that is half the distance between the firearm and the target. (2) A reduced velocity, centerfire cartridge used principally in target shooting.

Gauge

(1) A term used in the identification of a shotgun bore. The gauge is equal to the number of round lead balls of bore diameter that equal one pound. Thus 12 gauge is the diameter of a round lead ball weighing 1/12 pound. (2) An instrument or device for measuring or testing a parameter such as a headspace gauge or trigger pull gauge.

Caliber

(1) A term used to designate the specific cartridge for which a firearm is chambered. (2) In firearms, caliber is the approximate diameter of the circle formed by the tops of the lands of a rifled barrel, typically expressed in hundredths of an inch (38 caliber) or millimeters (9mm caliber). (3) In ammunition, caliber is a numerical term, without the decimal point, included in a cartridge name to indicate the nominal bullet diameter.

Crossbolt

(1) A transverse operating type of lock used on some double barrel or break open firearms. (2) A form of manual safety which operates transversely to prevent or permit firing of a firearm.

Single Stage Trigger

(1) A trigger mechanism in which the trigger travel is relatively short and there is no significant, perceptible change in pull force from the beginning of movement up to the point of firing. (2) A trigger which releases with a single pull.

Target Trigger

(1) A trigger which provides a large bearing surface for the trigger finger. (2) A trigger mechanism which provides for adjustment of such characteristics as pull force, travel, or overtravel. (3) A relatively light, crisp trigger designed to assist in accurate shooting.

Grain

(1) A unit of weight (avoirdupois). The grain unit is commonly used in American and English ammunition practice to measure the weight of components. There are 7,000 grains in a pound and 437.5 grains in one ounce. (2) An individual kernel of black powder.

Shoe

(1) An adapter fastened to a trigger to widen the surface. (2) An insert in the forearm of a side-by-side double barreled shotgun by which the forearm is attached to the barrels. Also known as forend iron or forend plate.

Brass

(1) An alloy principally composed of copper and zinc in varying proportions, often used in the manufacture of cartridge cases, primer cups, and bullet jackets. (2) A slang term sometimes used to refer to fired cartridge cases.

Range

(1) An area equipped for testing firearms and ammunition. (2) The horizontal distance between the firearm and the target.

Sleeve

(1) An insert of special material placed in a barrel to reduce bore erosion, renew an eroded bore, alter bore diameter, or to strengthen the barrel. (2) A tube surrounding the receiver of a target rifle to improve rigidity. Refer to Barrel Liner and Barrel - Sleeved Barrel.

Port

(1) An opening in a receiver to allow loading or ejection. (2) An opening in the wall of a barrel or bolt body to allow gas to escape, operate a mechanism, or reduce sensible recoil.

Magnum

(1) Any cartridge or shotshell, that is larger, contains more shot, or produces higher velocities than standard cartridges or shotshells of a given caliber or gauge. (2) Firearms that are designed to fire magnum cartridges or shotshells.

Proof Cartridge

(1) Definitive - A cartridge loaded to specified pressures higher than service loads. Used only for testing assembled firearms or elements of firearms which contain the primary firing pressure. (2) Provisional - A cartridge loaded to specified pressures higher than service loads to test firearm barrels during manufacture, but before assembly. Sometimes called a blue pill.

Overall Length

(1) For a firearm, it is the dimension measured parallel to the axis of the bore from the muzzle to a line at a right angle to the axis and tangent to the rearmost point of the butt plate or grip. (2) For ammunition, it is the greatest dimension of a loaded cartridge. For centerfire and rimfire cartridges, it is the measurement from the face of the head to the tip of the bullet. For shotshells or blanks, it is the measurement from the face of the head to the crimp. Overall length does not refer to the uncrimped length of a shotshell.

Fluting

(1) Grooves cut in the chamber wall of a firearm to assist or retard cartridge case extraction (e.g., Russian Tokarev semiautomatic rifle and the Heckler and Koch model HK4 pistol). (2) Longitudinal grooves cut into the outside surface for all or some portion of the overall barrel length. (3) A defect in a brass cartridge case usually in the form of a shallow indentation caused by excessive oil present in dies during manufacture, in resizing dies during handloading operations, or in a chamber during firing. Also known as oil dent.

Clip Guides

(1) Grooves cut in the receiver of certain firearms with fixed magazines to direct the stripper clip used to load the firearm into position (e.g., Mauser 98 rifle). (2) Devices that can be attached to the top of removable magazines to allow stripper clips to be used to load the magazine (e.g., M-16/AR-15 type rifle).

Phasing

(1) In Firearm and Toolmark Identification, the marking of specimens (bullets, cartridge cases, or toolmarks) which were fired by the same firearm or created by the same tool, orienting the features which show the alignment of corresponding detail (match). Also known as orienting or indexing. (2) A method for marking cartridges and bullets to orient the position of test cartridges in a firearm. Also known as orienting or indexing.

Selector

(1) In a double barreled firearm, a device to allow the shooter to choose which barrel is to be fired by the first pull of the trigger. (2) A lever which enables the shooter to choose the type of fire -automatic, burst, or semiautomatic, high or low rate of automatic fire.

Buffer

(1) In a firearm, any part intended to absorb shock and check recoil. (2) In a shotshell, the plastic granular particles that some manufacturers use to prevent the deformation of the shot pellets in the shotshell and to protect the bore when the shot travels down the barrel.

Pitch

(1) In barrel rifling, the distance a bullet must travel in the bore to make one revolution. (2) In grips, the angle that the front of the handgun grip makes with the line of sight. (3) In shotguns, pitch is an expression used to indicate the relationship of the bore to the plane of the buttplate (pad). It is found by extending a line across the butt and drawing at right angles to this line an additional line through the highest point on the receiver or frame and measuring the distance from an extension of this line to a point at the base of the front sight bead. The pitch is said to be down if the described line is above the front sight and up if below. The pitch is normally down. (4) A component used in making clay targets.

Anvil

(1) In cartridge case with a boxer primer assembly, the anvil is an internal metal component against which the priming mixture is crushed by the firing pin blow. (2) In a Berdan primed cartridge case, a metal component in the primer pocket against which the priming mixture is crushed by the firing pin blow. (3) In rimfire firearms, the breech end of the chamber.

Indexing

(1) In firearms, the rotation and stopping of a revolver cylinder and the quality of alignment between the axis of the chamber and the axis of the bore. (2) In Firearms Identification, the marking of specimens (bullets or cartridge cases) which were fired by the same firearm, orienting the features which show the alignment of corresponding detail (match). Also known as orienting or phasing. (3) A method for marking cartridges and bullets to orient the position of test cartridges in a firearm. Also known as orienting or phasing.

Gas Cylinder

(1) In gas operated firearms, the housing for the gas piston. (2) A compressed gas container for use as ammunition in air guns.

Butt

(1) In handguns, it is the bottom part of the grip. (2) In long guns, it is the rear or shoulder end of the stock.

Grip

(1) In handguns, the handle. (2) In long guns, the portion of the stock located behind the action which is normally grasped by the shooter's trigger hand. Also known as the wrist.

Bullet Upset

(1) In interior ballistics, it is the change of a bullet's form due to chamber pressure. (2) In exterior ballistics, it is the expansion of a bullet upon impact with target.

Solid Frame

(1) In long guns, one in which the barrel and receiver are not designed for quick disassembly. (2)In handguns, a frame that is not hinged.

Patched Ball

(1) In modern cased ammunition, the term refers to a full metal jacketed bullet (FMJ). (2) A round or conical lead projectile that utilizes cloth, paper, or other material which acts as a gas seal or a guide for the projectile. An early type of fixed ammunition.

Velocity, Terminal

(1) In popular use, refers to the striking velocity. (2) In small arms ballistics, it is the constant speed of a projectile after air drag and gravitation pull have reached the point where the two forces cancel each other's effect on the projectile

Stippling

(1) In reference to firearms, it is the roughing of wood or metal with a pointed tool. It is normally performed to provide a gripping or decorative surface. Also known as matting. (2) In reference to gunshot residue, refer to Powder Stippling in the Gunshot Wound Terminology Section of the appendix.

Bore Diameter

(1) In rifled barrels, it is the distance across the center of the barrel from the top of one land to the top of the opposite land. (2) In shotguns or muskets, it is the distance across the center of the barrel forward of the chamber but before any restrictive choke or expanded muzzle.

Soft Shot

(1) Lead shot manufactured by the process of pouring molten lead through colander and allowing the droplets to free-fall into water in a shot tower. (2) Lead shot containing less than 0.5% alloying metal. Also known as drop shot.

Reticle

(1) Markings in a microscope eyepiece used to establish location or scale. Commonly used to measure rifling. (2) The aiming reference seen when looking through a telescopic sight. It may consist of straight or tapered lines, dots, or other marks used to determine the point-of-aim, size of, or range to the target.

Gas Vent

(1) Refer to Gas Port in reference to firearms. (2) Any hole(s) pierced or drilled through the web in the primer pocket of a metallic cartridge case or the end of a battery cup primer of a shotshell. May also be known as a Gas Port or Flash Hole. (3) The hole in a percussion nipple. May also be known as a Gas Port or Flash Hole.

Long Rifle

(1) Term originally used to refer to long barreled flintlock rifles. (2) The name given to one type of a 22 caliber rimfire cartridge

Stripping

(1) The act of disassembling a firearm. (2) The act of transferring cartridges from a loaded stripper clip to a magazine, or a magazine to a chamber. (3) The failure of a bullet to engage the rifling when traversing down the barrel.

Chambering

(1) The act of inserting a cartridge into the chamber. (2) The reaming of a chamber in a barrel blank or cylinder.

Shoulder

(1) The act of placing a shotgun or a rifle to a shooter's shoulder to align the sights and fire at a target. (2) The sloping portion of a metallic cartridge case that connects the neck and the body of a bottleneck cartridge. (3) The square, or angular step between two diameters on a barrel, pin, stud, or other part commonly used in firearms.

Fusing

(1) The balling of lead shot due to gas leakage. (2) The melting of the core of a jacketed bullet. (3) The melting of a lead alloy bullet.

Shot String

(1) The characteristic elongation of a column of shot in flight. (2) The distance between the leading and trailing pellets of a shot charge in flight.

Load

(1) The combination and quantity of components used to assemble a cartridge or shotshell. (2) The act of putting ammunition into a firearm magazine or chamber. The following are various types of loads encountered in ammunition

Pellet

(1) The common name for the spherical projectiles loaded into shotshells. Also known as shot. (2) A nonspherical projectile used in some air rifles and air pistols.

Cocking Piece

(1) The end of a long firing pin or striker by which the firearm may be cocked manually. (2) An internal portion of the cocking mechanism which holds the firing pin or striker in its cocked position against the sear.

Beavertail

(1) The forend or forearm of a shotgun or rifle that is made wider than a standard forend or forearm [21]. (2) The wider than normal version of the M1911A1 grip safety.

Knuckle

(1) The front section of the water table upon which the barrels hinge. (2) The front section of the action bar flats.

Loading Gate

(1) The hinged piece attached to the frame of revolvers that can be opened to permit loading of the chambers. (2) A spring loaded cover for the loading port of a long gun.

Body (Case)

(1) The metallic portion of the cartridge case that contains the propellant, primer and projectile(s) (2) The tubular section of a shotshell that contains the propellant, wads, and projectile(s).

Sprue

(1) The opening through which metal or plastic can be poured into a mold. (2)The waste piece that is cast in the opening.