Firearms and Toolmarks Glossary
Assault Rifle
1. A compact, SELECT-FIRE, detachable box magazine-fed weapon, that utilizes a centerfire rifle cartridge and is designed primarily for military use. 2. A slang term, used INCORRECTLY to describe any firearm with a military appearance or large magazine capacity.
Magazine
1. 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 forearm. A. BLIND BOX - An integral magazine having a permanently closed bottom. Loading and unloading are accomplished through the same opening. B. BOX - 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. C. DETACHABLE - Any of a large array of magazines which are removable from the firearm for reloading. D. DRUM - 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 submachine guns. Examples: Thompson submachine gun, Luger, Russian PPSH and Degtyarov machine guns. E. ROTARY - A form of magazine in which the cartridges are arranged about a central rotating spindle or carrier. Examples: Savage Model 99 and Mannlicher rifles. F. STAGGERED COLUMN - A box magazine which, rather than having a single column of cartridges, has two columns staggered. This increases the capacity without lengthening the magazine. Examples: Browning Hi-Power and S&W Model 59. G. TUBULAR - A tube-shaped magazine in which the cartridges are arranged end-to-end. It may be either under the barrel or in the butt stock. 2. A secure storage place for gunpowder, ammunition, or explosives.
Flash Hole
1. A hole(s) pierced or drilled through the web in the primer pocket of a metallic cartridge case. 2. The hole in the end of a battery cup primer used in shotshells. 3. The hole in a percussion nipple.
Grain
1. A unit of weight (avoirdupois). 7000 grains equal one pound. 2. The grain unit is commonly used in American and English ammunition practice to measure the weight of components.
Anvil
1. An internal metal component in a boxer primer assembly against which the priming mixture is crushed by the firing pin blow. See PRIMER. 2. A metal feature in the primer pocket of a Berdan-primed cartridge case, against which the priming compound is crushed by the firing pin blow. 3. The breech end of the chamber in a rimfire firearm.
Rifling, Methods
1. BROACH, GANG - A tool having a series of cutting edges of slightly increasing height used to cut the spiral grooves in a barrel. All grooves are cut with a single pass of the broach. 2. BROACH, SINGLE - A non-adjustable rifling cutter which cuts all of the grooves simultaneously, and is used in a series of increasing dimensions until the desired groove depth is achieved. 3. BUTTON - A hardened metal plug with a rifled cross section configuration. It is pushed or pulled through a drilled and reamed barrel so as to cold form the spiral grooves to the desired depth and twist. When the carbide button was first introduced it was described as a SWAGING PROCESS or SWAGED RIFLING. 4. HOOK - A cutting tool which has a hook shape and only cuts one groove at a time. 5. SCRAPE - A cutting tool which cuts two opposing grooves at a time. 6. SWAGE - An internal mandrel with rifling configuration which forms rifling in the barrel by means of external hammering. Also known as HAMMER FORGING.
Caliber
1. Firearms: The approximate diameter of the circle formed by the tops of the lands of a rifled barrel. 2. Ammunition: A numerical term, without the decimal point, included in a cartridge name to indicate the nominal bullet diameter.
Cartridge Designation
1. Firearms: The approximate diameter of the circle formed by the tops of the lands of a rifled barrel. 2. Ammunition: A numerical term, without the decimal point, included in a cartridge name to indicate the nominal bullet diameter.
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 - full automatic or semiautomatic, high or low rate of automatic fire.
Blowback
1. In firearms, an automatic or semiautomatic firearm design that directly utilizes the breech pressure exerted on the head of the cartridge case to actuate the mechanism. 2. In ammunition, a leakage of gas rearward between the case and the chamber wall from the mouth of the case. See also BLOWBACK, DELAYED.
Grip
1. In handguns, the handle. 2. In long guns, that portion of the stock to the rear of the trigger. Also called WRIST.
Body-Case
1. Metallic portion of the case. 2. Shotshell - The tubular section that contains the propellant, wads and shot charge.
Chambering
1. The reaming out of a chamber in the end of a barrel blank or cylinder. 2. The act of inserting a cartridge in the chamber.
Indexing
1. The rotation and stopping of a revolver cylinder. 2. A method for marking cartridges and bullets to orient the position of test cartridges in the firearm. See ORIENT.
Shot Size
?
Bullet, Lead
A bullet formed from a lead alloy.
Bullet, Copper Jacketed
A bullet having an outer jacket of copper or copper alloy and containing a lead alloy core.
Bullet, Mushroom
A bullet that has expanded upon impact to a mushroom-like shape, or designed to so expand.
Bullet, Hollow Point
A bullet with a cavity in the nose to facilitate expansion.
Bullet, Semi-Jacketed
A bullet with a partial jacket exposing a lead nose with a cavity.
Cartridge Case, Rimmed
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.
Shotshell
A cartridge containing projectile(s) designed to be fired in a shotgun. The cartridge body may be metal, plastic or paper.
Primier, Centerfire
A cartridge initiator 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 as opposed to rimfire which must be struck on the circumference.
Load, Squib
A cartridge or shell which produces projectile velocity and sound substantially lower than normal. May result in projectile and/or wads remaining in the bore.
Reload
A cartridge which has been reassembled with a new primer, powder, projectile(s) and/or other components.
Cartridge Case, Semi-Rimmed
A centerfire cartridge case having a case head only slightly larger in diameter than the body and an extractor just forward of the head.
Cartridge Case, Rimless
A centerfire cartridge case whose case head is of the same diameter as the body, having a groove forward of the head to provide an extraction surface.
Cartridge Case, Rebated
A centerfire cartridge case whose rim diameter is smaller than the diameter of the body of the case.
Cannelure
A circumferential groove generally of a knurled or plain appearance in a bullet or cartridge case. Three uses include crimping, lubrication and identification.
Hammer
A component part of the firing mechanism which gives impulse to the firing pin or primer.
Trigger Bar
A connecting piece between the trigger and the sear.
Bullet, Wadcutter
A cylindrical bullet design having a sharp shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring.
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.
Mushroom
A descriptive term for a soft point, hollow point, or special type of bullet point that is designed to expand to increased sectional diameter with minimum weight loss upon impact with a target.
Action, Lever
A design wherein the breech mechanism is cycled by an external lever generally below the receiver.
Safety
A device on a firearm generally designed to return to the "on" (safe) position when the firearm is opened.
Hammer Block
A device which separates the firing pin from the hammer except when the trigger is pulled. A safety device which restricts hammer movement.
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.
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-Piping
A failure to eject in which the cartridge case is caught in the ejection port by the forward motion of the bolt or slide.
Handgun
A firearm designed to be held and fired with one hand.
Hammerless
A firearm having no hammer or having a concealed hammer.
Rifle
A firearm having rifling in the bore and designed to be fired from the shoulder.
Bolt Action
A firearm in which the breech closure: (1) is in line with the bore at all times (2) manually reciprocates to load, unload and cock, (3) is locked in place by breech bolt lugs and engaging abutments usually in the receiver. There are two principal types of bolt actions: the turn bolt and the straight pull.
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.
Revolver
A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis and be discharged successively by the same firing mechanism. See SINGLE ACTION and DOUBLE ACTION.
Double Action
A handgun mechanism in which a single pull of the trigger cocks and release the hammer.
Safety, Automatic
A locking device on some firearms designed to return to the "on" (safe) position when the firearm is opened.
Extractor
A mechanism for withdrawing the cartridge or cartridge case from the chamber.
Bullet
A non-spherical projectile for use in a rifled barrel.
Serial Number
A number applied to a firearm in order to identify the individual firearm.
Ejector
A portion of a firearm's mechanism which ejects or expels cartridges or cartridge cases from a firearm.
Bullet, Full Metal Jacket
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 and BALL AMMUNITION.
Bullet, Semi-Wadcutter
A projectile with a distinct, short truncated cone at the forward end.
Autoloading
A repeating firearm requiring 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 (usually the loading portion).
Stiker
A rod-like firing pin or a separate component which impinges on the firing pin.
Magazine Safety
A safety device found on some semiautomatic handguns that prevents firing unless the magazine is fully inserted into the firearm.
Cartridge
A single unit of ammunition consisting of the case, primer, and propellant with one or more projectile(s). Also applies to a shotshell.
Cap, Percussion
A small, generally cylindrical metallic cup containing a primary explosive used to ignite the powder charge in muzzle loading firearms.
Shotgun
A smooth bore shoulder firearm designed to fire shotshells containing numerous pellets or sometimes a single projectile.
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.
Blowback, Retarded
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.
Meplat
A term describing the blunt of a bullet, specifically the tip's diameter.
Bullet, Copper Washed
A term used for lead bullets with a copper colored coating. This finish is found extensively on 22 rimfire cartridges from manufacturers around the world.
Gauge
A term used in the identification of a shotgun bore. 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.
Obliterated
A term usually referring to serial numbers which are no longer readable.
Floating Firing Pin
A type of firing pin which is unrestrained by a spring or other mechanical means. See CHAMBER, FLUTED.
Bullet Jacket
A usually metallic cover over the bullet core.
Safety, Manually Operated
A. CROSS BOLT - A type of firearm safety operated by lateral force on a button usually located in the trigger guard. B. GRIP - An auxiliary locking device in the grip of some handguns which prevents firing until it is depressed. Example: US 1911 pistol. C. HALF COCK - This so-called safety is a sear engagement which holds the hammer back away from the firing pin. D. LEVER - A type of firearm safety operated by the movement of a pivoted lever. Example: Luger pistol. E. SLIDING BUTTON - A safety mechanism on a firearm that is operated by a sliding motion. F. TANG - A safety mounted on the upper receiver tang of a firearm. G. THUMB - A safety on a firearm so located as to be operated conveniently by the thumb of the trigger hand. H. WING - A safety found on bolt action rifles, usually mounted at the rear of the bolt assembly, and pivots up and down at right angles to the bore line in a manner of a bird's wing.
Single Action
An action requiring the manual cocking of the hammer before sufficient pressure on the trigger releases the firing mechanism.
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.
Gas Operated
An automatic or semiautomatic firearm in which the propellant gases are used to unlock the breech bolt and then to complete the cycle of extracting and ejecting. It is usually in conjunction with a spring which returns the operating parts to battery. Examples: Remington Model 1100. US M1, US M14 and US M16.
Grip Safety
An auxiliary locking device on the grip of some handguns which prevents firing until it is depressed. Example: US 1911 pistol.
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. One or more flash holes are drilled or pierced through the bottom of the primer pocket into the propellant cavity of the case.
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.
Projectile
An object propelled by the force of rapidly burning gases or other means.
Cartridge, Center Fire
Any cartridge that has its primer central to the axis in the head of the case.
Delayed Fire
Any delay in firing, of an abnormal duration. This implies that firing does eventually occur. Also known as HANG FIRE.
Bolt
Breech Bolt: The locking and cartridge head support mechanism of a firearm that operates in line with the axis of the bore. Cylinder Stop: A device to stop cylinder rotation in proper alignment with the barrel of a revolver. 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.
Subclass Characteristics
Discernible surface features of an object which are more restrictive than CLASS CHARACTERISTICS in that they are: 1. Produced incidental to manufacture. 2. Are significant in that they relate to a smaller group source (a subset of the class to which they belong). 3. Can arise from a source which changes over time. Examples would include: bunter marks, extrusion marks on pipe, etc. Caution should be exercised in distinguishing subclass characteristics from INDIVIDUAL CHARACTERISTICS.
Smooth Bore
Firearm with unrifled bore.
Groove
Helical grooves in the bore of a firearm barrel to impart rotary motion to a projectile.
Rifling
Helical grooves in the bore of a firearm barrel to impart rotary motion to a projectile.
Propellant
In a firearm, the chemical composition, which when ignited by a primer, generates gas. The gas propels the projectile(s). Also called POWDER; GUNPOWDER; POWDER, SMOKELESS.
Rifling, Polygonal
Lands and grooves having a rounded profile instead of the traditional rectangular profile.
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 and distinguish it from all other tools.
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 with a specific firearm.
Breech Face Markings
Negative impression of the breech face of the firearm found on the head of the cartridge case and/or primer after firing. Also see MATRIX.
Headstamp
Numerals, letters and symbols (or combination thereof) stamped into the head of a cartridge case or shotshell to identify the manufacturer, caliber, gauge or give additional information.
Ammunition
One or more loaded cartridges consisting of a primed case, propellant, and with one or more projectiles. Also referred to as FIXED or LIVE AMMUNITION.
Sear
Sear A part which retains the hammer or striker in the cocked position until the trigger is pulled.
Shot
Spherical pellets used in loading shotshells or cartridges.
Identifiable Striae
Striations in the evidence mark which can be identified with reproduced striations in the test marks. See STRIATIONS.
Throat
That area forward of the cartridge chamber, extending to the point of full bore diameter. Also known as LEADE or THROAT. See also FORCING CONE.
Magazine Well
That opening in a firearm action which receives a detachable magazine.
Trigger
That part of a firearm mechanism which is moved manually to cause the firearm to discharge.
Firing Pin
That part of a firearm mechanism which strikes the primer of a cartridge to initiate ignition. Sometimes called HAMMER NOSE or 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. May be rifled or smooth.
Breech Face
That part of the breechblock or breech bolt which is against the head of the cartridge case or shotshell during firing.
Bearing Surface
That portion of a bullet's outer surface that comes into direct contact with the interior surface of the barrel.
Gyroscopic Stability
The ability of a fired bullet to remain stable in flight due to its spin.
Ejection
The act of expelling a cartridge case from a firearm.
Extraction
The act of withdrawing a cartridge or cartridge case from the chamber of a firearm.
Firing Pin Hole
The aperture in the breech face through which the firing pin protrudes. Also see MATRIX.
Cartridge Case Head
The base of the cartridge case which contains the primer.
Receiver
The basic unit of a firearm which houses the firing and breech mechanism and to which the barrel and stock are assembled.
Cartridge Case
The container for all the other components which comprise a cartridge.
Bullet Ogive
The curved forward part of a bullet.
Cartridge Case Length
The dimension from face of the head to the mouth.
Bullet Wipe
The discolored area on the immediate periphery of a bullet hole, caused by bullent lubricant, lead, smoke, bore debris or possible jacket material. Sometimes called BURNISHING or LEADED EDGE.
Driving Edge
The driving edge of a fired gun with a right twist is the left edge of the groove impression, or the right edge of the land impression. The driving edge of a fired bullet with left twist is the right edge of the groove impression or the left edge of the land impression. Also called the LEADING EDGE.
Trailing Edge
The edge of a land or groove impression in a fired bullet which is opposite to the driving edge of that same land or groove impression. Also called the FOLLOWING EDGE when used in conjunction with the term "leading edge." See DRIVING EDGE.
Muzzle
The end of a firearm barrel from which the bullet or shot emerges.
Forend
The forward part of a one-piece stock.
Forearm
The forward part of a two-piece stock.
Derringer
The generic term applied to many variations of pocketsize pistols, either percussion or cartridge, made by manufacturers other than Henry Derringer, up to present time.
Nipple
The hollow, cone shaped piece at the breech of a percussion firearm onto which is placed the percussion cap. When fired, the flame from the percussion cap passes through a hole in the nipple and into the chamber to ignite the powder.
Primer
The ignition component of a cartridge.
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.
Bullet Core
The inner portion of a jacketed bullet, usually lead.
Bore
The interior of a barrel forward of the chamber.
Hand
The lever that rotates a revolver cylinder. Also known as CYLINDER PAWL.
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.
Bullet Diameter
The maximum dimension across the largest cylindrical section of a bullet.
Land and Groove Impression
The negative impressions on the bearing surface of a bullet caused by the rifling in the barrel from which is was fired.
General Rifling Characteristics
The number, width and direction of twist of the rifling grooves in a barrel of a given caliber firearm.
Cartridge Case Mouth
The opening in the cartridge case into which the projectile(s) is inserted.
Breech
The part of a firearm at the rear of the bore into which the cartridge or propellant is inserted.
Half-Cock
The position of the hammer of a firearm when about half retracted and held by the sear so that it cannot be released by a normal pull of the trigger.
Full Cock
The position of the hammer or striker when the firearm is ready to fire.
Seating
The positioning of a primer or bullet in a cartridge case.
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.
Land
The raised portion between the grooves in a rifled bore.
Chamber
The rear part of the barrel bore that has been formed to accept a specific cartridge. Revolver cylinders are multi-chambered.
Recoil
The rearward movement of a firearm resulting from firing.
Cartridge Case Neck
The reduced diameter, cylindrical portion of a cartridge case, extending from the top of the shoulder to the case mouth.
Cylinder
The rotatable part of a revolver that contains the chambers.
Forensic Science
The study and practice of the application of science to the purpose of the law (Forensic Science Foundation).
Test Firing
The term used to designate the actual firing of a firearm in a laboratory to obtain representative bullets and cartridge cases for comparison or analysis.
Theory of Identification
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." 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 it 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 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. Currently the interpretation of individualization/identification is subjective in nature, founded on scientific principles and based on the examiner's training and experience.
Firing Pin Drag Mark
The toolmarks produced when a projecting firing pin comes into contact with a cartridge case or shotshell during the extraction, ejection cycle. Also see MATRIX.
Pump Action
The working mechanism of a firearm. May be broken down into action types as follow. A. AUTOMATIC - A firearm design that feeds cartridges, fires, extracts and ejects cartridge cases as long as the trigger is fully depressed and there are cartridges in the feed system. Also called FULL AUTO and MACHINE GUN. B. BOLT - A firearm in which the breech closure: (1) is in line with the bore at all times (2) manually reciprocates to load, unload and cock, (3) is locked in place by breech bolt lugs and engaging abutments usually in the receiver. There are two principal types of bolt actions: the turn bolt and the straight pull. C. BOX LOCK - A design in which the hammer and hammer springs are located within the frame and the trigger assembly in the lower tang. Generally found on double barrel shotguns such as Parker, Fox, Stevens, Winchester Models 21 and 24, etc. D. FALLING BLOCK - A single shot lever action mechanism. The breechblock slides vertically or nearly vertically, when the lever is moved, to expose or lock the breech. Example: Ruger No. 1. E. HINGED FRAME - A design wherein the barrel(s) is pivoted on the frame. When the action is open, the barrel (2) 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. F. LEVER - A design wherein the breech mechanism is cycled by an external lever generally below the receiver. G. MARTINI - A hammerless single shot rifle action, lever operated, in which the movement of the breechblock is entirely within the receiver and pivots at the rear. H. REVOLVER - A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis and be discharged successively by the same firing mechanism. See also REVOLVER. I. ROLLING BLOCK - A single shot action 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. Example: Remington No. 4. J. SEMIAUTOMATIC - A repeating firearm requiring 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 (usually the loading portion). K. SIDELOCK - A design in which the firing mechanism is attached to a sideplate rather than being integral with the frame. L. SLIDE - An action which features a movable forearm which is manually actuated in 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. M. TRAP DOOR - 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. Also known as a CAM LOCK.
Semiautomatic Action
The working mechanism of a firearm. May be broken down into action types as follow. A. AUTOMATIC - A firearm design that feeds cartridges, fires, extracts and ejects cartridge cases as long as the trigger is fully depressed and there are cartridges in the feed system. Also called FULL AUTO and MACHINE GUN. B. BOLT - A firearm in which the breech closure: (1) is in line with the bore at all times (2) manually reciprocates to load, unload and cock, (3) is locked in place by breech bolt lugs and engaging abutments usually in the receiver. There are two principal types of bolt actions: the turn bolt and the straight pull. C. BOX LOCK - A design in which the hammer and hammer springs are located within the frame and the trigger assembly in the lower tang. Generally found on double barrel shotguns such as Parker, Fox, Stevens, Winchester Models 21 and 24, etc. D. FALLING BLOCK - A single shot lever action mechanism. The breechblock slides vertically or nearly vertically, when the lever is moved, to expose or lock the breech. Example: Ruger No. 1. E. HINGED FRAME - A design wherein the barrel(s) is pivoted on the frame. When the action is open, the barrel (2) 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. F. LEVER - A design wherein the breech mechanism is cycled by an external lever generally below the receiver. G. MARTINI - A hammerless single shot rifle action, lever operated, in which the movement of the breechblock is entirely within the receiver and pivots at the rear. H. REVOLVER - A firearm, usually a handgun, with a cylinder having several chambers so arranged as to rotate around an axis and be discharged successively by the same firing mechanism. See also REVOLVER. I. ROLLING BLOCK - A single shot action 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. Example: Remington No. 4. J. SEMIAUTOMATIC - A repeating firearm requiring 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 (usually the loading portion). K. SIDELOCK - A design in which the firing mechanism is attached to a sideplate rather than being integral with the frame. L. SLIDE - An action which features a movable forearm which is manually actuated in 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. M. TRAP DOOR - 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. Also known as a CAM LOCK.
Action
The working mechanism of a firearm. May be broken down into action types.
Blowback, Simple
This system in its simplest form allows 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 coming back during its period of peak pressure. Example: 22 rimfire semiautomatic rifles or pistols.
Discharge
To cause a firearm to fire.
Extractor Mark
Toolmarks produced upon a cartridge or cartridge case from contact with the extractor. These are usually found on or just ahead of the rim.
1F
coarse, for .69 to .75 caliber muskets
4F
extra-fine, only for priming flintlock arms
3F
fine, for .31 to .45 caliber rifles and most handguns
2F
medium, for .45 to .58 caliber rifles and muskets