Module 10 - terms

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.

bore diameter

In rifled barrels the minor diameter of a circle formed by the tops of the lands. In shotguns or muskets, the interior dimensions of the barrel forward of the chamber but before any restrictive choke or expanded muzzle.

armor piercing bullets

a bullet consisting of a hardened core or wholly composed of a substance other than lead lead alloy any bullet manufactured, represented, or designed to be metal or armor piercing

incendiary bullet

a bullet containing a chemical compound which ignites upon impact to start fires

exploding bullet

a bullet containing a primer or other explosive and designed to explode upon impact

Spitzer bullet

a bullet design having a sharp point, long ogive, usually of seven calibers or more

lead bullet

a bullet formed by a lead alloy

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

jacketed bullets

a bullet having an outer jacket and containing a lead alloy core

tracer bullet

a bullet that has a burning compound in its base which permits observation of its flight

swaged bullet

a bullet that has been formed by compressing and forming the bullet material in a die

hollow base bullet

a bullet with a deep base cavity

semijacketed hollow point bullet

a bullet with a partial jacket exposing a lead nose with a cavity

flat-nosed bullet

a bullet with flattened tip at right angles to its axis

known standards

a collection and cataloging of test-fired bullets and cartridge cases from known firearms

conical/conoidal bullet

a cone-shaped bullet

wadcutter bullet

a cylindrical bullet design having a sharp-shouldered nose intended to cut target paper cleanly to facility easy and accurate scoring

truncated bullet

a design of a flat-nosed bullet having a conical, rather than rounded, nose

soft point bullet

a design providing for exposure of a portion of the core at the nose of a jacketed bullet

firearm 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

reticule

a grid or pattern of posts or lines placed in the focus of a lens which establishes a frame of reference for the measurement of distance or the position of objects viewed through the lens; may consist of intersecting or parallel lines, lines etched into glass, a post or multiple posts, a pinhead dot or any combination of wires, dots, and posts of varying sizes and thickness

gas check bullet

a lead alloy bullet with a copper or gilding metal cup pressed over the base

sabot

a lightweight carrier in which a subcaliber projectile(s) is centered to permit firing an enclosure to facilitate the firing of shot usually in a rifled barrel

shot collar

a plastic or paper insert surrounding the shot charge in a shotshell to reduce distortion

wad

a plastic, paper, or fiber disk used to keep ammunition components in place or separated

cup wad

a powder and shot separator of very shallow cup design, which when loaded with lips down acts to help seal powder gases and so protect the rear of the shot column

frangible bullets

a projectile designed to disintegrate upon impact with a hard surface in order to minimize ricochet

full metal jacket bullet

a projectile in which the bullet jacket encloses the entire bullet, with the usual exception of the base

semiwadcutter bullet

a projectile with a distinct, short truncated cone at the forward end

cartridge

a single unit of ammunition consisting of the case, primer, and propellant with one or more projectile(s)

slug

a term applied to a single projectile for shotshells

washed bullet

a term used for lead bullets with a coating; found extensively on 22 rimfire cartridges.

card wad

a thin card-like disc used in shotshells as overshot wad, undershot wad, and over-powder wad

round nose bullet

an elongated projectile with a radiused nose; the radius of the nose is one-half of the bullet's diameter

Nyclad

an inert nylon jacketing or coating on a lead bullet; a Smith and Wesson original trade name which has been purchased by Federal Cartridge Corporation

ultrasonic cleaner

an instrument used to clean objects submerged in a detergent or other solution by agitation from high-frequency sound waves

micrometer

an instrument used to measure accurately small distances, usually thickness or diameter

projectile

an object propelled by the force of rapidly burning gases or other means

stereomicroscope

an optical instrument, which provides three dimensional viewing of an object through paired objectives and eyepieces

meplat

blunt tip of some bullets, specifically the diameter of that blunt tip

filler wad

circular disc of various thickness used to adjust the volume of the contents of a shotshell

cannelure

circumferential groove in a bullet generally of a knurled or plain appearance for the purpose of lubrication or identification, or to assist in crimping a bullet in the mouth of a cartridge case

solid base bullet

composed of one material with no jacketing

heel

configuration of the intersection of the bearing surface and base of a bullet

metal point (capped) bullet

consists of a standard lead bullet having a harder metal jacket over the nose

striations (striae)

contour variations, generally microscopic, on the surface of an object caused by a combination of force and motion where the motion is approximately parallel to the plane being marked

ogive

curved forward part of a bullet nose

tip

extreme forward end of a bullet

nose

forward end of a bullet, including the tip, the ogive, and meplat (if present)

total metal jacket

fully encloses a bullet core

grooves

helical grooves in the bore of a firearm barrel to impart rotary motion to a projectile

jacketed solid base

jacketed bullet with the core enclosed

open base bullet

jacketed bullet with the core exposed

polygonal rifling

lands and grooves having a rounded profile instead of the traditional rectangular profile

coated (plated) bullet

lead alloy bullet having a thin metal alloy coating

coated bullet

lead alloy bullet having a thin metal alloy coating

buckshot

lead pellets ranging in size from .20" to .36" diameter normally loaded in shotshells

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; unique to that tool and distinguish it from all other tools

class characteristics

measurable features of a specimen which indicates a restricted group source; result from design factors, and are therefore determined prior to manufacture

gilding metal

metal alloys of 90 or 95 percent copper adn the remainder zinc

metal fouling

metallic bullet material left in the bore after firing

bullet

non spherical projectile for use in a rifled gun barrel

combination wad

one piece of multipiece plastic wad which may combine the following items: shot protector, filler wad, and overpowder wad

marketer

one that promotes or sells a product or service

bearing surface

portion of the outer surface of a bullet that makes direct contact with the interior surface of a gun barrel

cast

pouring molten metal into a mold to produce an object of desired shape

base

rear portion of a bullet

skid marks (slippage)

rifling marks formed on the bearing surface of bullets at they enter the rifling of the barrel before rotation of the bullet starts; typically produced by revolvers and have the appearance of widening of the land impressions at their beginning point

microscopic marks

striae or patterns of minute lines or grooves in an object; in firearm and toolmark identification, these marks are characteristic of the object which produced them and are the basis for identification

leading

the accumulation of lead or bullet jacket material in the bore of a firearm from the passage of lead shot or bullets

mushrooming

the act of expansion of a bullet upon impact with a target

crimping

the closure of the mouth of a shotshell by one of a number of crimping techniques

shaving (shearing)

the cutting of metal from a bullet due to cylinder misalignment in a revolver

ricochet

the deflection of a projectile(s) after impact.

bullet penetration

the distance which a bullet travels in a target material

blowby

the escaping of gases past the bullet, while the bullet is in the barrel

primer

the ignition component of a cartridge

bullet core

the inner portion of a jacketed bullet, usually lead

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

land and groove impression

the negative impressions on the bearing surface of a bullet caused by the rifling in the barrel from which it was fired

land and groove impressions

the negative impressions on the bearing surface of a bullet caused by the rifling in the barrel from which it was fired

general rifling characteristics (GRC)

the number, width, and direction of twist of the rifling grooves in a barrel of a given caliber firearm

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

cylinder

the rotatable part of a revolver that contains the chambers

obturation

the sealing of gases due to the expansion and/or upset of the bullet base as it travels down the bore

extrusion

the slow forcing of material under high pressure through a die to reduce its diameter; this process is generally performed in a hydraulic press

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

shot protector wad

various designs of shot cups made of plastic and designed to reduce pellet deformation during barrel travel

firing

when the breech is fully locked, a pull on the trigger mechanically translates to the firing pin release

controlled expansion

when the first chamber of a jacketed bullet expands and the rear chamber holds together for penetration