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