Unit 6: Firearms
rimfire
a cartridge with the primer distributed around the periphery of the base.
choke
a constriction of a shotgun bore at the muzzle that determines the pattern of the fired shot
magazine
a device for storing cartridges in repeating firearm for loading into the chamber. Also referred to as a "clip"
silencer
a device that fits over the muzzle of the barrel to muffle the sound of a gunshot. Most work by baffling the escape of gases.
semi-automatic
a firearm that fires a projectile each time the trigger is pulled until out of ammunition
automatic
a firearm that will begin to fire projectiles as soon as the trigger is pulled and continue to fire until the trigger is released or it has run out of ammunition
rifle
a firearm, usually two or more feet in length, designed to be fired from a shoulder-held position
shotgun
a gun with a smoothbore that shoots cartridges that contain "shot" or small metal pellets (of lead or steel) as the projectiles
toolmark
a marking on a surface caused by the pressing or sliding of a tool into or across the surface
safety
a mechanism to prevent firing of the gun
hammer
a metal rod or plate that strikes the cartridge primer to detonate the powder
powder pattern
a pattern found on an object close to the barrel of a fired weapon caused by small particles of lead, or partially burned gunpowder and carbon smoke that follow the projectile out of the barrel
slug
a single projectile used in a shotgun shell instead of pellets, analogous to the bullet in the handgun or rifle cartridge
primer
a volatile substance that ignites when struck to detonate the powder in a cartridge
stock
a wood, metal, or plastic frame that holds the barrel and action and allows the gun to be held firmly
cartridge
also called, "round", "ammunition", or "shell" . Made up of a case, primer, powder, and bullet.
magnum
an improved version of a standard cartridge which uses the same caliber and bullet, but has more powder, giving the fired bullet more energy. Magnum shotgun loads, however, refer to an increased amount of shot pellets in the shell
revolver
handgun that has a cylinder with holes to contain the cartridges. The cylinder revolves to bring the cartridge into position to be fired. Can be single-action or double-action.
lands and grooves
lands are the metal inside the barrel left after the spiral grooves are cut to produce the rifling
gunshot residue (GSR)
materials created by the firing of a firearm that are dispersed by the force of the expanding gases
powder
modern gun cartridges use "smokeless" powder that is relatively stable, of uniform quality, and leaves little residue when ignited.
double-action
pulling the trigger both cocks the hammer and fires the gun
smokeless powder
refers to modern gunpowder, which is really not "powder" but flakes of nitrocellulose and other substances. Not really "smokeless" but much less so than black powder.
gauge
refers to the diameter of the barrel on a shotgun, in terms of the number of lead balls the size of the bore it would take to weigh on pound (10 gauge, 12 gauge, etc).
pistol/handgun
synonym for a handgun that does not have a revolving cylinder
centerfire
the cartridge contains the primer in the center of the base, where it can be struck by the firing pin of the action (most commonly on a 22)
land impressions
the depressed helical grooves in a bullet left by the lands inside the barrel from which it was fired
sights
the device(s) on top of a barrel that allow the gun to be aimed
caliber
the diameter of the bore measured from land to land, usually expressed in hundredths of an inch (.22 cal) or millimeters (9mm)
breech
the end of the barrel attached to the action
muzzle
the end of the barrel out of which the bullet exits
round-nose bullet
the end of the bullet is round
wad cutter bullet
the front of the bullet is flattened. Used mainly for target practice.
single-action
the hammer must be manually cocked before the trigger can be pulled
firing pin impression
the impression left by the firing pin on the primer cup portion of a cartridge after it has been struck (fired)
bore
the inside of the barrel. "Smoothbore" weapons have no rifling. Most handguns and rifles have "rifling"
barrel
the metal tube through which the bullet is fired
NIBIN
the national database primarily of images of cartridge cases used to try to associate evidence cases with test-fired cases from seized weapons or cases collected from shooting incidents where the gun involved is not known
black powder
the old form of gunpowder invented over a thousand years ago and consisting of nitrate, charcoal, and sulfur
Action
the part of a firearm that loads, fires, and ejects a cartridge. Includes lever action, pump action, bolt action, and semi-automatic.
chamber
the portion of the "action" that holds the cartridge ready for firing
butt or stock
the portion of the gun, which is held or shouldered
bullets
the projectile. they are shaped or composed differently for a variety of purpose
1/2 jacketed bullet
the soft lead is partially surrounded by another metal, usually copper, that promotes exit velocity
rifling
the spiral or helical grooves cut inside a gun barrel that gives the bullet a spinning motion
breech face
the surface of the firearm, usually machined, against which the cartridge case is forced by the expanding gases as a result of being fired
ignition
the way in which powder is ignited. Old muzzle-loading weapons used flintlock or percussion caps. Modern guns use "primers" that are "rimfire" or "centerfire"
hollow-point bullet
there is a hole in the bullet that creates expansion when a target is struck, creating more damage
double barrel
two barrels side by side or one on top of the other, usually on a shotgun
firearms comparison microscope
two reflected-light microscopes linked with an optical bridge used for comparison of objects using reflected light