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