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ACTION

The combined parts of a firearm that determine how a firearm is loaded, discharged and unloaded. Most handguns are referred to as "single-action" or "double-action." A single-action firearm requires the user to manually pull back the hammer before the firearm allows the user to either manually cock the hammer or simply pull the trigger and allow the firearm to cock and release the hammer on its own.

ACTION, AUTOMATIC

A firearm that loads, fires, and ejects cartridges as long as the trigger is depressed and there are cartridges available in the feeding system (i.e. magazine or other such mechanism). Automatic action firearms are machine guns. Note: Since 1934 it has been unlawful to sell or possess an automatic firearm without special permission and licensing from the U.S. Department of the Treasury, in addition to other measures.

ACTION, BOLT

A firearm, typically a rifle, that is manually loaded, cocked, and unloaded by pulling a bolt mechanism up and back to eject a spent cartridge and load another. Bolt action firearms are popular for hunting, target shooting, and biathlon events. A bolt action rifle allows the shooter maximum accuracy, but may be too slow or cumbersome for some shooting sports.

ACTION, LEVER

A firearm, typically a rifle, that is loaded, cocked, and unloaded by an external lever usually located below the receiver. Note: The type of rifle used in most Western movies is a lever-action.

ACTION, PUMP

A firearm that features a movable forearm that is manually actuated to chamber a round, eject the casing, and put another round in position to fire.

ACTION, SEMI-AUTOMATIC

A firearm in which each pull of the trigger results in a complete firing cycle, from discharge through reloading. It is necessary that the trigger be released and pulled for each cycle. These firearms are also called "autoloaders" or "self-loaders." The discharge and chambering of a round is either blowback operated, recoil operated, or gas operated. Note: An automatic action firearm loads, discharges, and reloads as long as ammunition is available and the trigger is depressed. A semi-automatic firearm only discharges one cartridge with each squeeze of the trigger.

AMMUNITION

A loaded cartridge consisting of a primed case, propellant, and a projectile. Among the many types of ammunition are centerfire rifle and pistol, rimfire, shotshells, and reloads.

AMMUNITION, SMALL ARMS

A military term used to describe ammunition for firearms with bores (the interior of the barrel) not larger than one inch in diameter.

ARMS, SMALL

Any firearm capable of being carried by a person and fired without additional mechanical support.

ARMOR PIERCING

See BULLET, ARMOR PIERCING

BALLISTICS

The science of studying projectiles. Ballistics can be "interior" (inside the gun), "exterior" (in the air), or "terminal" (at the point of impact). Ballistic comparison is the attempt to microscopically match a bullet or fired cartridge case to a particular firearm.

BARREL

That part of a firearm through which a projectile travels. The barrel may be rifled (i.e., with spiral grooves on the interior of the barrel) or smooth bore (i.e., a smooth interior barrel with no grooves).

BB

Spherical shot having a diameter of .180" used in shotshell loads. The term is also used to designate steel or lead air rifle shot of .175" diameter.

BENCHREST

A table specifically designed to eliminate as much human error as possible by supporting a rifle for competitive shooting or sighting-in purposes.

BIG BORE

In America, any firearm using a centerfire cartridge with a bullet .30" in diameter or larger.

BIRDSHOT

Small lead or steel pellets used in shotshells ranging in size from #12 (less than the diameter of a pencil point) to #4 (about .10" in diameter) used for short-range bird and small game hunting.

BORE

The interior barrel forward of the chamber.

BORE DIAMETER

On rifled barrels, the interior diameter of the barrel from the tops of the lands (the highest point of the grooves). On a smooth barrel, the interior dimension of the barrel forward of the chamber (not including the chose on the shotgun barrels).

BUCKSHOT

Large lead pellets ranging in size from .20" to .36" diameter normally loaded in shotshells used for deer hunting.

BULLET

A non spherical projectile for use in a rifled barrel.

BULLET, ARMOR PIERCING

A projectile or projectile core that may be used in a handgun intended to pierce steel armor that is constructed entirely, or has a core constructed, from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, depleted uranium, or a fully jacketed projectile larger than 22 caliber intended for use in a handgun whose jacket has a weight of more than 25 percent of the total weight of the projectile. The term does not include shotgun shot or projectiles intended for sporting purposes. Note: The Gun Control Act of 1968 (18 U.S.C. Sec. 922 (a) (7)) prohibits the manufacture of sale of armor piercing ammunition, except for use by law enforcement and the military.

BULLET, DUMDUM

A British military bullet developed in India's Dum-Dum Arsenal in 1897-98. It was a jacketed .303 caliber rifle bullet with the jacket most left open to expose the lead core in hopes of greater effectiveness. Further development of the bullet was not pursued because the Hague Convention of 1899 outlawed and such bullets for warfare.

BULLET ENGRAVING

The grooves cut into a bullet by barrel rifling. Note: When a bullet travels down the barrel, the grooves (or rifling) leave an imprint on the bullet. The matching of the marks on a bullet to the rifling of a particular firearm is an important tool for law enforcement in determining whether a bullet was fired from a particular firearm.

BULLET, FULL METAL JACKET

A projectile in which the bullet jacket (a metallic cover over the core of a bullet) encloses most of the core with the exception of the base. They are used mostly for target shooting and military use.

BULLET, HOLLOW POINT

A bullet with a cavity in the nose, exposing the lead core, to facilitate expansion upon impact. Hollow point cartridges are used for hunting, self-defense, police use, and other situations to avoid over penetration.

BULLET, WADCUTTER

A generally cylindrical bullet design having a sharp shouldered nose intended to cut paper targets cleanly to facilitate easy and accurate shooting.

BUTT

On handguns, it is the bottom part of the grip. On long guns, it is the rear or shoulder end of the stock.

CALIBER

A term used to designate the specific cartridges for which a firearm is chambered. It is the approximate diameter of the circle formed by the tops of the lands of a rifled barrel. It is the numerical term included in the cartridge name to indicate a rough approximation of the bullet diameter (i.e. .30 caliber- .308" diameter bullet).

CARBINE

A rifle of short length and light weight originally designed for horse-mounted troops.

CARTRIDGE

A single round of ammunition consisting of the case, primer, propellant, powder, and one or more projectiles.

CARTRIDGE, CENTERFIRE

Any cartridge intended for use in rifle, pistols, and revolvers that it has its primer central to the axis at the head of the case. Note: Most cartridges, including shotshells, are centerfire with the exception of 22 caliber rimfire ammunition. If you were to look at the bottom of a centerfire cartridge, you would see a small circle in the middle of the base, hence, "centerfire." There are a few rimfire ammunition calibers besides the 22, but they are rare and not widely available.

CARTRIDGE, MAGNUM

Any cartridge or shotshell that is larger, contains more shot, or produces a high 46 velocity than standard cartridges or shotshells of a given caliber or gauge.

CARTRIDGE, RIMFIRE

A cartridge containing the priming mixture in the rim of the base, usually a 22.

CARTRIDGE, SMALL BORE

A general term that refers to rimfire cartridges. Normally 22 caliber ammunition used for target shooting, plinking, and small game hunting.

CHAMBER

In a rifle, pistol, or shotgun, it is the part of a barrel that accepts the ammunition. In a revolver, it refers to the holes in the cylinder where the cartridges are loaded.

CHOKE

An interior tube at the end of a shotgun barrel that controls shot dispersion. Chokes typically come in cylinder, improved cylinder, modified, improve modified, and full. Note: A cylinder choke produces a very wide shot dispersion, whereas a full chose will provide a much tighter shot pattern. Different chokes are used for skeet, trap, and sporting clays. In hunting, the type of game and conditions will determine choke type.

CLIP

See MAGAZINE.

COCK

To place the hammer, or striker, in position for firing by pulling it back fully.

CYLINDER

The round, rotatable part of a revolver that contains the cartridge chambers.