Glossary of Terms

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The overall mechanism by which a gun loads, discharges and unloads, encompassing the action of all component parts. Typically, firearms are single-action or double-action. For single-action operation, the user must manually cock the hammer; double-action operation automatically cocks and releases the hammer by way of the trigger.

Action, Automatic

A type of firing action that delivers continuous loading, firing, and cartridge ejection while the trigger is depressed. These firearms use magazines to deliver ammunition to the chamber. Machine guns employ automatic action. Possession of an automatic firearm (i.e. machine guns) requires special permission and licensing through the U.S. Department of the Treasury.

Action, Bolt

A type of firing action that requires manual loading, hammer-cocking, and unloading. Unloading and loading is done by retracting the bolt mechanism, which ejects the used cartridge and allows for the insertion of another. Many rifles employ bolt action. Bolt action delivers good accuracy, which makes them popular for hunting and many shooting sports.

Action, Lever

Similar to bolt action, this mechanism uses an external lever, most often found directly below the receiver, to load new cartridges, cock the hammer, and unload spent cartridges. Many rifles use lever action.

Action, Pump

This firing mechanism employs a sliding forearm that, with a single pump, chambers a new round and ejects the spent round. Once the forearm has been pumped, no cocking is required for the next discharge. Many shotguns use pump action.

Action, Semi-automatic

Firing mechanism used on self-loading firearms. Delivers a complete firing cycle, including loading, firing, and discharging of the spent cartridge, with each depression of the trigger. This action is achieved through blowback-, recoil-, or gas-operation. This differs from fully automatic firearms, which will continue the firing cycle as long as ammunition is ready and the trigger is depressed. Semi-automatic firearms are also known as “self-loading” or “auto-loading” firearms.


All-encompassing term referring to ready, encased projectiles for use with firearms. Generally consists of a case, powder (or other propellant), projectile, and primer. Includes bullets, shotgun shells, cartridges, etc.

Ammunition, Small Arms

Referring to ammunition measuring smaller than 1 inch and designated for use with barrel interiors (also known as bores) of equal to or less than 1 inch in diameter. Primarily a military term, though increasingly used in a general sense.

Arms, Small

Technically any firearm with a bore (barrel interior) measuring 1 inch or less in diameter. Also refers to any standalone firearm that can be carried and discharged by a single person with no additional equipment.


Scientific field dedicated to the physics of projectile launch and projectiles in motion. In reference to firearms, ballistics is sub-divided into interior, exterior, and terminal ballistic categories. Interior ballistics focuses on movement inside the firearm; exterior focuses on movement through the air; and terminal focuses on movement through the target. Ballistic-expert forensic scientists use their knowledge to match bullets and cartridges with the “signatures” of individual firearms.


The section of a firearm, comprised of bore and chamber, through which a projectile travels. Projectiles are propelled through the barrel via the action of burning powder. Rifled barrels refer to barrels with grooves machined in a spiral pattern along the interior, while smooth-bore barrels have no grooves.


Generally refers to any spheroid shot measuring .175-inches in diameter. Specifically, the small diameter (.180-inch) spheroid shot that makes up the load of a shotgun shell. Single-shot BBs are the shot used with BB guns.


A specialized, stable stand, platform, or table used by a shooter to support the limbs and body and steady the aim. Used for benchrest rifle shooting, as well as for sighting-in and testing accuracy. Also refers to the rifle-shooting sport that incorporates benchrests in competition.

Big Bore

General term referring to ammunition for handguns higher than .38 caliber and rifles .30 caliber and higher. Also used in the United Kingdom in reference to rifles .40 caliber and higher.


Type of shotgun shot (usually loaded into shotshells) consisting of small pellets (less than .10 inches in diameter) fashioned from lead or steel. Intended for bird and small-game hunting.


The interior portion of the barrel, not including the chamber; may be smooth or rifled.

Bore Diameter

The diameter of a gun barrel’s interior. With rifled barrels, this is measured from the highest point of the spiraled grooves.


Type of shotgun shot (usually loaded into shotshells) consisting of large lead pellets, ranging .20 to .36 inches in diameter. Intended for deer and large-game hunting.


A non-spherical projectile, usually made of lead, designed to be fired from rifled barrels. Sometimes covered with a metallic jacket.

Bullet, Armor Piercing

Firearm projectile designed to penetrate armor. Those designed for handguns and other small arms are constructed of hardened steel or with a combination core construction of metal alloys. The manufacture and sale of armor piercing bullets for non-military and law enforcement use is prohibited by The Gun Control Act of 1968.

Bullet Engraving

The “signature” or unique imprints left upon the bullet by the bore of a gun as it is discharged from the firearm. Forensic experts use these markings to match fired bullets to the guns from which they were fired.

Bullet, Full Metal Jacket

A bullet with a metallic casing (usually copper) over its exterior, covering all but the base. Used primarily for target shooting and military applications. Round-nose bullets are often described as full metal jacket bullets.

Bullet, Hollow Point

A type of bullet designed to expand upon impact, lessening the overall depth of penetration. This is done by creating a cavity in the nose of the bullet, exposing the core. These cartridges are typically used by law enforcement for self-defense and by hunters to avoid overpenetration.

Bullet, Wadcutter

Bullet designed for target shooting. Its cylinder shape and pointed nose cleanly perforate target paper, leaving behind clear, identifiable entry points ideal for precise scoring.


The rear end of a firearm, opposite the muzzle. This is the bottom portion of the handle on handguns, and the end of the stock on shotguns and rifles.


Refers to the bore diameter of a firearm or to the name of a particular cartridge, which offers an approximation of the bullet diameter. The caliber of a rifled barrel refers to a measurement taken from the tops of the grooves.


A general term for rifles with short, lightweight frames originally designed to accommodate cavalry.


A round of ammunition, usually with a primed case, powder (or other propellant), and one or more projectiles as its component parts. Usually refers to the ammunition of a pistol or rifle.

Cartridge, Centerfire

A complete, single round of ammunition with the primer portion situated at the case head. Most cartridges are of the centerfire variety.

Cartridge, Magnum

A specially designed cartridge producing greater projectile velocity, or a shotshell containing more shot, than the standard for any given firearm.

Cartridge, Rimfire

A complete, single round of ammunition with the primer located within the metal rim of the casing. The common .22 rifle uses rimfire cartridges.

Cartridge, Small Bore

Also known as rimfire cartridges, such as those used with .22 caliber rifles.


Rearward portion of the barrel of a firearm that encapsulates the ammunition, typically where the cartridge is loaded. This part of the barrel prevents expansion of the case as the propellant ignites.


The narrowed portion of the forward end of a shotgun muzzle. Designed to control the dispersion pattern, or spread, of the shot as exits the muzzle. Common choke types include cylinder, improved cylinder, modified, and improved modified. Cylinder chokes result in a broad spread, while full chokes create a much more concentrated spread. Type of shooting, shot size, and other factors determine which type of choke is ideal.


A cartridge-holding device that keeps the cartridges together for easy loading into the firearm. Also referred to as chargers or en bloc clips. Not to be confused with a Magazine.


The act of retracting the hammer of a firearm into its locked position, in which it is ready for firing.


The cylinder-shaped portion of a revolver that holds cartridges in its chambers and rotates to give this firearm its name. Each rotation positions the next cartridge in line for firing.


General term for a compact, pocket-size pistol with a capacity of one or two rounds.


The act of igniting an ammunition cartridge with a firearm.

Double Barrel

A type of firearm whose design incorporates two barrels, whether configured side-by-side or over-under, within a single frame.


Generally, any device that employs an ignited charge to launch a projectile.

Firing Pin

A firearm component forced into the primer of a cartridge by the force of the hammer, resulting in a controlled explosion that launches the projectile. A spring driven firing pin on guns with no hammer such as the Glock is called a Striker.

Flash Suppressor

An accessory that attaches to the muzzle of a firearm and disperses the ignited gases in order to restrain muzzle flash.

Full Cock

Refers to the hammer fully retracted into firing position; a pistol ready for firing.


System of measurement referring to the bore diameter of a smooth-bore firearm based on the weight of the largest lead ball that the firearm can discharge. The lone exception to this is the .410 shotgun, which refers directly to the diameter of the barrel (caliber).


The resulting pattern of bullets fired at a target in succession without changing the aiming point; often used to determine performance accuracy and adjust sighting.

Hair Trigger

A trigger that requires a relatively small amount of force to depress. Often used for target practice for more consistent aim and steady repeated shooting.

Half Cock

A safety notch built into the hammer, which clicks into place at the halfway point. Intended to prevent unintended dropping of the hammer.


Specific firearm design in which the hammer or striker is integrated into the gun’s interior.


The hard metal casing that encapsulates a bullet’s softer metal core.


A generic term referring to any firearm malfunction involving failure of moving parts, faulty ammunition, poor maintenance, or misuse.


In rifled barrels these are the threads, or raised portions in relation to the grooves.


A general term referring to the all the component parts of a cartridge. Also, the act of placing ammunition in the chamber of a firearm.


A cartridge-holding device which can be detachable or an integral part of the firearm. Various magazine designs hold anywhere from two cartridges or shells to multiple dozens and deliver them directly to the chamber for firing. Box, tubular, drum, and rotary are common magazine types.


See Cartridge, Magnum


A failure to load a live cartridge into the chamber during normal operation of a repeating firearm. Also known as failure to chamber or failure to feed.


A malfunction of the primer of a round of ammunition when struck by the firing pin, resulting in fire failure to fire.


The forward-most section of the barrel of a firearm; it is from here that the bullet or shot is projected.

Muzzle Flash

The brief, intense flaring of ignited, expanding gases that emerge from the end of the barrel and react with the oxygen in the air when a firearm discharges.

Muzzle Loader

Any traditional firearm loaded by inserting a powder charge along with the bullet or shot through the muzzle. Also known as a black powder guns.


The forward tip, usually a narrow point, of a bullet or other projectile.

Over and Under

A double barrel firearm with the two barrels arranged in a vertical configuration. Typically an over and under shotgun.


The arrangement or spread of shot when fired from a shotgun. General measurements are derived from the percentage of pellets that terminate in a 30-inch target area situated 40 yards from the point of discharge.


A single-chamber, non-revolving, hand-held firearm.

Pistol, Automatic

Almost always the term used to denote a semi-automatic or auto-load/self-load pistol. Though rare, fully automatic pistols do exist. Semi-automatic pistols are markedly more common. See Action, Semi-Automatic.

Pistol, Double Action

A form of pistol operation that cocks and drops the hammer with a single depression of the trigger.

Pistol, Single Action

A from of pistol operation in which the user must fully cock the hammer manually before the trigger can start the firing reaction.


Leisurely shooting at inanimate objects such as cans or bottles for general target practice or entertainment.


Small particles of combustible matter that, when ignited, serves to propel the bullet or shot from the barrel of a firearm. Also a general term for any propellant, including gases.

Powder, Black

The earliest known form of firearm propellant, originating in Asia in the 13th century and comprised of potassium nitrate, charcoal, and sulfur. This mixture reacts in a brief, bright flash resulting in a cloud of dark smoke when ignited.

Powder, Smokeless

A modern, non-corrosive firearm propellant containing nitrocellulose, which results in very little smoke when ignited.


The rapid buildup of force resulting from the expanding gases caused by the ignition and combustion of the propellant.


compartment of a cartridge containing a combustible material which, when struck with the firing pin, creates the spark that ignites the propellant.


The chemical compound or mixture whose reactionary products are rapidly expanding gases, which propel the bullet or shot when ignited by the primer spark. See also, Powder.


The frame or action body portion of a firearm in which lies the firing mechanism. This part joins the barrel and the stock. Also called the frame in break-open firearms.


The forced rearward motion of a firearm caused by the expanding gases exiting the muzzle during the firing of a bullet or shotshell. Also known as kickback.

Recoil Pad

A cushioned panel made from rubber, leather, cloth, or synthetic materials that is affixed to the butt end of a firearm in order to lessen the impact of recoil or kickback action against the shoulder.


The act of setting a cartridge directly into the chamber of a firearm or into a magazine after a cartridge or magazine has been emptied. Reloading also refers to the process of fashioning a new round of ammunition from fired cases and component parts in order to customize the ammunition to suit specific purposes.


A type of handgun with a rotating cylinder which houses several chambers that rotate on an axis so that the firearm can be fired repeatedly until all the chambers are empty. Chambers typically number between 5 and 10.


Refers generally to long shoulder-fired firearms featuring spiraled grooves along the length of the barrel interior (bore). These grooves cause the projectile to rotate as it moves through the air for improved range and accuracy. Many handguns also employ rifled barrels.


Refers to the spiral grooves along the length of the bores of rifles and handguns. Also refers to the process of machining such grooves. See also, Rifle.


Integral mechanisms of a firearm intended to prevent accidental firing. Push-button, sliding, and lever are three common safety designs.


General term for the mechanism employed by self-/auto-loading firearms, which deliver a complete firing cycle, including firing, ejection, and reloading of a new cartridge with each trigger depression. See also, Action, Semi-automatic.


A long, shoulder-fired firearm with a smooth bore interior which facilitates the discharge of numerous pellets, or shot, in a consistent pattern. Some models are capable of firing single slug projectiles.


A complete round of shotgun ammunition consisting of multiple pellets (shot), propellant, primer, and casing. Also known as a shotgun shell.


Shotgun target sport in which shooters attempt to hit disc-shaped clay targets, which are launched into a specified range in front of them. Also known as skeet shooting.

Skeet Gun

A specific shotgun designed for use in skeet target shooting. This shotgun uses an open choke at the muzzle to create a specific shot pattern for shooting targets.

Sporting Clays

Shotgun target sport in which shooters fire at disc-shaped clay targets launched from a series of stations over different types of terrain.


The near-end portion of a long firearm, usually made from wood or synthetic material, which is connected to the receiver and barrel. This portion is supported by the shooter’s body to steady his aim.


A firearm attachment that fits onto the muzzle with the purpose of suppressing the noise that results from rapidly expanding gases breaking the sound barrier. Also known as a silencer.

Target, Clay

A disc, fashioned from clay, used as a target in a variety of shotgun-shooting sports. These are usually launched into the air using a device called a trap. Shapes, sizes, and colors vary based on sport regulations or preference. Also known as clay pigeons.


The curved path taken by a projectile over the course of its flight.


The device used to launch a clay target. These can be gas-, electricity-, or hand-powered.

Trap Shooting

Shotgun target sport in which multiple clay targets are launched simultaneously outward from a single trap situated in front of the shooter.

Trigger Lock

A safety accessory that inhibits depression of the trigger. These are recommended for use with unloaded firearms, as removing the lock can apply force to the trigger.

Trigger Pull

The amount of force required to fully depress the trigger of a firearm, expressed in pounds. This force can vary widely, with target firearms requiring about 1 pound of pressure and double-action firearms requiring about 15 pounds or more.


The act of removing all ammunition from a firearm or magazine. Can also refer to emptying the firearm entirely by firing.


The rapidity of motion or speed of an occurrence. In physics, defined as the rate of change of the position of a body in a specific direction. The standard unit is feet per second.


Shotshell component that serves to separate the propellent from the pellets. Typically a plastic column or series of paper discs.


Any implement used to attack or defend in combat or assault situations. This term generally does not apply to sporting firearms, which are not employed in such fashion.