ACP – An abbreviation meaning: Automatic Colt Pistol. It is commonly used to designate specific calibers, particularly those which were originally designed by John Moses Browning for the Colt Firearms Company. Automatic Colt Pistol, a type of ammunition. For example: as in .45 ACP, .380 ACP, and .25 ACP
ACTION – The working mechanism of a firearm involved with presenting the cartridge for firing, and in removing the spent casing and introducing a fresh cartridge.
See also: single action, double action.
ACCIDENTAL DISCHARGE – An unexpected and undesirable discharge of a firearm caused by circumstances beyond the control of the participant(s) such as a mechanical failure or parts breakage. There are very, very few firearms related “accidents” and if the “4 Rules” are followed there will hopefully be no injury. Compare with Negligent Discharge.
ADJUSTABLE STOCK – The stock is the wooden, polymer, or metal handle of a long gun that extends from the trigger back to where the gun is braced against the shoulder. An adjustable stock is one that can be easily lengthened or shortened to fit shooters of different sizes.
ADJUSTABLE TRIGGER – A trigger that can be easily adjusted by the user. Adjustable triggers are common on specialized target-shooting firearms, but rare on self defense firearms.
AIRGUN – Not a firearm but a gun that uses compressed air or CO2 to propel a projectile. Examples: BB gun, pellet gun, CO2 gun.
AMBIDEXTEROUS SAFETY – A manual, external safety which can be easily reached with either hand. Usually one lever on each side of the firearm.
AMMO – Short for Ammunition
AMMUNITION – The “packaged” components that are needed in order to fire in a case or shell holding a primer, (which produces the spark) a charge of propellant (gunpowder) and a projectile (bullets, slug or pellets.) Sometimes called “fixed ammunition” to differentiate from the individual components placed separately in muzzleloaders. A single unit of ammunition in modern firearms is called a cartridge. The units of measure for quantity of ammunition is rounds. There are hundreds of sizes of ammunition, examples include .223 Remington, 9mm Luger, 30.06, .308 Winchester, .300 Winchester Magnum, and .50 Browning Machine Gun (BMG). The ammunition used must match the firearm.
ANTIQUE – By federal definition, a firearm manufactured prior to 1899 or a firearm for which ammunition is not generally available or a firearm incapable of firing fixed ammunition.
APERTURE SIGHT – An iron sight system of aligned markers used to assist in the aiming of a device such as a firearm, crossbow, or telescope that excludes the use of optics as in a scope. Also known as Peep Sights.
AR-15 – >is a widely owned semi-automatic rifle. The AR does not stand for “Assualt Rifle” as many believe, it was named after the manufacturer that first built it, Armalite.
ARMOR-PIERCING AMMUNITION – A type of ammunition designed to penetrate armor or armor-plated targets such as tanks, trucks, and other vehicles. An armor-piercing shell must withstand the shock of punching through armor plating. Shells designed for this purpose have a greatly strengthened case with a specially hardened and shaped nose, and a much smaller bursting charge.
ARSENAL – A government establishment where firearms and ammunition are stored, repaired, or manufactured. The term is misused by the media to mean more than one firearm or any quantity of ammunition, as in “they found an arsenal.”
ARTILLERY – Large bore diameter (nominally 3″ or greater) firearms designed to be operated by a crew of individuals. They are utilized to project explosive, armor defeating, incendiary, or nuclear projectiles over great distances. They are normally moved by vehicle because of their size and weight. “Cannon,” mortars, howitzers, and similar are considered artillery.
ASSAULT RIFLE – A military firearm which fires a reduced-power rifle round, and can shoot in both fully-automatic and semi-automatic modes.
ASSAULT WEAPON – A political term with no fixed definition, being defined differently by different jurisdictions. Because the actual definition is so fluid, laws written to regulate assault weapons often define the term by various cosmetic characteristics which do not affect a firearm’s power or function in any fundamental way. Despite public perception, assault weapons are not machine guns. They are semi-automatic firearms, not fully automatic firearms.
The term is distinct from the term assault rifle, which is a technical term with a specific meaning widely accepted both in law and within the military and firearms communities.
AUTOLOADER – A firearm that automatically loads the next cartridge to be fired into the chamber either upon the pull of the trigger in an open bolt design or upon the firing of the previous round in a close bolt design. Over time this term has been shortened to just “auto” and sometimes “automatic” thus creating confusion between a full-auto firearm and a semi-automatic firearm.
AUTOMATIC – A firearm designed to feed cartridges, fire them, eject their empty cases and repeat this cycle as long as the trigger is depressed and cartridges remain in the feed system. Examples: machine guns, submachine guns, selective-fire rifles, including true assault rifles. A fully automatic firearm is capable of sequentially firing two or more cartridges with a single pull of the trigger. A fully automatic firearm is also called a machine gun.
Automatic can also refer to a semi-automatic firearm.
BALL – Originally a spherical projectile, now generally a fully jacketed bullet of cylindrical profile capped with a round nose.
BALLISTICS – The science of cartridge discharge and the bullet’s flight. Internal ballistics deals with what happens inside of a firearm upon discharge. External ballistics is the study of a projectile’s flight, and terminal ballistics is the study of the impact of a projectile.
BALLISTIC FINGERPRINT – A fired case has marks upon it that it picked up from the extractor, ejector, and breechface of the gun when the shot went off. A bullet fired through a rifled barrel also has rifling marks unique to the barrel that launched it. A record of these marks, when stored in a central database, is called a ballistic fingerprint. Some states require this record to be made by law, so that individual guns can be located from bullets or casings found at the scene of a crime.
BARREL – The metal tube through which the bullet or shot travels. The barrel serves the purpose of providing direction and velocity to the bullet.
BATTERY – Most firearms do not have literal batteries. But a firearm is said to be in battery when the breech is fully closed and locked, ready to fire. When the breech is open or unlocked, the gun is out of battery and no attempt should be made to fire it. A semi-automatic is out of battery when the slide fails to come all the way forward again after the gun has fired, making it dangerous or impossible to fire the next round. This condition can be created by a misfeed, a dirty gun, weak springs, the shooter’s thumbs brushing against the slide, riding the slide, or any of several other causes.
BACKSTOP – Anything that will safely stop a bullet and prevent it from hitting anything else after the target is struck.
BACKSTRAP – A handgun term. The rearmost surface of the grip. The rear of two gripstraps on a handgun, which lies beneath the heel of the hand when gripping the gun.
BAYONET LUG – A mounting point on a small arm that allows a bayonet or other accessory to be attached.
BEAVERTAIL – A large piece of curved metal at the top of the grip which protects the user’s hand from getting bitten by the hammer. It is nearly always the top part of the grip safety commonly found on many 1911-style pistols,
BENCHREST (Shooting) – A shooting sport in which the competitors seek to place five or ten consecutive shots into the smallest possible group on a paper target at various ranges. All firing is done from an artificially supported shooting position. It is a severe test of the mechanical precision of both the small arm and its ammunition.
BERM – On an outdoor shooting range, a large pile of dirt that functions as a backstop.
BIATHLON – A shooting sport that combines both skiing and rifle shooting. It is the only shooting activity in the Winter Olympics. There is also a summer biathlon which involves running and shooting but it is not yet an Olympic event.
BIPOD – A two legged support for the front end of a rifle to stabilize the gun while shooting.
BIRDSHOT – A type of shotgun ammunition which uses very small pellets with individual projectiles of less than .24″ in diameter designed to be discharged in quantity from the shotgun. The size of the shot is given as a number or letter–with the larger number the smaller the shot size. It is so named because it is most often used for hunting birds. The finest size generally used is #9 which is approximately .08″ in diameter and the largest common size is #2 which is approximately .15″
BLACKPOWDER – The earliest type of firearms propellant that has generally been replaced by smokeless powder except for use in muzzleloaders and older breechloading guns that demand its lower pressure levels.
BLOWBACK – A semi-automatic firearm whose breechblock and barrel are not mechanically locked together when fired. In such case the breechblock immediately begins to separate from the barrel upon firing. Blowback is used in comparatively low powered weapons, in which inertia of the breechblock, and cartridge wall adhesion against the chamber, are sufficient enough to retard opening until breech gas pressures have fallen to a safe level.
BLANK CARTRIDGE – A round loaded with blackpowder or a special smokeless powder but lacking a projectile. Used mainly in starting races, theatrical productions, troop exercises and in training dogs.
BLUING – The chemical process of artificial oxidation (rusting) applied to gun parts so that the metal attains a dark blue or nearly black appearance.
BOAT TAIL – A type of projectile that has a tapered base (rear end) that reduces the drag from the air as it travels to its target.
BOLT – The mechanism of some firearms that holds the cartridge in place during the firing process. It must be moved out of the way to load and unload the gun; this action may be manually performed by the shooter pulling back on an exterior knob called the bolt handle and then sending it forward again, or the action may be performed by other moving parts within the firearm. When the user must move the bolt manually, the firearm is called a bolt-action firearm.
BOLT ACTION – A type of firearm, almost always a rifle, in which an empty shell casing is removed from the firing chamber by the turning and retraction of a metal cylinder shaped mechanism called a bolt. A new, unfired, cartridge is inserted and secured into the chamber by reversing the action of the bolt.
BORE – The hollow portion of a barrel through which the bullet travels during it’s acceleration phase.
BORE DIAMETER – The diameter of the inside of the barrel after boring, but before rifling.
BORE AXIS – An imaginary line which runs right down the center of the handgun’s barrel and out though the back end of the gun. A handgun may have a high bore axis, with the imaginary line running out into space well above the shooter’s hand. Or it may have a low bore axis, with the imaginary line running either straight through the shooter’s hand or just skimming the surface slightly above her hand. A high bore axis tends to create greater perceived recoil and more muzzle flip when firing the gun than does a low bore axis.
BOTTLENECKED – A type of cartridge whose bullet diameter is substantially less than the body diameter of the casing.
BRASS – A slang term for an empty shell casing. Most shell casings are made of the metal alloy known as brass.
BREAK – (Trigger Break) The point at which the trigger allows the hammer to fall, or releases the striker, so that the shot fires. The ideal trigger break is sudden and definite. “Like a glass rod” is the cliché term shooters use to describe the ideal crisp, clean break.
BREECH – That portion of the gun that contains the rear chamber portion of the barrel. The rearmost end of a barrel, closest to the shooter.
BEECH LOADING GUN – a firearm in which the cartridge or shell isinserted or loaded into a chamber to the rear portion of a barrel.
BREECH BLOCK – The part of the weapon that seals the rear of the chamber (the breech) while the gun is firing, preventing the rearward escape of gases.
BREECH FACE – That portion of the breech block which touches the cartridge when the breech is closed.
BREECH OPENING – The open rear of the barrel through which cartridges are inserted into the chamber.
BRICK – A box of ammunition roughly equal in size and weight to a brick. Most often used to describe a 500-round container of 22 Long Rifle ammunition.
BUCKSHOT – A type of shotgun ammunition that uses medium-sized to large-sized pellets of .24″ in diameter or greater, designed to be discharged in quantity from a shotgun. Generally the larger the pellets, the fewer of them there are in casing.
BULLET – The single metal projectile expelled from a gun. It is not the same as a cartridge, the cartridge is complete package, which includes the case, primer, powder, and bullet, which is called or a round. Bullets can be of many materials, shapes, weights and constructions such as solid lead, lead with a jacket of harder metal, round-nosed, flat-nosed, hollow-pointed, etc.
BULLET PROOF VEST – A popular but incorrect term forbullet resistant clothing.
BULLET TRAP – A type of backstop that catches the fired bullet and prevents it from exiting the area. Bullet traps are most commonly used on indoor ranges.
BULLPUP – A rifle configuration in which the action and magazine are located behind the trigger. This makes the overall length of the firearm shorter than it otherwise would be.
BUTT – The base of the grip on a handgun and the rearmost portion of the stock on a long gun that braces against the shoulder.
BULL BARREL – “Bull barrels” are barrels that are not tapered at all. These very heavy barrels, designed for extreme accuracy, are usually seen on target rifles.
CABLE LOCK – A cable with a padlock at the end. It is threaded through the action of the firearm.
CALIBER – The diameter of the bore of a firearm measured as a fraction of an inch. Although such a measurement may be frequently stated in millimeters. It is correctly expressed as “.40 caliber” (note the decimal point) or as “10 millimeter” (without “caliber” or the leading decimal point). Caliber numbers when used to identify the size of the bullet a gun will file are usually followed by words or letters to create the complete name of the cartridge. These letters often represent a brand name or an abbreviation for the name of the company that first introduced the round.
CAN – Slang term for a firearm sound suppressor.
CANNELURE – A groove or indention around the circumference of a bullet. Its purpose is to permit the cartridge casing to be crimped tightly against the bullet shank to hold it firmly to the casing. A groove or indention around the circumference of a bullet. Its purpose is to permit the cartridge casing to be crimped tightly against the bullet shank to hold it firmly to the casing.
CANT – Tilting the firearm slightly to one side, so the grip is no longer vertical in relation to the ground. Canting the firearm can make precision shooting more difficult, but may be necessary in some circumstances.
CARBINE – A rifle with a relatively short barrel. Any rifle or carbine with a barrel less than 16″ long must be registered with the Bureau of Alcohol, Tobacco and Firearms. Shotguns with barrels less than 18″ long fall into the same category. Commonly used today to indicate any rifle of short overall length.
CARTRIDGE – A single, complete round of ammunition which includes the case, primer, powder, and bullet
CASE, CASING – The envelope (container) of a cartridge. For rifles and handguns it is usually of brass or other metal; for shotguns it is usually of paper or plastic with a metal head and is more often called a “shell.”
CENTER-FIRE – A cartridge with its primer located in the center of the base of the case.
CENTER OF MASS (COM) For self-defensive shooters, COM represents the area of an attackers torso within which the most vital organs are likely to be disrupted by a gunshot. Shooting to COM is considered the most expedient way to stop an assailant from continuing threatening behavior.
CHAMBER – The rear part of the barrel that is formed to accept the cartridge to be fired. A revolver employs a multi-chambered rotating cylinder separated from the stationary barrel.
CHAMBER THROAT – This is the area in the barrel that is directly forward of the chamber, which tapers to the bore diameter.
CHARGER- A device typically made from stamped metal which holds a group of cartridges for easy and virtually simultaneous loading into the fixed magazine of a firearm.
CHOKE – A constriction at or near the muzzle of a shotgun barrel that affects shot dispersion.
CLAY PIGEON – Originally, live pigeons were used as targets, but they were gradually replaced with clay disks and ultimately banned. Later clay has been replaced with more suitable raw materials.
CLEARING – Unloading a gun and double checking that it is unloaded or fixing a malfunction so that the gun is ready to fire again.
CLICKS – A unit of adjustment for a sight.
CLIP – The controversial name commonly used to describe a magazine which is an ammunition storage and feeding device Magazines may be integral to the firearm (fixed) or removable (detachable). The magazine functions by moving the cartridges stored in the magazine into a position where they may be loaded into the chamber by the action of the firearm.
CLOSED BOLT FIRING (SYSTEM) – A type of firearm in which the action is closed, with a cartridge in the chamber prior to firing. When the trigger is pressed the cartridge is fired, and the action cycles loading another cartridge into chamber and when firing is stopped the bolt remains closed and the chamber remains loaded.
COCK – The term referring to the action of manually drawing the hammer back against its spring until it becomes latched against the sear, or sometimes the trigger itself, arming the hammer to be released by a subsequent pull of the trigger. Some external hammers, and all internal hammers, may be cocked simply by pulling the trigger
COCKED – A state of readiness of a firearm. The hammer (or similar mechanism if there is no hammer) only needs to be released by the trigger to cause the gun to fire.
COLD CLEAN BORE – The first shot from a rifle that has been cleaned, and not fired recently may go to a different point of impact, for the same point of aim than a rifle that has been fired recently. This first shot is referred to as a shot from a cold, clean, bore. See also fouling shot.
COLD RANGE – Pistol must be unloaded until it is your turn to shoot
COLLAPSIBLE STOCK – A stock on a long gun that can be shoved into itself to shorten it, either for storage or to make the gun fit shooters of different sizes.
COMPENSATOR – Also call a Muzzle Brake. A device attached to or made as part of a firearms barrel designed to reduce recoil or muzzle movement on firing. They generally increase muzzle blast. The may also, but not necessarily so, diminish muzzle flash.
CONCEALED – Hidden from view. A handgun is concealed when it is carried in such a manner that is unseen
CONTROLLED PAIR – Two shots fired in rapid succession. It is different from a double tap because in a controlled pair, the second shot will be fired after the shooter has obtained a second sight picture, whereas in a double tap both shots are fired based upon the initial sight picture alone.
COVER – Anything an intended victim hides behind that will probably stop a bullet.
COVER GARMENT – Any piece of clothing that covers the holstered gun. When the gun is worn on the belt, the most common types of cover garments are vests, sweaters, and jackets.
CO-WITNESS SIGHTING – is the use of any iron sight mounted onto a rifle that is fitted with an optical sight as a primary sighting system. They come in two basic configurations, fixed or flip-up. The idea is that if you align your red dot and your iron sights you have a backup aiming system on the gun/
CROSS-DOMINANT- This means a shooter who is right-handed but left-eyed, or left-handed and right-eyed.
CROSSHAIRS – The cross-shaped object seen in the center of a firearm scope. Its more-proper name is reticle.
CROWN – The area inside the bore nearest the muzzle. Damage to the crown can severely and adversely affect the firearm’s accuracy.
CYLINDER – A rotating cartridge holder in a revolver. The cartridges are held in the chambers and the cylinder turns, either to the left or to the right depending on the gun maker’s design, as the hammer is cocked.
CYLINDER DRUM – On a revolver, a spring activated device housed in the bottom of the frame beneath the cylinder that engages alignment notches in the cylinder. It stops the cylinder’s rotation and holds it in place each time a chamber in the cylinder is in alignment with the barrel.