Dictionary of Standard Firearms Terms
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+P – The SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) designation for ammunition loaded to a higher pressure. +P is usually marked on the base of the cartridge case and should only be used in firearms specially designed for higher pressure ammo as recommended by the firearm’s manufacturer or user manual.
+P+ – Ammunition loaded to even higher pressures than +P ammunition. This term is not an official SAAMI designation and this type of ammo should be used responsibly. You should always consult the firearm manufacturer or owner’s manual before using any overpressure ammunition.
Action – A general term applied to the operating mechanism on a firearm. Some examples of action types are bolt-action, lever-action, semi-automatic and pump-action. This term is also used to describe the mechanical area of a firearm that may include the moving parts.
AR – A term most commonly used to refer to the AR-15 rifle. Sometimes incorrectly understood to mean “Assault Rifle,” when, in fact, it means “Armalite Rifle.”
Assault Rifle –An automatic rifle designed for combat and general issue to militaries. Normally chambered in an intermediate round and fed from a large box magazine. Assault rifles are highly regulated by the federal government.
Assault Weapon – A term created by gun-control advocates to incorrectly describe modern sporting rifles with features resembling actual assault rifles. The term was coined by The Brady Campaign to Prevent Gun Violence and confuses the distinction between sporting rifles and actual assault rifles.
Automatic –A firearm that chambers, fires and ejects more than one cartridge with one pull of the trigger. Automatic firearms are highly regulated by the federal government and sometimes referred to as “select fire” weapons.
Belted Magnum –A case developed by Holland & Holland featuring a prominent belt forward of the base. The cartridge headspaces off of the thick rim instead of off the rim, shoulder or case mouth like other cartridges.
Berdan Primer – Cartridge primer invented in 1866 by Hiram Berdan. This primer system uses multiple small flash holes that are off-center. They are very unpopular with reloaders because they're difficult to remove from cartridges, unlike Boxer primers, which have a central flash hole. Berdan primers are generally used in non-US military surplus ammo and are almost never used in new production brass cartridges.
Birdshot – Small metal balls, or shot, used when hunting birds or small game with a shotgun. Birdshot can also be used for shooting sporting clays or trap. Generally made from lead, steel and other lead-free materials it varies in size from the relatively large BB size all the way down to the very small #12.
Black Powder –Originally called gunpowder, now called black powder to distinguish it from the more modern smokeless powder. Often abbreviated BP, it's a mixture of potassium nitrate (saltpeter), sulfur and charcoal. Less powerful than smokeless powder, it produces more fouling (deposits) and a large amount of smoke when ignited. Black powder is commonly used in muzzleloaders and can be ignited by a spark, static electricity, heat or a sharp blow.
Bolt Action – A firearm action that resembles a door bolt. Cycling the bolt will eject a spent cartridge, load a fresh one and cock the rifle. There are two types of bolt action, controlled feed and push feed. Bolt action is considered to be one of the most reliable firearm actions.
Bore – The hollow part of the barrel. Also used to describe some shotgun shell sizes.
Breech – The portion of the barrel behind the bore. It depends on the model of gun to determine the breech area. It can contain the chamber or be a simple reference to the back of the barrel.
Caliber – The term used to identify the diameter of a projectile of the barrel, normally measures in inches or millimeters.
Carbine – A short rifle that is a handy, easily maneuverable size. A carbine is normally a shortened version of an existing rifle. It can also be used to identify the gas system length on the AR-15 rifle.
Case – Sometimes called brass, empties, shells, reloading brass, spent cases or brass cases. The case is designed to contain the powder charge and the primer. Cases can be made of brass, aluminum, steel, polymer or a combination of those materials.
Centerfire – A cartridge with a centrally located primer of any type. This term can also be used to describe any firearm that uses a centerfire cartridge.
Chamber – The portion of the barrel the cartridge is inserted into prior to being fired. In revolvers, the chamber is found in the cylinder.
Clip – Used to refer to stripper clips, metal strips containing cartridges to be fed into a magazine more easily. This term is sometimes used improperly to describe a removable magazine.
Cock – Used to describe the arm assembly that holds the flint on a flintlock rifle. Also can be used as a verb meaning to make ready to fire; for example, “to cock the gun.”
Compensator – A muzzle device with open ports on the top of the device to redirect gasses in an effort to combat muzzle rise.
Crown – The finished end of a barrel cut to a precise angle ensuring the projectile exits the barrel evenly. Crowns are purported to affect accuracy; however, some testing has revealed it has little effect.
Cylinder – The revolving portion of a revolver containing the chamber. The cylinder rotates to index each cartridge with the chamber to be fired.
Decocker – A lever, switch or button that safely releases the hammer’s spring to remove the firearm from a cocked state. The decocker will lower the hammer on most firearms equipped with this feature.
DoubleAction – A fire control group that cocks the firearm then fires the gun by releasing the sear with one pull of the trigger. Also used in conjunction with a single action system in a DA/SA trigger.
Ejector – The mechanism that kicks the spent case or hull free from the chamber.
Elevation – The adjustment that raises or lowers the point of impact. This can also be accomplished by adjusting the sights as well as by holding your aim over or under the target.
Extractor – The mechanism that pulls a case free from the chamber. Normally accomplished by a hook type fixture attached to the breech face. Except in the case of revolvers that have a star shaped extractor attached to the cylinder and break-action long guns that have an extractor as a part of the action.
Firing Pin – The needle or nail-like device that strikes the primer causing the priming compound to ignite which, in turn, ignites the powder propelling the projectile out of the barrel.
FlashHider – Shields the shooter's eyes from the powder flash at the muzzle so he is not blinded by the sudden bright light when firing. Most useful at night to help the shooter preserve his night vision.
Flintlock – A type of action found on muzzleloading black powder firearms. The flint rides in the cock and is struck against the frizzen (a spoon-shaped piece of steel) resulting in a spark that ignites the priming charge in the pan. The flame then shoots through the flash hole in the breech to ignite the main charge.
Forcing Cone – A truncated cone found in the barrels of revolvers and shotguns to center the projectile in the bore.
Forend – The portion of the stock located forward of the action. Commonly referred to as rails on modern rifles featuring accessory rails.
Fouling – The buildup of carbon, lead, wax, copper and anything else that accumulates in the bore as a result of the firing process. Accumulation of fouling can decrease accuracy and over time can build up making the bore too small for a bullet to pass through.
FPS – The abbreviation for Feet Per Second. This is the common unit of measurement when referring to projectile speed or muzzle velocity.
Frame –The part of the firearm also known as the receiver which houses the majority of the action.
FullAutomatic – A term refering to select fire machine guns. Semi-automatic firearms are not considered full-automatic because a full-automatic firearm will continue to fire as long as the trigger is held. As opposed to a semi-automatic firearm which will continue to fire with each trigger pull. This term is sometimes shortened to full-auto.
Gas Operated – A firearm action that gathers gas from either a port drilled in the barrel or a collar that affixes to the muzzle to collect gasses as they exit the barrel. The expanding gasses are then used to operate the action via direct impingement or an operating rod.
Gauge – A unit of measurement designating the caliber of a shotgun and shotgun ammunition.
Grain – The unit of measure for ammunition components. One pound will equal 7,000 grains, one grain is equal to .0648 grams.
Groove – A term describing the recessed part of the rifling. The lands stick up to define the borders of the grooves.
Hammer – A spring loaded arm released when pulling the trigger to impact the firing pin.
Headspace –The measurement of the chamber with the breech closed. Proper headspace is necessary for the firearms to function properly. Too little headspace can result in an out of battery detonation, too much and the case can stretch or even burst.
Iron Sights – A term referring to simple non-optical sights. They are called iron sights because they are constructed primarily of metal.
Land – The raised portion of the rifling found in the bore that spins the bullet to stabilize its flight. The lands form the borders of the grooves.
Length of Pull – The measurement from the face of the trigger to the end of the buttstock, recoil pad or buttpad. This measurement is used to fit a long gun to a shooter.
Lever Action – The term describing a firearm action operated by the user using a manually cycled lever. This is not a semi-automatic action.
Lock – A term normally used to describe the fire control group found on muzzleloaders. Common types include matchlock, wheellock, flintlock and percussion locks. In modern firearms, the lock is referred to as the action or fire control group.
Machine Gun – A firearm that fires more than one cartridge with a single pull of the trigger. Highly regulated, normally restricted to law enforcement or the military with some exceptions.
Magnum – A designation indicating a cartridge is a more powerful loading than its smaller sibling, e.g. .44 Special to .44 Magnum.
Misfire – Used to describe a dud or failure to ignite when the primer is struck.
M.O.A. – The acronym for Minute Of Angle, an angular measurement used when measuring the accuracy of a rifle. It is also used as a unit of measurement when shooting long distance. MOA is roughly 1” per 100 yards. This can also be used to describe a red dot’s reticle size, e.g. 4 MOA dot = 4” coverage of the target at 100 yards.
Moly – The shortened term for molybdenum disulfide, a slick compound used to coat some ammunition to increase velocity and decrease leading of the bore.
Muzzle – The end of the barrel the projectile exits from.
Muzzleloader – A firearm loaded from the muzzle end by pushing the powder, patch and projectile with a ram rod.
Muzzle Rise – The tendency of firearms or the muzzle end of the barrel to rise up after firing. Also known as muzzle flip or muzzle climb. Compensators help to minimize muzzle rise.
Muzzle Velocity – The speed of the projectile as it exits the muzzle. Normally measured in feet per second (FPS).
Percussion – Can refer to a type of firearm lock or the act of detonating a percussion cap.
Percussion Cap – A small, thin metal cap containing an impact sensitive compound. When struck the compound explodes, igniting the main powder charge.
Percussion Lock – A firearm action that uses percussion caps to ignite the main charge.
Pistol – Any firearm designed to be fired while being held in one hand. Also called a handgun.
Point of Aim – The point where the sights indicate the bullet will impact.
Primer – The component of the cartridge that when struck ignites the main charge, sending the projectile down the bore. Primers come in various sizes and types.
Proofmark – An acceptance mark applied to a firearm after successfully firing one or more high-pressure loads.
Pump Action – A firearm action system using a pumping action of the forearm to eject the spent brass or hull and load a new cartridge into the chamber.
Receiver – This part of the gun is also known as the frame, it houses the majority of the action. Often the serialized part of the firearm and is considered a firearm in itself in the eyes of the law.
Revolver – A handgun with a revolving cylinder that houses several chambers. When cocking the gun it will advance the cylinder to the next chamber making a new cartridge available to be fired.
Rifling – Grooves that run in a spiral pattern on the inside of the bore in order to spin the projectile and stabilize it. Made up of alternating lands and grooves.
Rimfire Cartridge – A type of ammunition with the primer located in the rim of the case base. When the firing pin strikes the rim, it is crushed and ignites the primer in the rim.
Safety – A mechanical component preventing the gun from being fired by interfering with the fire control group’s action.
Sear – A catch in the firearm’s lock preventing the hammer from firing until the trigger is pulled.
Semi Automatic – Sometimes shortened to semi-auto, also referred to as a self-loader at times. This action will automatically eject a spent casing and load a fresh round into the chamber when the gun is fired using the energy of the fired cartridge. It will fire only one cartridge with each pull of the trigger.
Short Barreled Rifle (SBR) – A rifle with an overall length of less than 26” or a barrel length of less than 16” from the breech face. Federally regulated by the ATF and requires registration.
Short Barrel Shotgun (SBS) – A shotgun with an overall length of less than 26” or a barrel length of less than 18” from the breech face. Federally regulated by the ATF and requires registration.
Shot – Round balls (usually made of metal) used in shotgun shells. The balls vary in diameter but are uniform within one shotgun shell. They are given numbers or letters to designate their size. The larger shot has lower numbers (such as 4 and 5) and the smaller shot has higher numbers (such as 8 and 9).
Shotgun – A long gun that normally has a smooth bore that fires shot or slugs. Also known as a scattergun.
Shotshell – A cartridge used in a shotgun.
Side by Side – A term that refers to a gun with two barrels side by side. Sometimes abbreviated as S/S or SxS. This is normally a shotgun.
Sights – A device giving the shooter a point of reference when pointing a firearm at a target. Most firearms will have some sort of sighting system attached.
Single Action – A fire control group requiring the shooter to manually cock the hammer in order to fire. Unlike the double action, it will not cock the hammer as a process of the trigger pull.
Slug – A round projectile, larger than buckshot, used for short-range shooting. Also, a slang term for a bullet.
Smokeless Powder – The replacement for black powder. It was developed to burn at a safer rate while still being more potent than the volatile black powder. While not truly smokeless, it produces much less smoke than traditional black powder.
Speedloader – A device that eases or speeds up reloading a revolver or magazine. A revolver speed loader can load the entire cylinder in the time it takes to load one cartridge. The magazine speedloader, on the other hand, will help the user depress the cartridge into the magazine, saving time and their thumbs from the sharp feed lips.
Submachine Gun – A magazine-fed, fully automatic rifle designed to fire pistol cartridges. Highly regulated, normally restricted to law enforcement or the military with some exceptions.
Suppressor – A muzzle mounted device that functions as a muffler for gunshots. Federally regulated by the ATF and requires registration. Sometimes called a silencer.
Trajectory – The path the projectile takes from the moment it leaves the bore all the way to the target or point of impact.
Trigger – The mechanical interface that releases the sear to fire the gun.
Trigger Pull – The amount of force required to release the sear. Normally measured in pounds and ounces.
Twist Rate – The distance required for a barrel's rifling to turn one revolution. For example, 1:7 would indicate the rifling will make one full revolution in 7 inches. For more information on twist rate read our article What is Rifle Twist.
Windage – The adjustment that moves the point of impact left or right. This can also be accomplished by adjusting the sight or by holding your aim to the left or right of the target.