+P                          Designates that the ammunition is loaded to a higher pressure. This is usually marked on the cartridge case. Use this ammo only in firearms specially designed for these higher pressures as recommended by the gun's manufacturer.

+P+                         Ammunition loaded to even higher pressure than +P. Again, use only in guns specially designed for this load. Typically used in defense situations and not for target shooting or general plinking.

ACP                      Automatic Colt Pistol

Action                      The mechanism that operates the chambering of a cartridge gun, e.g., bolt-action, lever-action and pump-action. Also used to describe the mechanical area of a gun that includes the bolt, chamber and ejection port.

Assault weapon           Term created by gun control advocates to demonize firearms.

Assault rifle              A combat rifle developed by the Germans during WWII (called Sturmgewehr), these rifles were made principally by Walther and Haenel. They offered mid-range power for troops requiring a compact rifle.

Automatic                An action that chambers, fires and ejects each cartridge in succession with one pull of the trigger. As long as the trigger is held down, the gun continues to fire until all ammo has been expended.

Belted magnum          A cartridge that has a prominent belt forward of the base. The headspace is on the belt rather than the rim or shoulder of the cartridge. Belted magnum cartridges are usually higher power.

Berdan primer          Cartridge ignition method invented in 1866 by Hiram Berdan, a Civil War-era ordnance officer, inventor and Sharpshooter. This primer system uses 2 or 3 smaller flash holes that are off-center. They are unpopular with reloaders because they're difficult to remove from cartridges, unlike Boxer primers, which have a central flash hole. Berdan-primed ammo is more popular outside the US and is generally used in non-US military surplus ammo.

Birdshot                  Ammo that is a small metal ball. Used for hunting birds or small game. Generally made of lead and varies from BB (larger) to #12 (smaller) shot sizes.

Black powder            Originally called gunpowder, it's 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. Used widely in sporting guns and blasting. Can be ignited by a spark, static electricity, heat or a sharp blow.

Bolt-action               An action that resembles a common door bolt (hence, the name). Cycling the bolt ejects a spent cartridge, loads a fresh one (if available) and cocks the rifle.

Bore                       The inside of the barrel.

Boxer primer            A primer invented in 1867 by British Colonel Edward Boxer. It's easier to remove from a spent cartridge, making it a favorite of reloaders and American ammunition manufacturers.

Breech                    The rear of the barrel. It depends on the model of gun to determine the breech area. It can contain the chamber, be a simple reference to the back of the barrel or just be the action behind the barrel.

Buttstock                 The rear most part of a rifle's stock. It rests against the shooter's shoulder.

Caliber                    The diameter of a projectile or barrel measured in inches or millimeters.

Carbine                   A short rifle. There is no established length for a carbine.

Cartridge                 A loaded round of ammunition that includes the case, primer, powder charge and projectile.

Case                       A component of ammunition that contains the primer, powder charge and projectile.

Centerfire                Any cartridge that has a Berdan or Boxer priming system. Also refers to any firearm that uses centerfire cartridges, e.g., centerfire rifle.

Chamber                 A cavity in a firearm that accepts a cartridge. It may be found in the barrel or, in the case of revolvers, in the separate cylinder.

Choke                     A reduction of the diameter at the end of a shotgun barrel that changes the pattern/spread of shot as it leaves the gun. Some shotguns have screw-on, interchangeable chokes. Some target rifle barrels are constricted at the end, and that is also called a choke - it stabilizes the bullet before it exits the muzzle.

Clip                       A device that contains cartridges outside a firearm and feeds them more readily.

Cock                      A mechanical portion of a flintlock or other old firearm lock. Also, a verb meaning to make a gun ready to fire, i.e., to cock.

Crown                    A cut applied to the end of a barrel to ensure that the projectile's base exits evenly from the rifling. Different types of crowns result in different levels of accuracy.

Cylinder                 The revolving section of a firearm that holds cartridges. It rotates to index each cartridge with the chamber so it can be fired.

Decocker                 A lever that safely releases the hammer's spring tension and makes a gun uncocked.

Double-action           A function that lets the trigger cock the hammer and release the sear, which results in firing the gun.

Ejector                   A mechanism that kicks out a spent case from the chamber.

Elevation                An adjustment mechanism that lowers or raises the sight to change the point of aim, which then changes the point of impact.

Extractor                A mechanism that pulls a spent case from the chamber.

Firing pin                A device that strikes the primer and causes ignition, which then travels to the main powder charge and ignites it.

Flash-hider              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 firing mechanism in muzzleloading firearms. Flint is used to strike a frizzen (piece of steel), which results in a spark that ignites the priming charge (a small pan of powder). The priming charge shoots flame through a small hole in the breech to ignite the main charge.

Forend                   The portion of the stock located forward of the action.

Fouling                   Build up of bore residues such as powder, copper, lead and wax. These deposits accumulate in the bore because of high heat during firing. Fouling accumulation may cause a decrease in accuracy.

F.P.S.                     Feet per second. The unit of measurement for the rate of speed of a projectile.

Frame                    Also known as the receiver, this is the part of a gun that houses the action.

Full-automatic          A slang term for an automatic action.

Gas-operated             A semi-automatic action that bleeds gasses from a fired cartridge. When the projectile passes the gas port (a hole) in the barrel, the gasses are vented into a chamber and cycle the action for the next shot.

Gauge                     Designates the caliber of a shotgun and shotgun ammunition.

Grain                      A unit of weight for bullets and balls that is derived from ancient agriculture. It is equal to the average of the grains taken from the middle of ears of wheat. A pound is 7,000 grains. One grain is equal to .0648 grams.

Groove                    The bore diameter of a rifled barrel. The lands (the portion that sticks up) define the boundaries of the grooves.

Hammer                  Part of a gun that strikes either the firing pin or the primer.

Headspace                The tolerance above the dimensions of the cartridge that is necessary for the gun to function properly. Too little headspace can result in difficult chambering. Too much headspace can cause the cartridge case to stretch and even burst.

Iron sights                Slang for non-optical sights found on a firearm.

Land                       A raised ridge in the bore of a rifled barrel that engraves the bullet and imparts a spin. The lands of a barrel define the bore-sized grooves.

Length of pull            The distance in a long gun from the trigger to the end of the buttstock, buttpad or recoil pad. Measured in inches, it varies from gun to gun and from manufacturer to manufacturer.

Lever-action              A mechanism that operates the bolt of the rifle. It performs the same functions as a bolt in a bolt-action, but it is smoother.

Lock                       The firing mechanism of a gun (usually a muzzleloader). Common types of locks include matchlock, wheelock, flintlock and percussion lock. Today's actions are also called locks.

Machine gun              A gun that fires multiple rounds with one pull of the trigger.

Magazine                  A removable unit that holds cartridges until they are fed into the chamber.

Magnum                   A designation for increased cartridge velocity and energy due to higher levels of powder, e.g., .38 Special to .357 Magnum and .44 Special to .44 Magnum.

Misfire                    A condition caused by ignition failure. Also called a "dud."

M.O.A.                     Minute of angle. Describes the level of accuracy of a gun. If a gun shoots a 1" group at 100 yds. and a 2" group at 200 yds., it shoots 1 M.O.A. It also describes the width of a scope reticle. For instance, if a scope's reticle or dot is 4 M.O.A., it covers 4 inches at 100 yds.

Moly                       Molybdenum disulfide. A very slick compound that is used in many places in firearms. Some ammunition is coated with moly. May increase velocity and accuracy.

Muzzle                     The end of the barrel.

Muzzlebrake              A device that attaches to the muzzle. Has vents or ports on the side or top to direct gasses up and to the side to reduce felt recoil and muzzle rise.

Muzzleloader             A firearm that is loaded by ramming (pushing) the projectile into the gun from the muzzle and down the barrel.

Muzzle velocity          The speed of a projectile as it exits the muzzle. The unit of measure is feet per second (f.p.s.).

Over-and-under         A type of long gun having 2 barrels, with one stacked on top of the other. Can be a shotgun or centerfire rifle or a combination of these two. Often designated O/U.

Percussion               The act of detonating a percussion cap in a firearm. Also designates a type of firearm lock.

Percussion cap           A thin metal cap containing an explosive substance, such as fulminate of mercury, that explodes when struck.

Percussion lock          A lock uses a percussion cap to ignite the gunpowder.

Pistol                      A firearm designed to be held and fired with one hand. Also called a handgun.

Point of aim              Where the sight of gun indicates the projectile is supposed to land.

Point of impact          Where a fired projectile actually lands.

Primer                    A cap or tube with a small amount of explosive. Used to ignite the main charge of a cartridge.

Proofmark                An acceptance mark given to a firearm that has successfully passed a test by firing one or more high-pressure loads.

Pump-action              A cocking mechanism that uses a back stroke of the gun's forearm to eject a spent cartridge and a forward stroke to automatically chamber a new cartridge.

Receiver                   Also known as the frame, it houses the action of a gun.

Revolver                   A gun with a cylindrical magazine that holds cartridges or gunpowder and projectiles. Operting the gun causes the cylinder to rotate, which puts a fresh cartridge or load in line with the barrel.

Rifling                     Grooves alternating with lands inside the barrel of a gun. See "twist rate" for more information.

Rimfire cartridge        Ammunition that has its primer charge in the rim of the base. When the firing pin strikes the rim, it detonates the priming charge, which ignites the main charge of gunpowder. Firearms using this type of cartridge are called rimfires.

Safety                      A device that prevents a gun from firing.

Sear                        A catch in a gun's lock that keeps the hammer or firing pin cocked.

Semi-automatic          Usually shortened to semi-auto and sometimes called a self-loader, this type of action automatically ejects a spent cartridge and loads the next one through the energy of the previously fired cartridge. It fires one cartridge with each pull of the trigger.

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. Larger shot has lower numbers (such as 4 and 5), and smaller shot has higher numbers (such as 8 and 9).

Shotgun                    A gun without a rifled barrel (also called a smoothbore) that fires shot or slugs over a shorter range than a rifle. Also known as a scattergun.

Shotshell                  A cartridge used in a shotgun.

Side-by-side              A slang term for a double-barreled gun, most often a shotgun.

Sights                     A means of reference that guides the shooter when directing the firearm. Modern firearms usually have attached sights.

Single-action            A trigger mechanism that performs just one action, which is releasing the hammer after it has been cocked. This differs from double-action, where pulling the trigger cocks the gun and fires it.

Slug                       A round projectile larger than buckshot and used for short-range shooting. Also, a slang term for a bullet.

Smokeless powder     The successor to black powder. It was developed to be safer and more potent, plus it does not produce as much smoke as black powder.

Speedloader             A device that eases or speeds up the process of reloading a revolver. It can load an entire cylinder in the same period of time that it takes to load one cartridge.

Submachine gun        A lightweight automatic gun that shoots pistol ammunition.

Trajectory               The path of the projectile from the moment it leaves the gun until it hits a target.

Trigger                  The mechanism that fires a gun.

Trigger pull            The amount of force that causes the sear to release.

Twist rate               The distance (in inches) required for a barrel's rifling to turn one revolution. For instance, 1:9 means the rifling makes one revolution in 9 inches.

Wadcutter               Cylinder-shaped bullet with flat ends. Designed for target shooting because it makes clearly defined round holes that are easier to score.

Windage                  A sight adjustment that moves the point of impact either right or left.

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