Firearm Glossary

ballistic coefficient or BC: a measure of projectiles ability to overcome air resistance in flight. It is inversely proportional to the deceleration—a high number indicates a low deceleration. BC is a function of mass, diameter, and drag coefficient. In bullets, it refers to the amount that drop over distance and wind drift affects the bullet.

barrel: A tube, usually metal, through which a controlled explosion or rapid expansion of gases are released to propel a projectile out of the end at high velocity.

black powder also called gunpowder: a mixture of sulfur, charcoal, and potassium nitrate. It burns rapidly, producing a volume of hot gas made up of carbon dioxide, water, and nitrogen, and a solid residue of potassium sulfide.Because of its burning properties and the amount of heat and gas volume that it generates, gunpowder has been widely used as a propellant in firearms and as a pyrotechnic composition in fireworks. Modern firearms do not use the traditional black powder described here, but instead use smokeless powder.

black-powder substitute: A firearm propellant that is designed to reproduce the burning rate and propellant properties of black powder (making it safe for use in black-powder firearms), while providing advantages in one or more areas such as reduced smoke, reduced corrosion, reduced cost, or decreased sensitivity to unintentional ignition.

blank: A type of cartridge for a firearm that contains gunpowder but no bullet or shot. When fired, the blank makes a flash and an explosive sound (report). Blanks are often used for simulation (such as in historical reenactments, theatre and movie special effects), training, and for signaling (see starting pistol). Blank cartridges differ from dummy cartridges, which are used for training or function testing firearms; these contain no primer or gunpowder, and are inert.

blowback: A system of operation for self-loading firearms that obtains power from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the powder charge

bluing or blueing: A passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. True gun bluing is an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite (Fe3O4), the black oxide of iron, which occupies the same volume as metallic iron. Bluing is most commonly used by gun manufacturers, gunsmiths and gun owners to improve the cosmetic appearance of, and provide a measure of corrosion resistance to, their firearms.

bolt action: A type of firearm action in which the firearm's bolt is operated manually by the opening and closing of the breech (barrel) with a small handle. As the handle is operated, the bolt is unlocked, the breech is opened, the spent shell casing is withdrawn and ejected, the firing pin is cocked, and finally a new round/shell (if available) is placed into the breech and the bolt closed.

bore snake: A tool used to clean the barrel of a gun.

boresight: Crude adjustments made to an optical firearm sight, or iron sights, to align the firearm barrel and sights. This method is usually used to pre-align the sights, which makes zeroing (zero drop at XX distance) much faster.

brass: The empty cartridge case.

break-action: A firearm whose barrels are hinged, and rotate perpendicular to the bore axis to expose the breech and allow loading and unloading of ammunition.

buffer: component that reduces the velocity of recoiling parts (such as the bolt).

burst mode: a firing mode enabling the shooter to fire a predetermined number of rounds with a single pull of the trigger.