Glossary of Firearms Terms - B

B

• back bore, backbored barrel: A shotgun barrel whose internal diameter is greater than nominal for the gauge, but less than the SAAMI maximum. Done in an attempt to reduce felt recoil, improve patterning, or change the balance of the shotgun.

• bandolier or bandoleer: A pocketed belt for holding ammunition and cartridges. It was usually slung over the chest. Bandoliers are now rare because most military arms use magazines which are not well-suited to being stored in such a manner. They are, however, still commonly used with shotguns, as individual 12 gauge shells can easily be stored in traditionally designed bandoliers.

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

• 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 will affect the bullet.

• bayonet lug: An attachment point for a bayonet.

• belt: ammunition belt is a device used to retain and feed cartridges into a firearm.

• belted magnum or belt: Any caliber cartridge, generally rifles, using a shell casing with a pronounced "belt" around its base that continues 2-4mm past the extractor groove. This design originated with the British gunmaker Holland & Holland for the purpose of headspace certain of their more powerful cartridges. Especially the non-shouldered (non-"bottlenecked") magnum rifle cartridges could be pushed too far into the chamber and thus cause catastrophic failure of the gun when fired with excessive headspace; the addition of the belt to the casing prevented this over-insertion.

• bipod: A support device that is similar to a tripod or monopod, but with two legs. On firearms, bipods are commonly used on rifles to provide a forward rest and reduce motion. The bipod permits the operator to rest the weapon on the ground, a low wall, or other object, reducing operator fatigue and permitting increased accuracy.

• 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 weapon'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.

• bolt thrust or breech pressure: The amount of rearward force exerted by the propellant gases on the bolt or breech of a firearm action or breech when a projectile is fired. The applied force has both magnitude and direction, making it a vector quantity.

• 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.

• breech pressure or Bolt thrust: The amount of rearward force exerted by the propellant gases on the bolt or breech of a firearm action or breech when a projectile is fired. The applied force has both magnitude and direction, making it a vector quantity.

• bullpup: a firearm configurations in which both the action and magazine are located behind the trigger.

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

• button rifling: Rifling that is formed by pulling a die made with reverse image of the rifling (the 'button') down the pre-drilled bore of a firearm barrel. See also cut rifling and hammer forging.