BB (ammunition)

BB guns are a type of air gun designed to fire spherical metal projectiles similar to shot pellets of approximately the same size. Modern BB guns usually have a barrel with a bore caliber of 4.5 mm (0.177 in) and are available in many varieties. These guns usually use steel BB shots, plated either with zinc or copper to resist corrosion, and measure 4.3 to 4.4 mm (0.171 to 0.173 in) in diameter and 0.33 to 0.35 g (5.1 to 5.4 gr) in weight. Some manufacturers still make lead balls around 0.48 to 0.50 g (7.4 to 7.7 gr) in weight and slightly larger in diameter, which are generally intended for use in rifled barrels.

The term "BB gun" is often incorrectly used to describe a pellet gun, which fires non-spherical projectiles. Although in many cases a steel BB can be fired in a pellet gun, pellets usually cannot be fired in a gun specifically designed for BBs. Similarly, the term is also often used incorrectly to address airsoft guns, which shoot plastic balls that are larger but much less dense.

The term BB originated from the nomenclature of the size of steel shots used in a shotgun. Size "BB" shots were normally 0.180 inches (4.6 mm), but tended to vary considerably in size due to the loose tolerances in shotgun shells. The highest size shotgun pellet commonly used was named OO or double ought and was used for hunting deer and thus called buckshot, while the smaller BB-sized shot was typically used to shoot small/medium-sized birds and therefore was a birdshot.

Around 1900, Daisy Manufacturing Company (formerly Plymouth Air Rifle Company), one of the earliest makers of birdshot-caliber air rifles, changed their BB-size bore diameter to 0.175 inches (4.4 mm), and began to market precision-made lead shot specifically for their BB guns. They called these round shots, but the BB name was already well established, and most users continued calling their guns BB guns and the shot BB shot or just BBs.

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