A BB gun is a type of air gun designed to shoot metallic spherical projectiles called BBs, which are approximately the same size as BB-size lead birdshot used in shotguns. Modern BB guns usually have a smoothbore barrel with a 4.5 mm (0.177 in) caliber, and use steel balls that measure 4.3–4.4 mm (0.171–0.173 in) in diameter and 0.33–0.35 g (5.1–5.4 gr) in weight, usually zinc- or copper-plated for corrosion resistance. Some manufacturers still make the slightly larger traditional lead balls that weigh around 0.48–0.50 g (7.4–7.7 gr), which are generally intended for use in rifled barrels.
BB pistol with CO2 cartridges and BBs
Steel BBs with copper or zinc jackets
BB gun injury showing a 4.5 mm steel BB that penetrated the middle finger on the left hand
An air gun or airgun is a gun that uses energy from compressed air or other gases that are mechanically pressurized and then released to propel and accelerate projectiles, similar to the principle of the primitive blowgun. This is in contrast to a firearm, which shoots projectiles using energy generated via exothermic combustion (deflagration) of chemical propellants, most often black powder or smokeless powder.
A collection of spring-piston air rifles
Under Lever Spring Piston Air Rifles
Kunitomo air gun trigger mechanism
Variety of different types & models of spring piston & gas ram air guns