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How Do Gas BB Guns Work?

Updated February 21, 2017

BB guns are smooth bore weapons that fire small round balls made of either plastic or metal, using compressed gas as the source of propulsion. The typical metal BB is about 4.5mm in diameter, while AirSoft BB guns fire plastic balls that are about 6mm. BB guns can have a variety of sources for this compressed gas.

BB Gun Basics

BB guns are smooth bore weapons that fire small round balls made of either plastic or metal, using compressed gas as the source of propulsion. The typical metal BB is about 4.5mm in diameter, while AirSoft BB guns fire plastic balls that are about 6mm. BB guns can have a variety of sources for this compressed gas.

Spring Pistons

Spring pistons can achieve a lot of power, with BBs reaching velocities approaching the speed of sound. They work by cranking a spring, which when released pushes a piston that compresses the gas charge for firing the gun. The strength needed to crank the piston is directly proportional to the power of the gas charge, so a powerful spring piston BB gun will require considerable brute force to crank. These cranks come in the form of a lever-action, slide-action, or sometimes even using the barrel as a lever. Each release of the piston requires the gun to be cranked back up again before shooting. These BB guns are invariably single-shot, although they may hold a considerable number of BBs. Most toy BB guns use a lever-action crank, and have very weak springs and low velocities.

Pneumatic Guns

These guns replace the piston with a canister of compressed gas. There is no cranked spring and piston. The typical BB gun of this type uses a powerlet, or canister filled with 12 grams of liquid carbon dioxide. These are the same cartridges used to power paintball pistols. Since the power source is a tank of pre-compressed gas, these guns are multi-shot. But they have two different sources of ammunition: their powerlet and their BBs.

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