Pneumatic weapon

A pneumatic weapon is a weapon that fires a projectile by means of air pressure, similar in principle to the operation of pneumatic tube delivery systems. The term comes from a Greek word for "wind" or "breath" (πνεῦμα).

In theory, pneumatic weapons have certain advantages over traditional firearms:

In practice, pneumatic weapons are not as well-developed as traditional firearms and have a number of practical deficiencies:

The low projectile speed requirement of a toy weapon greatly reduces the amount of air pressure needed; combined with the importance of safety in the toy industry, this has led to widespread adoption of pneumatic firing mechanisms in toy weapons, where a propellant reaction is not appropriate (although other technologies, such as rubber bands, can be used).

The toy industry has produced a number of pneumatic toy weapons, which fire small, lightweight (often plastic and frequently hollow) projectiles at relatively low speeds. Airsoft and paintball guns are a popular toy that operates this way; when used with adequate safety equipment (eye protection at a minimum) these may be used in games involving shooting at other players.

BB guns and other low powered air guns, while often marketed towards the youth market, are not toys; the steel and lead projectiles they fire can readily penetrate the skin, and are capable of producing lethal wounds. While a lethal wound is unlikely due to their low power, air guns and BB guns should be used with the same precautions as firearms; eye protection for the shooter, a safe range, and an adequate backstop.

...
Wikipedia