Did you mean Compressed Light Gas Gun (CLGG) or
Light Gas Gun (LGG)?A gas gun can be:A projectile-firing gun powered by compressed air: see
Air gunA
riot gun, especially when loaded with
CS gas grenades.A pneumatic cannon for projectile-firing test equipment such as a
birdstrike simulatorA gun that fires a stream of gas. This can be for these purposes among others:-The generate a loud noise as a
bird scarerPoisonous gas, for close-up silent assassinationFor propulsion in space: see Manned Maneuvering Unit#NASA "gas gun"
See more at Wikipedia.org...