US Patent 9915496 Light gas gun

An improved light gas gun launches a projectile in a light gas atmosphere as it travels through a frictionless barrel to achieve high muzzle velocities, decreased acoustic signatures, and increased ranges. The light gas atmosphere is introduced by a purge valve prior to firing or by a muzzle valve that holds a positive light gas pressure on the barrel and breech. The muzzle valve also routes the majority of propellant gases through a suppression canister, reducing the light gas gun's acoustic signature. The frictionless barrel uses light gas propellant routed through gas bearings to keep the projectile centered in the barrel and preclude the projectile from contacting the barrel walls, eliminating barrel wear.