Rifle (1) comprises barrel (2) and loading means (15) for introducing a projectile from magazine (7) into breech (4). The projectile is propelled by a compressed gas propellant initially stored as a liquid in canister (10). The liquid is heated to a super critical state in chamber (8) by heating element (12) to induce a phase change such that the liquid becomes a highly dense gas. The phase change from liquid to gas provides the energy required to expel the projectile at high velocity from rifle (1), regardless of the ambient temperature. The propellant is preferably CO.sub.2 which is heated to 31.06.degree. C. Rifle (1) produces minimal noise and no heat signature, making it suitable for military and stealth purposes. A pistol and launchers for grenades or mortar bombs are also disclosed. Another version can launch low earth orbit satellites or payloads.