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...http://www.google.de/patents/US7337774?utm_source=gb-gplus-sharePatent US7337774 - Projectile firing device using liquified gas propellant
