Patent ID: 7954413

Claim:
In a two-stage light gas gun comprised of a pump tube containing both a gas and a pump piston for compressing said gas, said pump tube connected to a launch tube, said launch tube containing a projectile, with a valve preventing the flow of said gas from said pump tube into said launch tube until said pump piston has sufficiently compressed said gas, wherein the improvement consists of: a) an expansion piston contained within an expansion tube, said expansion piston constrained to move longitudinally within said expansion tube, b) a piston rod rigidly connected to said expansion piston at one end and said pump piston at the opposite end, and c) a propellant gas, whereby pressure of said propellant gas causes said expansion piston to move longitudinally within said expansion tube transmitting force through said piston rod to said pump piston causing said pump piston to move longitudinally within said pump tube and compressing said gas to a pressure sufficient to open said valve and pass from said pump tube into said launch tube expelling said projectile from said launch tube, the piston rod is longitudinally coaxially aligned with a central axis of the launch tube during the entirety of the operation of the two-stage light gas gun, wherein a battery with associated spark plug acts to ignite said propellant gas to propel said expansion piston.