Abstract: A gas operated firearm having means for initially storing energy from the gases released during discharge of a bullet is disclosed. The firearm includes a piston and cylinder arrangement which receives such gases, with the piston moving forwardly to compress a spring and operate a latch mechanism to maintain the spring in the compressed condition. The latch mechanism may be released by the operator when it is desired to reload the firearm, with reloading being accomplished by operation of an interengaging piston connecting rod and slide connecting rod.