Gas operated movable mass for ballistic model

Claim 1

A GUN FIRED PROJECTILE COMPRISING A HOLLOW CYLINDRICAL BODY HAVING A FORWARD WALL AND A REAR WALL AT THE END PORTIONS THEREOF RESPECTIVELY, A RELATIVELY HEAVY SLIDEABLE INERTIAL PLUG MOVABLE FROM A REARWARD POSITION IN ENGAGEMENT WITH SAID REAR WALL TO A FORWARD POSITION IN ENGAGEMEMT WITH SAID FORWARD WALL WITHIN SAID BODY, SAID PLUG BEING MOUNTED COAXIALLY WITHIN SAID BODY, GAS CHAMBER MEANS WITHIN SAID PROJECTILE HAVING A PLURALITY OF PORTS IN THE REAR WALL THEREOF FOR ESTABLISHING COMMUNICATION WITH THE INTERIOR OF THE CHAMBER MEANS, AND VALVE MEANS IN EACH OF THE PORTS ADAPTED TO TRAP EXPLOSION GASES UNDER PRESSURE IN SAID CHAMBER MEANS DURING THE FLIGHT OF SAID PROJECTILE, SAID PLUG ADAPTED TO BE DRIVEN FROM THE REARWARD POSITION IN ENGAGEMENT WITH A REAR WALL OF SAID GAS CHAMBER MEANS TO THE FORWARD POSITION DURING THE FLIGHT OF SAID PROJECTILE BY THE PRESSURE OF SAID TRAPPED GASES.