1. A PROJECTILE COMPRISING A CASING, A TUBULAR TAIL WITH ITS FRONT PORTION FIXED SOLIDLY TO THE REAR OF SAID CASING, THE REAR PART OF SAID TAIL HAVING A SMALLER INSIDE DIAMETER THAN THE CORRESPONDING INSIDE DIAMETER OF SAID FRONT PORTION, A TUBULAR PISTON INSIDE SAID TAIL, A REARWARD PORTION IN SAID PISTON AT THE REAR OF SAID TAIL, SAID PISTON HAVING A FRONT END WITH AN OUTER DIAMETER CORRESPONDING TO THE INNER DIAMETER OF SAID FRONT PORTION, A STABLIZING EMPENNAGE MOUNTED AROUND THE REARWARD PORTION OF SAID PISTON, A LONGITUDINAL EXPANSION CHAMBER IN SAID TUBULAR PISTON, A PROPULSIVE CARTRIDGE INSIDE SAID CHAMBER AND CLOSING MEANS AROUND SAID PISTON FOR HERMETICALLY CLOSING SAID EXPANSION CHAMBER DURING THE TRAVEL ALONG ALL THE TRAJECTORY OF SAID PROJECTILE.