portions 30 to be lost in the total number of reactions that is the various gas pressure developments act on projectile 14 and the remaining components of the weapon only with an average gas pressure it should be noted from fig1 that the region in which recuperator spring 42 is mounted is protected by seals shown but not numbered thereby preventing high pressure detonation gasses from entering this region this facilitates the opening movement of pump piston 25 after a shot has been fired recuperator spring 42 will move pump piston 25 back into its closed position and thus make propellant chamber 22 ready for a new filling process through valves not shown the further embodiment shown in fig2 and 3 illustrates the use of the invention for example for a small caliber liquid propellant cannon 12 in contrast to the embodiment shown in fig1 projectile 16 is not surrounded by the propellant chamber instead projectile 16 is disposed ahead of propellant chamber 24 in the gun barrel the propellant chamber 24 is provided in a breechblock housing 13 and is closed at the tail end thereof by a breechblock 20 screwed into housing 13 the other end of propellant chamber 24 is initially closed by a pump piston 26 as shown in fig2 the total length of propellant chamber 24 is designated 1 in fig2 pump piston 26 is mounted so as to be axially movable for a stroke of distance a for this purpose pump piston 26 includes a.