is reached by a direct conduct 5 by the powder supplied by a continuous feeding system 7 not shown the dosage chamber 2 being connected to the barrel 1 by a direct conduit 4 the dosage chamber 2 is basically an expansion chamber which communicates with the barrel 1 of the gun through a direct tubular conduit 4 of reduced diameter so that the pressure wave advancing through the barrel 1 passes to the communication conduit 4 and reaches the dosage chamber 2 the detonation gases which reach the dosage chamber 2 undergo a sudden expansion which fills the chamber with gas blocking the entry of the powder feeding conduct 5 in this way it is possible to cyclically interrupt the feeding of powder from the continuous feeder 7 and thus it is possible to control the amount of powder dosed in the chamber and consequently the amount of powder injected to the barrel in each detonation cycle the sudden expansion of the gas in the dosage chamber 2 creates a turbulence which produces the fluidization of all the powder contained in the dosage chamber 2 so that the auction process which follows the detonation carries all the powder contained in the chamber injecting it into the barrel 1 the fluidization.