Abstract: A device used especially in a large caliber weapon for controlling the train of motion of an ammunition unit during the ramming thereof in the weapon, and of the case of the ammunition unit on firing of the gun includes an impact arrangement which upon ramming of the ammunition unit enter into interaction with and retard the ammunition unit. An energy storing device is chargeable through the impact with kinetic energy existing in the retarding ammunition unit. In response to energy transmitted from the energy storing device the closing of the breech block is activated. The breech block in the closed position retains the case of the ammunition unit during the firing and during a predetermined portion of the rearwardly directed movement in the gun effected on firing. The impact arrangement includes an impact member interactable with a flange on the case and displaceable in the longitudinal direction of the gun, and an impact spring means interactable with the impact member and with an impact piston.