Abstract: A piston cylinder unit of an upwardly swinging pinile mounting necessary for the adjustment of the muzzle height of the gun barrel of a battle tank contains a bracking mechanism which becomes effective at firing at each upwardly swingable setting of the gun barrel. In this way it is possible to utilize the swinging motion of a gun mount arm carrying a gun barrel for the recoil energy release of the gun barrel. The barrel recoil energy of the gun barrel, and of the masses recoiling at the same time with the gun barrel, is thereby energy dissipatingly absorbed at the barrel recoil, after completing the free-running switching operation d of a known barrel recoil brake mechanism within a barrel recoil path c, jointly formed out of the recoil ranges a and b, on the one hand, by way of the piston cylinder unit over the gun mount arm swung back by an angle .alpha.