M256 gun. S. M1A1 Abrams main battle tanks. It is primarily used by the M1 Abrams main battle tank. The M256 is an American 120 mm smoothbore tank gun. It is a licensed derivative of the German Rheinmetall Rh-120 gun, adapted with an American-designed mount and breech mechanism while retaining the original L/44 barrel design for compatibility with NATO Dec 26, 2025 · The M256 120mm Po was selected as the flagship weapon of Abrams in 1979, but the improved ammunition to be used in this gun was not completely developed, and the initial M1 Abrams was armed with a 105mm M68 due to the delay in the deployment by 1984. The Rheinmetall-designed 120-mm smoothbore tank gun is the main armament for the German Leopard 2 and U. The actual gun tube is a one-piece steel forging, cold worked with a smoothbore for the 120 mm ammunition. It uses a German-designed Rh-120 L44 gun tube and combustible cartridges with an American-designed mount, cradle and recoil mechanism. The Rheinmetall-designed 120-mm M256 smoothbore tank gun is the main armament for the German Leopard 2 and U. M1A1 and M1A2 series of main battle tanks. hiwt fbtp phh ysv hlwuak cle rmvwga lpto cehkn mbwn