 The Rheinmetall 120 mm gun is a smoothbore tank gun designed and produced by the West German Rheinmetall @-@ <unk> AG company , developed in response to Soviet advances in armor technology and development of new armored threats . Production began in 1974 , with the first version of the gun , known as the L / 44 as it was 44 calibers long , used on the German Leopard 2 tank and soon produced under license for the American M1A1 Abrams and other tanks . The American version , the M256 , uses a coil spring recoil system instead of a hydraulic system . The 120 @-@ millimetre ( 4 @.@ 7 in ) gun has a length of 5 @.@ 28 metres ( 17 @.@ 3 ft ) , and the gun system weighs approximately 3 @,@ 317 kilograms ( 7 @,@ 313 lb ) . 
