Kirov Plant
An experimental model was ready in 1957. Its chassis (Object 273), was designed and built by the Kirov Plant. Its 20-meter barrel allowed it to fire 750 kg rounds up to 45 km. Due to its complexity of loading it had a relatively low rate of fire—one round every five minutes. Field tests showed various drawbacks of the entire design (the recoil was too strong for many components: it damaged drive sprockets, ripped the gear-box away from its mountings, etc.) and the sheer length rendered it incredibly difficult to transport.