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 - 1 round every 5 minutes. Field tests showed various drawbacks of the entire design (the recoil was too strong for many components - it damaged drive sprockets, tore away the gear-box from its mountings, etc).