The Crusader III was issued with either a Mark 3 or Mk 5 6pdr gun . The Mk 3 had a thicker , shorter barrel ( 100.95 inches ) usually with a sleeve over the threads for the un used muzzle break ( like some versions of the US 76mm Sherman ) . The Mk 5 was a skinner , longer barrel ( 116.95 inches ) with a short stubby counterweight on the muzzle .