A recoilless rifle (RCLR) or recoilless gun is a type of lightweight tube artillery that is designed to allow some of the propellant gases to escape out the rear of the weapon at the moment of ignition, creating forward thrust that counteracts some of the weapon's recoil. This allows for the elimination of much of the heavy and bulky recoiling mechanisms of a conventional cannon while still enabling the unit to fire a powerful projectile. Besides this, the lower pressures involved allow thinner walled and lighter tubes, lowering further the weight of the cannon. Technically, only devices that use a rifled barrel are recoilless rifles. Smoothbore variants are recoilless guns. This distinction is often lost, and both are often called recoilless rifles.