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. 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. Though it is similar in form and appearance to a rocket launcher, it fires modified artillery shells, not rockets. The key difference from rocket launchers (whether man-portable or not) is that the projectile of the recoilless rifle has no propulsion of its own - once out of the rifle, it behaves as a normal artillery shell and does not accelerate further, like a missile or rocket would. Nevertheless there are also boost-after-launch rocket-propelled projectiles available for modern recoilless rifles.
Since some projectile velocity is inevitably lost to the recoil compensation backblast, recoilless rifles tend to fire a fairly heavy explosive shell with less range than traditional cannon, although with a far greater ease of transport, making them popular with paratroop, mountain warfare and special forces units where portability is of particular concern. Although the greatly diminished recoil allows many smaller and newer versions to be shoulder-fired by individual infantrymen, the majority of recoilless rifles in service are mounted on light tripods and intended to be carried by a small 2 or 3 man crew. The largest versions, such as the British 120mm L4 MoBAT and L6 Wombat, retain enough bulk and recoil to be restricted to a firm vehicular mount, such as on a jeep, truck or armored personnel carrier.
The Carl Gustav (also Carl-Gustaf and M2CG; pronounced "Carl Gustaf") is the common name for the 84 mm man-portable reusable multi-role recoilless rifle produced by Saab Bofors Dynamics (formerly Bofors Anti-Armour AB) in Sweden. The first prototype of the Carl Gustaf was produced in 1946, and while similar weapons of the era have generally disappeared, the Carl Gustaf remains in widespread use today. British troops refer to it as the Charlie G, while Canadian troops often refer to it as the 84, Carl G or Carlo. In U.S. military service it is known as the M3 Multi-role Anti-armor Anti-tank Weapon System (MAAWS) or Ranger Antitank Weapons System (RAWS), but is often called the Gustav or the Goose or simply the Carl Johnson by U.S. soldiers. In Australia it is irreverently known as Charlie Gusto or Charlie Gutsache (guts ache, slang for stomach pain). In its country of origin it is officially named Grg m/48 (Granatgevär or grenade rifle, model 48).