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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.〔Julio S. Las Armas Modernas de Infantería, Abril de 1953〕 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, as a missile or rocket would. Nevertheless, there are also ''boost-after-launch'' rocket-propelled projectiles available for modern recoilless rifles. Normally used for anti-tank roles, the first effective system of this kind was developed during World War II by William Kroeger and Clarence Musser.〔U.S. Patent No. 2,466,714, Recoilless Firearm and Ammunition, Filing date: May 20, 1944, Inventors: William J. Kroeger, Clarence Walter Musser〕 Because 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 cannons, 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, as well as with some light infantry and infantry fire support units. 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 120 mm 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. ==Design== The typical recoilless gun functions very much like a conventional gun. The projectile and propellant are supplied as a single round and loaded into the breech. When fired, however, instead of all the propellant blast following the projectile out the barrel, a large portion is allowed to escape to the rear, gaining a rearward directed momentum which is nearly equal to the forward momentum of the projectile. This balance of momenta ensures that the momentum of the rifle/projectile/exhaust gas system is conserved without imparting much momentum (recoil) to the rifle itself. Since recoil has been mostly removed, the heavy and complex gun carriage and recoil damping mechanism can be dispensed with. Despite the name, it is rare for the forces to completely balance, and real-world recoilless rifles do recoil noticeably (with varying degrees of severity). Recoilless rifles are maintenance-intensive weapons, and if the breech and gas ports are old, damaged, plugged, or poorly maintained, the recoil-damping effect can be reduced or lost altogether, leading to dangerously powerful recoil. Conversely, if a projectile becomes lodged in the barrel for any reason, the entire weapon will recoil forward, in the manner of a rocket. Unlike a rocket launcher, which fires fin-stabilized rockets from a smooth bore, recoilless rifle rounds resemble conventional artillery shells. They generally have a pre-engraved rifling band to engage the rifled launch tube, spin-stabilizing the projectile, hence the term "rifle". The "case" area of the shell can be perforated to vent the propellant gases, which are then directed to the rear, as the base of the shell disintegrates. Since venting hot gases to the rear can be dangerous in confined spaces, some recoilless guns, such as the Armbrust and MATADOR, use a combination of a countershot, smoothbore barrel, and pistons to avoid both recoil and back blast. The fin stabilized Armbrust "cartridge" contains the propellant charge between two pistons with the warhead in front of one, facing forward, and an equal countermass of shredded plastic in front of the other piston. On firing, the propellant expands rapidly, pushing the pistons outward. This pushes the projectile forwards towards the target and the countermass backwards providing the recoilless effect. The shredded plastic countermass is quickly slowed by air resistance and is harmless at a distance more than a few feet from the breech. The pistons jam at the ends of the barrel, trapping the hot propellant gases inside. All this allows safe firing in enclosed spaces. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「recoilless rifle」の詳細全文を読む スポンサード リンク
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