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The High-Low system also referred to as the "High-Low Pressure system", the "High-Low Propulsion System", and the "High-Low projection system", is a design of cannon and antitank launcher using a smaller ''high-pressure chamber'' for storing the propellant. It enables a much larger projectile to be launched without the heavy equipment typically required for large caliber weapons. When the propellant is ignited, the higher pressure gases are bled out through vents (or ports) at reduced pressure to a much larger ''low pressure chamber'' to push the projectile forward. With the High-Low System a weapon can be designed with reduced or negligible recoil. The High-Low System also allows the weight of the weapon and its ammunition to be significantly reduced. Manufacturing cost and production time are drastically lower than standard cannon or other small-arm weapon systems firing a projectile of the same size and weight. It has a far more efficient use of the propellant, unlike earlier recoilless weapons, where most of the propellant is expended to the rear of the weapon to counter the recoil of the projectile being fired.〔Ian V. Hogg, ''The Guns 1939-45'', page 155, Ballantine Books, 1970. 〕 ==Origin== In the final years of World War II, Nazi Germany researched and developed low-cost antitank weapons. Large antitank cannon firing high velocity projectiles were the best option, but expensive to produce as well as requiring a well trained crew. They also lacked mobility on the battlefield once emplaced. Antitank rocket launchers and recoilless rifles, while much lighter and simpler to manufacture, gave the gunner's position away and were not as accurate as antitank cannon. Recoilless rifles used a huge amount of propellant to fire the projectile, with estimates ranging from only one-fifth to one-ninth of the propellant gases being used to push the projectile forward.〔With the simple one man Panzerfaust the ratio was even higher.〕 The German military asked for an antitank weapon with performance in-between that of the standard high velocity cannon and the cheaper rocket and recoilless infantry antitank weapons. They also stipulated that any solution had to be more efficient in the use of propellant as German war industry had reached maximum cannon propellent production capacity. In 1944, the German firm Rheinmetall-Borsig came up with a completely new concept for propelling a projectile from cannon, which, while not recoilless, greatly reduced recoil and drastically reduced the manufacturing cost. This concept was called the ''Hoch-und-Niederdruck System'' which roughly translates to "High-Low Pressure System". With this system, only the very back of the cannon's breech had to be reinforced against the high firing pressures. Rheinmetall designed an antitank cannon using their "High-Low Pressure System" that fired a standard general purpose HE 8.1-cm mortar bomb which had been modified to function as an antitank round with a shaped charge.〔Today, shaped charges are commonly called HEAT warheads or HEAT projectiles. HEAT is an acronym for "High Explosive, Anti-Tank".〕 Normally, a mortar bomb cannot be fired from a cannon, because their thin walls can not endure the high stress forces upon firing from a cannon. The 8.1-cm round was mounted on a rod which was fixed to a round steel plate with eight holes in it. A shear pin held the round to the rod. The round and the plate were fitted at the mouth of a cut-down cannon shell casing which contained two propellant bags. On firing, the pressure would build up in the shell casing, which along with the reinforced breech, acted as the "High Pressure Chamber" and bled out the steel plate holes at half the pressure to the thinner walled cannon barrel which acted as the "Low Pressure Chamber". Unlike standard cannon, in which the propellant "kicks" the projectile out the barrel with an almost instant acceleration to maximum muzzle velocity, the Rheinmetall concept "shoved" the projectile out the barrel at a constantly increasing muzzle velocity. There was recoil, but nowhere near the recoil of the 5-cm and 7.5-cm antitank cannons being used at that time by the German forces, which required a heavy constructed carriage, and both a heavy and complex hydraulic recoil mechanism as well as a muzzle brake to contain the massive recoil on firing. The Rheinmetall solution required only a lightweight recoil unit and muzzle brake. The 81mm weapon weighed significantly less than even the then obsolete 50mm cannon and Allied 57mm guns, less than a one seventh the weight of the 88mm Pak it was to supplement, and less than a tenth of the weight of the famous 88mm anti aircraft gun turned anti tank weapon.〔8.8 cm Pak 43〕〔88mm flak gun〕〔Ordnance QF 6-pounder〕〔5 cm Pak 38〕 The only major drawback was its maximum range of 750 meters (in direct fire against tanks), but this was offset by an armor penetration of 140 mm and no telltale back-blast. Over 500 meters, this is superior to both the German long barrel 75mm cannon,〔7.5 cm Pak 40〕 and the American 76mm gun, even when equipped with tungsten HVAP armor piercing rounds. 〔76 mm gun M1〕 The Germans ordered the Rheinmetall gun into production, designating it as the 8-cm Panzer Abwehr Werfer 600 (PAW 600).〔In the last months of the war, the German Army re-designated it the Panzerwurfkanone 8H63 (PWK 8H63).〕 Only about 250 were produced before the war's end. None were reported to have seen combat.〔 The High-Low system developed on the PAW 600 was later used to propel the shells for the ubiquitous American 40mm grenade launcher.〔Department of the Army, (''Field Manual FM 23-31'' ), page 21-22, April 1965.〕 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「High–low system」の詳細全文を読む スポンサード リンク
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