is still in service, as well as many adaptions, such as the Japanese Ho-103 aircraft machine gun during World War II. Another legendarily reliable heavy machine gun is the British Vickers machine gun, based on the Maxim machine gun design, which saw service both on the air and ground during World War I and World War II. Due to their disadvantages, water-cooled weapons have gradually been replaced by much lighter air-cooled weapons. For weapons mounted on aircraft, no cooling device is necessary due to the outside air cooling the weapon as the aircraft is moving. Consequently, aircraft-mounted machine guns, autocannon or Gatling-type guns can sustain fire far longer than ground-based counterparts, firing close to their cyclic rate of fire. However, due to the weight of the ammunition, sustained fire is constrained by ammunition payload, as many aircraft cannons only carry enough ammunition for a few seconds' worth of firing; for example, the F-16 Falcon and its variants carry 511 rounds of 20mm ammunition, and the F-22 Raptor carries a similar amount at 480 rounds, which equates to roughly 5 seconds of firing at the M61 Vulcan's 6000 rpm (100 rounds per second) cyclic rate. (Some aircraft, due to the purpose of the design, do carry more, such as the GAU-8 Avenger mounted on the A-10 Thunderbolt, which carries 1,150 rounds of ammunition sufficient for 17 seconds of firing). Another factor influencing rate of fire is the supply of ammunition. At 50 rps (3,000 rpm), a five-second burst from an M134 Minigun would use approximately of 7.62 mm ammunition; this alone would make it an impractical weapon for infantry who have to carry a reasonable supply of ammunition with them. For this and other reasons, weapons with such high rates of fire are typically only found on vehicles or fixed emplacements. See also Multiple-barrel firearm References Ammunition Firearm actions Firing