Miniguns M134 7.62mm Minigun The Air Force GAU-2B/A (Army M134) 7.62mm "minigun" was designed to provide a light weight high rate of fire armament package for use on helicopters and light fixed-wing aircraft. The basic M61 Vulcan has been simplified and redesigned to fire percussion primed 7.62mm ammunition. The basic M134 can be readily modified to fire other smaller caliber ammunition, such as the XM214 5.56mm "mini-minigun". The GAU-17/A utilized on the UH-1N, H-3, and H-60 aircraft, is a crew served, electrically driven, 6 barreled, rotary action, percussion fired weapon, with a maxi-mum rate of fire of 6000 rounds per minute. In the current crew served application the rate of fire is selectable at either 2000 or 4000 rounds per minute. In the UH-1N DAS configuration the gun can be fixed forward and remotely fired by the pilot. The components that make up the GAU-17/A gun system consist of a gun control assembly with electrical cables, gun drive motor, a MAU-201/A or a MAU-56 delinking feeder, flexible ammunition feed chutes and an ammunition storage system. The ammunition storage system has a capacity of 4000 rounds of linked 7.62mm percussion primed ammunition. The M134 minigun was used on the M21, M27, XM50, and Emerson MINI-TAT on the UH-1 "Huey", OH-6A Cayuse, and OH-58A Kiowa, XM18E1, M28 series, and XM64 on the AH-1G and MOD AH-1S "Huey" Cobra, XM53 on the AH-56A Cheyenne, and on a wide variety of U.S. Army and U.S. Air Force light fixed-wing aircraft. The M134 is also used on a number U.S. Army special operations aircraft. Components of the M134 minigun are the rotor assembly, six bolt assemblies, six removable bolt tracks, gun housing assembly, rear gun support, six barrels, barrel clamp assembly, safing sector, housing cover, and two quick-release pins. As the rotor turns within the stationary housing cover, the bolt assembly rollers follow the main cam path of the housing cover, causing the bolt assemblies to move along the accommodating tracks. Each barrel is mounted in the barrel clamp assembly, in a fixed position, in alignment with a bolt assembly. M61A1/M61A2 20mm Vulcan The M61A1 utilized by the F-14 and F/A-18 aircraft is a hydraulically driven, 6 barreled, rotary action, air cooled, electrically fired weapon, with selectable rates of fire of either 4000 or 6000 rounds per minute. The M61A2 20mm light weight gun is utilized in the F/A-18 aircraft only. The gun system is mated to a linkless ammunition storage and handling system. The F-14 has a capacity of 676 rounds while the F/A-18 has a capacity of 578 rounds of 20mm linkless M-50 or PGU series electrically primed ammunition. World War II fighters and bombers were commonly equipped with Browning M2 heavy barrel .50 cal. machine guns which had a maximum firing rate of 1,200 spm. The Gatling gun had exceeded that rate of fire in 1880. In 1946, U.S. Army Ordnance Research and Development Service engineers dusted-off the old Gatling principle and adapted it to create the 6,000 spm M61 series Vulcan 20mm Gatling gun. The Gatling principle permitted a high rate of fire while reducing heat and barrel erosion. In June 1946, the General Electric Company was awarded the contract for "Project Vulcan". In 1950, GE delivered ten initial model A .60 cal. T45 guns for evaluation. Thirty-three model C T45 guns were delivered in 1952 in three calibers: .60 cal., 20mm, and 27mm, for additional testing. After extensive testing, the T171 20mm gun was selected for further development. In 1956 the T171 20mm gun was standardized by the U.S. Army and U.S. Air Force as the M61 20mm Vulcan aircraft gun. The M61 20mm Vulcan is an externally powered, six-barrel, rotary-fire gun having a rate of fire of up to 7200 spm. The firing rate is selectible at 4,000 spm or 6,000 spm. The gun fires standard electrically primed 20mm ammunition. The M61A1 is hydraulically or ram-air driven, electrically controlled, and uses a linkless ammunition feed system. Each of the gun's six barrels fires only once during each revolution of the barrel cluster. The six rotating barrels contribute to long weapon life by minimizing barrel erosion and heat generation. The gun's rate of fire, essentially 100 rounds per second, gives the pilot a shot density that will enable a "kill" when fired in one-second bursts. The M61 20mm cannon is a proven gun, having been the US military's close-in weapon of choice dating back to the 1950s. The F-104, F-105, later models of the F-106, F-111, F-4, B-58, all used the M61, as does the Air Force's F-15 , F-16 and F-22, and the Navy's F-14 and F/A-18. The internally mounted 20mm cannon system is common to all versions of the F-15. This system combines the widely used (F-4, F-16, F-18) M61 cannon with 940 rounds (A through D models) or 500 rounds (E model) of ammunition. The cannon can be loaded with target practice, armor piercing, or high explosive incendiary rounds. The primary use of the cannon is in the extremely short range (less than 2000 feet) air-to-air environment, where more sophistacated air-to-air missiles are ineffective. Alternately, the cannon has limited usefulness in a ground strafing role. The M61A2 is a lightweight version of the M61A1. Most of the weight savings was achieved by machining down the barrel thickness. GAU-8/A Avenger The AN/GAU-8 30mm Avenger seven-barrel gatling gun, mounted only on the A-10 attack jet, is a 30mm, 7 barrel gattling gun used primarily in the air to ground role as a soft target killer and tank buster. This aircraft is used for close-air support in attacking ground threats such as armored tanks and vehicles, and also serves as a forward air control observer for sighting ground threats and directing air strikes against enemy targets. The gun, mounted in the fuselage nose of the A/OA-10 Thunderbolt, is produced by [ex General Electric] Martin Marietta Armament Systems. According to some sources, the GAU-8 fires 1,800 rounds per minute, with the higher 4200 rd/min rate having been deleted in the 1980s. However, the A-10 can only fire in high rate, which is 3900 rounds per minute. Low rate went out with the use of the batelle gas diverting device, and although the A-10 no longer uses the batelle device, the limit on high rate only has remained, since it made no tactical sense to fire in low rate and have to spend that much more time on final to get the same number of rounds on target. The gun fires a mix of both high explosive incendiary (HEI) and armored piercing incendiary (API) ammunition. The PGU-13/B HEI High Explosive Incendiary round employs a standard M505 fuze and explosive mixture with a body of naturally fragmenting material that is effective against lighter vehicle and material targets. The PGU-14/B API Armor Piercing Incendiary round has a lightweight body which contains a sub-calibre high density penetrator of Depleted Uranium (DU). In addition to its penetrating capability DU is a natural pyrophoric material which enhances the incendiary effects. The PGU-15/B TP Target Practice projectile simulates the exterior ballistics and provides a ballistic match to the HEI round and is used for pilot training. A typical combat load for the GAU-8 would include 1,100 rounds of 30mm high explosive or armor piercing ammunition. The 30mm API is mixed with 30mm High Explosive Incendiary (HEI) at the factory and is called Combat Mix Ammunition. The ratio of API to HEI rounds in the Combat Mix is 4:1. Combat mix is a sequential mixture of DU and HEI rounds in which 1 HEI round followed by 4 DU rounds are fired by the AN/GAU-8 gatling gun. DU is the primary munition for the A/OA-10 in a combat environment. Depleted uranium results from the enriching of natural uranium for use in nuclear reactors. Natural uranium is a slightly radioactive metal that is present in most rocks and soils as well as in many rivers and sea water. Natural uranium consists primarily of a mixture of two isotopes (forms) of uranium, Uranium-235 (U235) and Uranium-238 (U238), in the proportion of about 0.7 and 99.3 percent, respectively. Nuclear reactors require U235 to produce energy, therefore, the natural uranium has to be enriched to obtain the isotope U235 by removing a large part of the U238. Uranium-238 becomes DU, which is 0.7 times as radioactive as natural uranium. . Since DU has a half-life of 4.5 billion years, there is very little decay of those DU materials. When manufactured as 30mm rounds, each DU projectile contains approximately 4,650 grains [0.66 pounds (lbs)] of extruded DU, alloyed with 0.75 weight percent titanium. The projectile is encased in a 0.8 mm-thick aluminum shell as the final DU round. During Operation DESERT STORM the Air Force fired 30mm Armor Piercing Incendiary (API) munitions using a depleted uranium [DU] penetrator slug from the GAU-8 Gatling gun mounted on the A-10 Aircraft. The 148 A-10s that deployed to Saudi Arabia flew 8,077 combat sorties. The Air Force fired a total of 783,514 rounds of 30mm API in the Gulf War. Since each round contains approximately 0.66 pounds of DU, the Air Force expended a total of 259 tons of DU in the Gulf. The armor-piercing capability of the DU projectiles fired from A/OA-10s proved exceptionally effective in countering threats from the Iraqi tanks so that a successful ground offensive could then be achieved. At times 30mm DU rounds misfire in the A-10’s GAU-8 cannon. These "hangfires" have to be cleared and removed from the gun barrel, potentially exposing ground crews to airborne DU. Technical data available to maitenance crews does not provide an accurate means for determining the status of rounds in an unsafe/jammed gun, and revisions are in progress. Source: FAS.org / posted by Flyboy