M61 Vulcan
The GAU-4 20mm Vulcan (with two models, designated M61A1 and M61A2) is a hydraulically driven, six-barreled, rotary action, air cooled, electrically fired gatling gun with selectable rates of fire of either 4000 or 6000 rounds per minute.
Mounted Vulcan
The gun is mounted on F-104, F-105, F-106 (later models), F-111, F-4, B-58, B-52H, F-15, F-16, Italian AMX Internationl AMX, F-22, F-14 and F/A-18 aircraft, and is used for short-range air-to-air combat with a secondary purpose being strafing ground targets. It was developed in 1946 by the United States Army Ordnance Research and Development Service, and manufactured by General Electric. Its first operational use was in the F-104. The current model is the M61A1, which uses a linkless 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, approximately 100 rounds per second, helps to insure a hit even in high-speed deflection shooting.
The M61A1 weighs about 275 lb (125 kg), but the feed system weighs 300-350 lb (140-160 kg), depending on the application, not counting the ammunition drum and ammunition. Some aircraft use the lightweight M61A2, which has thinner barrels to reduce mass. The M61A2 weighs 205 lb (93 kg), and has a rate of fire of 6600 rounds per minute.
A disadvantage of the M61 is that the bulk of the weapon, its feed system, and ammunition drum makes it difficult to fit it into a densely packed airframe. The ballistic characteristics of the 20mm (M50) ammunition are also poor: muzzle velocity, at about 3200 fps, is good, but the rounds loose energy fairly quickly, resulting in marginal killing power and accuracy. Some experts also feel that despite the high rate of fire, the Gatling-type weapon is hampered by the time it takes for the weapon to spin up to its maximum rotation speed (about 0.5 second). As a result, a one-second burst only fires about 70-75 rounds, which some experts feel is not enough of an advantage over revolver cannon like the ADEN/DEFA 30mm weapons to justify the additional weight and complexity. Efforts to develop a higher-caliber replacement for the M61, such as the five-barrel GAU-12 25mm gun used in the AV-8B Harrier, have thus far had limited success.
The weapon's current contractor is General Dynamics M197 Gatling gun
