M134 Minigun


The M134 Minigun is an American 7.62×51mm NATO six-barrel rotary machine gun with a high rate of fire. It features a Gatling-style rotating barrel assembly with an external power source, normally an electric motor. The "Mini" in the name is in comparison to larger-caliber designs that use a rotary barrel design, such as General Electric's earlier 20 mm M61 Vulcan, and "gun" for the use of rifle ammunition as opposed to autocannon shells.
"Minigun" refers to a specific model of weapon that General Electric originally produced, but the term "minigun" has popularly come to refer to any externally powered rotary gun of rifle caliber. The term is sometimes used loosely to refer to guns of similar rates of fire and configuration, regardless of power source and caliber.
The Minigun is used by several branches of the U.S. military. Versions are designated M134 and XM196 by the United States Army, and GAU-2/A and GAU-17/A by the U.S. Air Force and U.S. Navy.

History

Background: electrically driven Gatling gun

The ancestor to the modern minigun was the hand cranked mechanical Gatling gun invented in the 1860s by Richard Jordan Gatling. He later replaced the hand-cranked mechanism with an electric motor, a relatively new invention at the time. Even after Gatling slowed the mechanism, the new electrically powered Gatling gun had a theoretical rate of fire of 3,000 rounds per minute, roughly three times the rate of a typical modern, single-barreled machine gun. Gatling's design received U.S. Patent #502,185 on July 25, 1893. Despite his improvements, the Gatling gun fell into disuse after cheaper, lighter-weight, recoil and gas operated machine guns were invented; Gatling himself went bankrupt for a period.
During World War I, several German companies were working on externally powered guns for use in aircraft. One of these designs was the Fokker-Leimberger, an externally powered 12-barrel rotary gun using the 7.92×57mm Mauser round; it was claimed to be capable of firing over 7,000 rpm, but suffered from frequent cartridge-case ruptures due to its "nutcracker" rotary split-breech design, which is different from that of conventional rotary gun designs. None of these German guns went into production during the war, although a competing Siemens prototype, which was tried on the Western Front, scored a victory in aerial combat. The British also experimented with this type of split-breech during the 1950s, but they were also unsuccessful.

Minigun: 1960s–Vietnam

In the 1960s, the United States Armed Forces began exploring modern variants of the electrically powered, rotating barrel Gatling-style weapons for use in the Vietnam War. American forces in the Vietnam War, which used helicopters as one of the primary means of transporting soldiers and equipment through the dense jungle, found that their helicopters were vulnerable to small arms fire and rocket-propelled grenade attacks when they slowed to land. Although helicopters had mounted single-barrel machine guns, using them to repel attackers hidden in the dense jungle foliage often led to overheated barrels or cartridge jams.
To develop a more reliable weapon with a higher rate of fire, General Electric designers scaled down the rotary-barrel 20 mm M61 Vulcan cannon for 7.62×51mm NATO ammunition. The resulting weapon, designated M134 and known as the "Minigun", could fire up to 6,000 rounds per minute without overheating. The gun has a variable rate of fire, specified to fire at rates of up to 6,000 rpm with most applications set at rates between 3,000 and 4,000 rounds per minute.
The Minigun was mounted on Hughes OH-6 Cayuse and Bell OH-58 Kiowa side pods; in the turret and on pylon pods of Bell AH-1 Cobra attack helicopters; and on door, pylon and pod mounts on Bell UH-1 Iroquois transport helicopters. Several larger aircraft were outfitted with miniguns specifically for close air support: the Cessna A-37 Dragonfly with an internal gun and with pods on wing hardpoints; and the Douglas A-1 Skyraider, also with pods on wing hardpoints. Other famous gunship airplanes are the Douglas AC-47 Spooky, the Fairchild AC-119, and the Lockheed AC-130.

Dillon Aero minigun

The U.S. government had procured some 10,000 Miniguns during the Vietnam War. Around 1990, Dillon Aero acquired a large number of Miniguns and spares from "a foreign user". The guns kept failing to shoot continuously, revealing that they were actually worn-out weapons. The company decided to fix the problems encountered, rather than simply putting the guns into storage. Fixing failure problems ended up improving the Minigun's overall design. Word of Dillon's efforts to improve the Minigun reached the 160th SOAR, and the company was invited to Fort Campbell, Kentucky, to demonstrate its products. A delinker, used to separate cartridges from ammunition belts and feed them into the gun housing, and other parts were tested on Campbell's ranges. The 160th SOAR were impressed by the delinker's performance and began ordering them by 1997. This prompted Dillon to improve other design aspects including the bolt, housing and barrel. From 1997 to 2001, Dillon Aero manufactured 25–30 products per year. In 2001, it was working on a new bolt design that increased performance and service life. By 2002, virtually every component of the minigun had been improved, so Dillon began producing complete weapons with improved components. The guns were purchased quickly by the 160th SOAR as its standardized weapon system. The gun then went through the Army's formal procurement system approval process, and in 2003 the Dillon Aero minigun was certified and designated M134D. Once the Dillon Aero system was approved for general military service, Dillon Aero GAU-17s entered Marine Corps service and were well received in replacing GE's GAU-17s serving on Marine UH-1s.
The core of the M134D was a steel housing and rotor. To focus on weight reduction, a titanium housing and rotor were introduced, creating the M134D-T which had reduced weight from to. The gun housing had a 500,000-round lifespan before it wore out, which was far higher than a conventional machine gun's 40,000-round lifespan but lower than that of other rotary guns. A hybrid of the two weapons resulted in the M134D-H, which had a steel housing and titanium rotor. It was cheaper with the steel component and only heavier than the M134D-T, and restored its lifespan to 1.5 million rounds. The M134D-H is currently in use on various 160th Regiment platforms.
Dillon also created specialized mounts and ammunition-handling systems. Initially, mounts were made only for aviation systems. Then from 2003 to 2005, the Navy began mounting Dillon miniguns on specialized small boats. In 2005, the Naval Surface Warfare Center Crane Division procured guns to mount on Humvees. In Iraq, US Army Special Forces units on the ground were frequently engaged by opposition forces, so they mounted M134D miniguns on their vehicles for additional firepower. After several engagements the attackers seemed to avoid vehicles with miniguns. Later, the Special Forces units began concealing their weapons so opposition troops would not know they were facing the weapon; the regular Army units did the opposite, creating minigun mock-ups out of painted PVC pipes tied together to resemble barrels to intimidate enemies.

Garwood Industries minigun

Garwood Industries created the M134G version with several modifications to the original GE system. The optimum rate of fire was determined by Garwood to be around 3,200 rounds per minute. The M134G is being produced with this firing rate as well as 4,000 rpm and the previous standard 3,000 rpm rate. Garwood Industries made several other modifications to the 1960s Minigun design in order to meet modern-day military and ISO standards. This includes modifications to the drive motor, feeder and barrel clutch assembly.
From 2015 to 2017 Garwood Industries CEO Tracy Garwood collaborated with firearms dealer Michael Fox and weapons smuggler Tyler Carlson to supply miniguns to Mexican drug cartels. Garwood submitted false paperwork to the ATF claiming that some M134G rotor housings had been destroyed when they were actually sold to the gun-running ring. In 2017 federal agents raided Fox's home and recovered two of the rotor housings that Garwood had reported destroyed. A number of the rotor housings were shipped to Mexico and a completed M134G using a reportedly destroyed rotor housing was recovered from a cartel by Mexican law enforcement. Garwood claimed he did not know that the intended buyers were Mexican cartels although he was aware that they were to be used for illegal activity.

Design and variants

The basic minigun is a six-barrel, air-cooled, and electrically driven rotary machine gun. The electric drive rotates the weapon within its housing, with a rotating firing pin assembly and rotary chamber. The minigun's multi-barrel design helps prevent overheating, but also serves other functions. Multiple barrels allow for a greater capacity for a high firing rate, since the serial process of firing, extraction, and loading is taking place in all barrels simultaneously. Thus, as one barrel fires, two others are in different stages of shell extraction and another three are being loaded. The minigun is composed of multiple closed-bolt rifle barrels arranged in a circular housing. The barrels are rotated by an external power source, usually electric, pneumatic, or hydraulic. Other rotating-barrel cannons are powered by the gas pressure or recoil energy of fired cartridges. A gas-operated variant, designated XM133, was also developed, but was not put into production. It was to be nearly identical to the M134 but with ports that aligned with the piston drive in the center of the barrel cluster.
While the weapon can feed from linked ammunition, it requires a delinking feeder to strip the links as the rounds are fed into the chambers. The original feeder unit was designated MAU-56/A, but has since been replaced by an improved MAU-201/A unit.
File:U.S. Navy special warfare combatant-craft crewmen, Special Boat Team 22 conducts training 16 AUG 09.jpg|thumb|right|A U.S. Navy Special Warfare Combatant-craft Crewman on a SOC-R firing a Minigun at Stennis Space Center in Mississippi, August 2009.
The General Electric minigun is used in several branches of the U.S. military, under a number of designations. The basic fixed armament version was given the designation M134 by the United States Army, while the same weapon was designated GAU-2/A and GAU-17/A by the United States Air Force and United States Navy. The USAF minigun variant has three versions, while the US Army weapon appears to have incorporated several improvements without a change in designation. The M134D is an improved version of the M134 designed and manufactured by Dillon Aero, while Garwood Industries manufactures the M134G variant. Available sources show a relation between both M134 and GAU-2/A and M134 and GAU-2B/A. A separate variant, designated XM196, with an added ejection sprocket was developed specifically for the XM53 Armament Subsystem on the Lockheed AH-56 Cheyenne helicopter.
Another variant was developed by the USAF specifically for flexible installations, beginning primarily with the Bell UH-1N Twin Huey helicopter, as the GAU-17/A. Produced by General Dynamics, this version has a slotted flash hider. The primary end users of the GAU-17/A have been the USN and the United States Marine Corps, which mount the gun as defensive armament on a number of helicopters and surface ships. GAU-17/As from helicopters were rushed into service for ships on pintle mountings taken from Mk16 20 mm guns for anti-swarm protection in the Gulf ahead of the 2003 Iraq War - 59 systems were installed in 30 days. The GAU-17/A is designated Mk 44 in the machine gun series and is generally known as the Mk 44 when installed on British warships.
The weapon is part of both the A/A49E-11 armament system on the UH-1N; and of the A/A49E-13 armament subsystem on the USAF Sikorsky HH-60H Pave Hawk helicopter. The weapons on these systems feature a selectable fire rate of either 2,000 or 4,000 rpm. There is mention of a possible GAUSE-17 designation, in reference to the system when mounted on surface ships, though this would not follow the official ASETDS designation system's format.
US Army designationUS Air Force designationUS Navy designationDescription
XM134/M134GAU-2/AN/A7.62×51mm NATO GE "Minigun" 6-barreled machine gun
N/AGAU-2A/AN/AGAU-2/A variant; unknown differences
M134GAU-2B/AMk 25 MOD0GAU-2A/A variant; unknown differences
N/AGAU-17/AN/AGAU-2B/A variant; can be mounted to a variety of different craft, uses either an MAU-201/A or MAU-56/A delinking feeder.
N/AN/AMk 44Unknown differences
XM214 MicrogunN/AN/AScaled-down variant of the XM134 firing the 5.56×45mm NATO round. The U.S. military lost interest in the project, and it never entered mass production.
XM196N/AN/AM134/GAU-2B/A variant; housing modified by addition of an ejection sprocket; for use in the XM53 armament subsystem on the AH-56 helicopter