7.62mm M134 Minigun

This weapon is based on the Gatling gun principle in which a high rate of fire is achieved by having a number of rotating barrels which fired in turn when the 12 o'clock position was reached.

The first Gatling gun was made in 1862 so possibly the progress made in the last 100 plus years is not as great as some would believe. The original Gatling gun was hand-cranked and could produce a cyclic rate of 1000 rounds per minute for a very brief period. The delays in loading etc. normally meant about 250 rounds per minute was the optimum.

The Minigun is driven by a 28 V DC or 115 V AC electric motor and produces a steady rate of fire which varies according to the type from between 2000 and 6000 rounds per minute as a top rate, down to 300 rounds per minute as the slowest rate of fire. At a steady 6000 rounds per minute the drive motor draws 130 A. The gun itself consists of four groups: the barrel group, gun housing; rotor assembly and bolt assembly.

Barrel Group

The six 7.62 mm barrels fit into the rotor assembly and each is locked by a 180° turn. They pass through the barrel clamp which grips the barrel using a special tool to secure the bolt. The barrels are normally parallel but there are other clamps available which are designed to produce varying dispersion patterns by ensuring that the barrels converge at some selected range.

Gun Housing

This is a one piece casting which holds the rotor assembly and provides a mounting for the `safety sector' and the guide bar. The function of these two components will be mentioned later. There is an elliptical cam path on the inner surface in which the bolt bearing roller runs.

Rotor Assembly

This is the main structural component of the gun and is supported in the gun housing by ball bearings. The front part of the rotor assembly holds the six barrels. Six bolt tracks are cut into the rotor and six removable tracks are bolted onto the ribs on the rotor. Each bolt track carries an S-shaped triggering cam which cocks and fires the firing pin of one bolt.

Bolt Assembly

There are six bolts each of which is mated to a barrel and lock into the barrel by means of a rotating head: when each is unlocked and withdrawn from the barrel the empty case is pulled out by a fixed extractor. The firing pin is spring operated and carries a projection or `tang' at the rear end. This tang engages the S-shaped triggering cam on the rotor. The side slots on the bolt engage in the bolt tracks of the rotor and this causes the bolt to move around with the rotor.

Operation

The red master switch cover must be elevated to expose the switch which controls all the electrics. The firing button on the left-hand trigger grip starts the rotor assembly and barrel assembly rotating in an anti-clockwise direction viewed from the rear. As the rotor assembly turns, the roller on each bolt follows the elliptical cam path on the inner surface of the gun housing. Each bolt in turn picks up a live round from the guide fingers of the guide bar.

As the bolt is carried round, the roller, working in the grove, moves the bolt forward to chamber the round. The bolt-head is now rotated by the cam path in the bolt body and locks into the barrel. The firing pin has been cocked by the tang action in the triggering cam in the rotor and at the top position of the bolt the S-shaped groove releases the firing pin and the round is fired.

The elliptical cam path in the gun housing has a flat profile, or dwell profile, which holds the bolt locked until the bullet has gone and the pressure has dropped to a safe level. The bolt assembly roller enters the reverse segment of the path and the bolt-head is unlocked. The cam path carries the bolt to the rear, extracting the empty case which is pushed away by the guide bar and ejected. The bolt has now passed through a 360° cycle and is ready to pick up another live round. All six bolts repeat the same procedure in sequence.

Ammunition boxes carry a normal load of 4000 linked rounds. This is pulled up by a plastic chute to the gun. If the length of tubing exceeds five feet (1.5 metres) or the radius of the curve is small it is advisable to have another motor on the top of the ammunition boxes driving a sprocket which helps by pushing the belted ammunition up to the gun.

It will be noted that since the entire gun is driven by an external source, a misfired round is simply ejected and thrown down with the empties either into a box or more usually out over the side.

It is equally possible to use unlinked ammunition and feed it up from the boxes.

When the gun ceases firing the bolts cease to pick up from the guide bar and the bolts close on an empty chamber. Thus there is no danger of a cock-off during the second it takes the barrels to come to rest.