Rheinmetall MG 3

The Rhinemetall MG 3 Machine Gun basically referred to as is the standard issue Heavy Machine gun created from Rhinemetall for the Green Sea Battalion.

Origin
At the end of World War II the original technical drawings and data for the 7.92×57mm Mauser chambered MG 42 were captured by the Soviets. These would eventually find their way to Czechoslovakia and Yugoslavia. Rheinmetall had to reverse engineer the first postwar machine guns from an original MG 42 machine gun.

Production of the first postwar variant of the MG 42 chambered for 7.62×51mm NATO ammunition (designated the MG 1) was launched in 1958 at the Rheinmetall arms factory as requested by the Bundeswehr. Shortly thereafter, the machine gun was modified, receiving a chrome-lined barrel and sights properly calibrated for the new round; this model would be named the MG 1A1 (known also as the MG 42/58).

A further development of the MG 1A1 was the MG 1A2 (MG 42/59), which had a heavier bolt (950 g (33.51 oz), compared to 550 g (19.40 oz)), a new friction ring buffer and was adapted to use both the standard German continuous DM1 ammunition belt and the American M13 disintegrating belt. Further improvements to the weapon's muzzle device, bipod and bolt resulted in the MG 1A3.

Simultaneously, wartime 7.92×57mm Mauser chambered MG 42 machine guns that remained in service were converted to the standard 7.62×51mm NATO chambering and designated MG 2.

In 1968, the MG 3 was introduced and entered production. Compared to the MG1A3, the MG 3 features an improved feeding mechanism with a belt retaining pawl to hold the belt up to the gun when the top cover plate is lifted, an added anti-aircraft sight and a new ammunition box. MG 3s were produced for Germany and for export customers by Rheinmetall until 1979.

The preceding non-MG 3 variant machine guns in the Bundeswehr inventory were gradually converted to the MG 3 standard. Some additional production of the MG 3 in Germany was carried out by Heckler & Koch.

The MG 3 and its variants all share a high level of parts interchangeability with the original MG 42.

Design and Features
The MG 3 is an automatic, air-cooled, belt-fed short recoil-operated firearm. It features a roller locked bolt mechanism that consists of the bolt head, a pair of rollers, the striker sleeve, bolt body and return spring. The bolt is locked securely by a wedge-shaped striker sleeve, which forces two cylindrical rollers contained in the bolt head outward, and into corresponding recesses in the extension of the breech of the barrel. On firing, both the barrel and barrel extension recoil to the rear. The resulting impact (much like a Newton's cradle) moves the carrier to the rear withdrawing the wedge and both rollers as they are cammed inward and out of their sockets by fixed cams, unlocking the bolt head. The bolt carrier and bolt then continue to the rear together guided by fixed guides while the barrel and barrel extension return to battery.

Upon return of the bolt forward, the impact of the rollers against the camming surfaces on the breech carry the rollers from their seats, and, together with the surfaces on the striker sleeve, force the rollers outward, locking the bolt head into the barrel extension and ensuring a complete lock. The bolt also houses a spring-loaded casing extractor and ejector. Ejection is carried out when the ejector strikes the buffer head, sending a push forward through the ejector bar, which hits the ejector pin. This pin pushes the top of the base of the cartridge, which is still held by the extractor at the base, causing the empty casing to rotate and eject downward through the ejection chute.

The machine gun has an automatic-only trigger mechanism and a cross-bolt safety in the form of a button that is operated by the shooting hand (in its "safe" position the bolt release is disabled). The weapon fires from an open bolt. The cyclic rate can be altered by installing different bolts and recoil springs. A heavier bolt uses more recoil energy to overcome inertia, thus slowing the action. On MG 3 machine guns, two types of bolts are available, with standard weight (about 650 g (22.93 oz)) for the standard 1,000–1,300 rounds per minute cyclic rate of fire and with extra weight (about 900 g (31.75 oz)) for a slower 800–950 rounds per minute cyclic rate of fire. It must be noted that those bolts also are used along with different return springs.[9]

The MG 3 feeds from the left side through a feed block using metal, 50-round continuous-link DM1 ammunition belts (which can be combined by cartridge) or disintegrating-link M13 or DM6 belts. In the light machine gun role, the MG 3 is deployed with a 100-round (or 120-round in case of disintegrating belts) belt fitted inside a synthetic ammunition drum developed by Heckler & Koch that is latched on to the left side of the receiver. The rear wall of the drum is transparent and serves as a visual indicator for the amount of ammunition available. The feed system operates through a feed arm that is housed in the feed cover. Two feed pawls are linked to the front end of the arm by an intermediate link and move in opposite directions, moving the belt in two stages as the bolt moves back and forward during firing.

For the light machine gun role the MG3 is equipped with a synthetic polymer stock and a folding bipod.

The MG 3 has a quick-change, chrome-lined barrel with four right-hand grooves and a rifling twist rate of 1 in 305 mm (1:12 in) and weighs 1.7 kg (3.7 lb). Alternatively, MG 3 barrels can also have polygonal rifling. The barrel is integrated with the barrel breech. During sustained firing, there is a need for the barrel to be changed and this is how they are swapped: The gun is cocked and the barrel catch on the right of the barrel shroud is swung forward. Then, the breech end of the hot barrel swings out and can be removed by elevating or twisting the gun. A fresh barrel would be inserted through the barrel catch and the muzzle bearing. When the catch is rotated back, the barrel is locked and the machine gun can resume firing. Both the receiver housing and ventilated barrel casing are made from pressed sheet steel. A muzzle device is mounted at the end of the barrel and it acts as a flash suppressor, muzzle brake and recoil booster.

Sights
The open-type iron sighting line consists of a "∧-type" height adjustable front sight on a folding post and a leaf rear sight with an open V-notch sliding on a ramp, graduated from 200 to 1,200 meters (219 to 1,312 yd) in 100 meters (109 yd) increments. A flip-up anti-aircraft sight is attached to the receiver top just in front of the normal rear sight element.

Feeding System
MG 3 machine guns are belt-fed, using non-disintegrating metal DM1 belts, which have links that wrap around the cartridge case and are linked by a coiling wire on each side. DM1 belts are preloaded at ammunition factories in 50-round connectable belt lengths and can be linked to any length necessary. Alternatively the MG3 can also be fed by disintegrating metal M13 link belts (designated DM60 by Germany) used by many NATO member states. M13 links are also used on the Dillon M134D Minigun, M60, FN MAG, AA-52 and HK21 machine guns among others.

Both belt types use a metal lip that is arrested in the rim of the cartridges to correctly position and fix the cartridges in place. For field use there are several ammunition containers available.

The Gurttrommel (belt drum) contains a 50-round DM1 or DM60 belt. The Gurttrommel is not a true magazine but holds a curled 50-round belt preventing it from snagging, twisting and getting stuck during mobile assaults. The steel DM2 ammunition box contains a 250-round DM1 belt and the smaller plastic DM40004 ammunition box contains a 100-round DM1 belt or a 120-round DM60 belt. The German military tends to use non-disintegrating DM1 belts for general use and disintegrating DM60/M13 belts in vehicle or aircraft fixed MG3 mountings that allow for collecting the ejected link pieces for reuse.

Tripod
In a stationary, heavy machine gun role the MG 3 is mounted on a buffered Feldlafette ("field tripod") that also features storage containers for accessories like the Zielfernrohr 4 × 24 periscope-style telescopic sight. The direct fire only Zielfernrohr 4 × 24 sight like the MG 3 is mounted on the Feldlafette and is graduated from 0 to 1,600 meters (0 to 1,750 yd) in 100 meters (109 yd) increments. The Zielfernrohr 4 × 24 reticle can be illuminated by an external unit. It can also be used with the FERO-Z 51 night sight.

A unique feature of the German World War II Feldlafette types that was not carried over to the MG3 Feldlafette was the Tiefenfeuerautomat ("in-depth automatic fire"). If selected, this feature walked the fire in wave like motions up and down the range between predefined ranges. This sweeping of a given range (Tiefenfeuer - "in-depth fire") continued as long as the gun was fired.