The MG3 fires a 7.62x51mm round. When originally made, the MG3 only supported belt-fed ammunition, and did not have a box for feeding ammunition into the weapon. However, a specially made drum has been manufactured to hold 100 rounds of linked ammunition, and this configuration is in common use. With the bipod mounted on the front of the MG3, it weighs approximately 11.05 kg.
Production of the first postwar variant of the MG 42 chambered in a standard NATO caliber (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, compared to 550 g), 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 MG 42 machine guns that remained in service were converted to chamber the standard 7.62×51mm NATO round 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. 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.