Staff Writer (Updated: 6/2/2016):
The MG3 began life as the "MG1", these essentially continued production of the German wartime MG42. However, with the Western shift to the 7.62x51mm NATO standard rifle cartridge in the decade following the war, the weapon was rechambered to accept the new round, discontinuing support for the 7.92x57mm Mauser cartridge of old. To fulfill a West German Army requirement for a modern GPMG, the MG42 was selected in the new cartridge form and design work began in 1958. Several other changes were instituted to the original design to better accept and fire the NATO cartridge in full. The MG1 line was formally introduced in 1960 and, on the whole, the weapon remained faithful to the wartime MG42 - whose original manufacturing plans were lost in the conflict.
After several years of in-the-field use, engineers revisited the MG1 and added a new feed mechanism and anti-aircraft sight device with support for ammunition boxes. These changes begat the MG3 designation to which the product was formally adopted in 1968. The weapon proved a local and global success, exported to a plethora of national armies worldwide as well as entering into local production with a select few powers.
This West German machine gun has evolved along several lines of variants. MG1 was used to signify the wartime MG42 machine guns reverse engineered and rechambered by Rheinmetall to fire the 7.62x51mm NATO standard rifle cartridge. This included changes to both the feed and bolt system but the weapon retained many of the wartime version's external features and internal function including its muzzle booster and gas ports. MG1A1 (MG42/58) of 1958 featured all new calibrated sights to content with the new cartridge being fired as well as a new trigger system. The bore was also chrome lined for robustness. The MG1A2 (MG42/59) of 1959 featured a lengthened ejection port for improved extractions, a friction ring buffer and a heavier bolt assembly - the latter to contend with the weapon's high rate-of-fire - and essentially served as the prototype to the upcoming MG3. The MG1A3 was an improved MG1A2 form with a revised bolt, trigger, feed system and bipod assembly. A new muzzle booster was also added. The MG1A4 was the MG1 for vehicle-mounting and did away with the bipod assembly, anti-aircraft sighting device and shoulder strap support. A shoulder pad was added and a new muzzle booster fitted. The MG1A5 was the MG1A3 upgraded to the MG1A4 standard complete with the same muzzle booster assembly. MG2 covered the major conversion of wartime MG42s rechambered from the classic 7.92mm Mauser cartridge to the 7.62x51mm NATO round. The barrel assembly, feed mechanism and bolt system were all changed as a result.