The US Army tried to copy the MG42 during the war. The experimental copy was called the T24 machine gun. This wasn't an exact copy, since it was chambered for the .30-06 Springfield cartridge instead of the German 7.92×57mm Mauser cartridge. It also used a heavier bolt, deliberately chosen to slow the rate of fire. The T24 was tested in 1944, and abandoned because it was too defective - it was very prone to jamming. The abandonment resulted from realising that the .30-06 Springfield cartridge was too long for the original ejection mechanism, and significant redesign was needed, and even if it worked, the new MG wouldn't be ready for use during the war.

This wasn't the end of the US Army's work with the MG42 design - it was a major influence on the M60 machine gun, introduced in 1957. The Belgian FN MAG, introduced in 1958, also used elements from the MG42 design. Since both the M60 and FM MAG were widely used, these part-derivatives of the MG42 design are relatively well-known.

The Swiss got into the game of copying the MG42 very early, in 1942. The result was the MG51, essentially an improved MG42 chambered for the 7.5×55mm Swiss cartridge, which replaced many stamped parts with machined parts. The resulting gun was heavier than the MG42, and more reliable - both of these resulting from switching from stamped to machined (other design elements also contributed to the extra 4kg of weight compared to the MG42). This wasn't the end of the Swiss MG42 adventure. In 1955, a few years after the Swiss Army adopted the MG51 (in 1951), SIG (Schweizerische Industrie Gesellschaft) began work on another MG42-derived gun for the export market. This was prototyped for a variety of cartridges, such as 6.5×55mm, 7.92×57mm Mauser cartridge, and the standard NATO 7.62×51mm cartridge. It was the last of these (7.62x51mm) which went into production as the SIG MG 710-3.

West Germany also reverse-engineered the MG42. The original blueprints and drawings had gone east as Soviet war loot, and reverse-engineering was necessary. The result was the MG1, essentially a clone of the original MG42 chambered for the NATO 7.62x51mm cartridge. This gun went into production in 1958, and then almost immediately spawned a variety of improved versions (such as the MG1A1 with a chrome-lined barrel and sights designed for the new cartridge, and the MG1A2 and MG1A3 with further improvements). Ex-WWII MG42s were converted to fire the NATO cartridge, and were designated MG2. In 1968, the further-improved MG3 was introduced, and in addition to new production, existing MG1 and MG2 guns were upgraded to the MG3 standard. The MG3 was still at heart a rechambered MG42, and was compatible with many original MG42 parts.

Austria also used ex-war MG42s rechambered for NATO 7.62x51mm. These re-chambered guns were adopted by the Austrian Army in 1959, and a program to develop a similar Austrian-made gun immediately begun. The development appears to have been rather leisurely, being finally completed in 1974 as the MG74. The new gun was based on the MG42, and also the new West German versions (the MG1, MG2, and MG3). One design goal for the MG74 was to reduced the rate of fire.

Finally, we can note the Yugoslavian M53, which retained the 7.92×57mm Mauser cartridge, and was made using much of the original wartime machinery used to make the MG42. Unsurprisingly, there were few differences from the wartime MG42 (the rate of fire was reduced to 950 rounds per minute, which is still high even if slower than the MG42).

The German MG1/2/3 were notable in retaining the MG42's high rate of fire. Many of the other derivatives (such as the US T24 attempt) deliberately lowered the rate of fire - reducing ammunition usage was seen a more useful than such a high rate of fire, with the exception of anti-aircraft usage (where rifle-calibre machine guns were not particularly effective anyway). Thus, a feature that many consider one of the strong points of the MG42 design was not seen as useful by many potential users (with the notable exception of the Bundeswehr). Another feature of the MG42, cheap manufacture through use of stamped parts, was also abandoned by some of the derivative guns (e.g., the Swiss MG51).