The comparably complicated construction of the MG 34 restricted mass production, therefore the numbers demanded by the wehrmacht could never be met. It was soon obvious that a simpler model was needed. 

The new machine gun was to be manufactured from pressed and punched steel parts. Three companies were requested to construct a new machinegun using sheet metal stampings. The proposed construction of the company Metall- und Lackierwarenfabrik Johannes Grossfuss AG in Döbeln looked promising from the very start. It's inventor was Dr Werner Gruner who was a specialist in the technique of punching and pressing steel. He was sent into the regular training for machine gunners in the wehrmacht to find out what a machine gun's characteristics were to be and then went on to design the MG 42. The MG 34 and the MG 42 are easily discerned even at a quick glance by their barrel housings: while the MG 34 has a round housing with many round cooling holes, the MG 42 has a square housing with oval cooling openings at the left and top side, and a large slit on the right side for barrel exchange.
The first prototype designated MG 39 was accepted for troop trials in February 1939; it was refined into the fifth and final prototype, the MG39/41, and sent into a large combat evaluation involving 1,500 MG 39/41. After small detail improvements, mass production was started and the weapon was introduced into the wehrmacht as the MG 42. Total production of the MG 42 for the German wehrmacht during WW II was 414,964. The weapon was produced by the companies Mauser AG Werke Borsigwalde, Gustloff-Werke in Suhl, Grossfuss in Döbeln, Maget in Berlin and Steyr in Vienna.
The weapon was air-cooled and recoil-operated with a short barrel recoil; the recoil mechanism based on a newly invented- construction of a breech with rollers. The belted Mauser 7.92 mm ammunition was fed from the left.
The unmatched simplicity, functionality and effectiveness of the design not only resulted in a an astonishing ruggedness and immunity to the conditions of front use, it also decreased the amount of resources and raw material necessary to produce one MG 42 to 27.5 kg; it took only 75 work hours to complete a MG 42 as opposed to the 150 necessary for the MG 34; the MG 42 cost only 250 Reichsmark. Even today it is still regarded by many experts as the best machine gun construction ever.

It had an overall length of 122.0 cm, a barrel of 53.0 cm and weighed 11.6 kg in the role as a light machine gun equipped with the bipod. The bipod, the same as on the Mg 34, could be mounted to the front or the center of the gun. In the role as a heavy machine gun it utilized the newly developed Lafette 42 ("mount") that weighed 20.5 kg. The MG42's nominal rate of fire was 1500/min; reportedly, this rate varied to a degree with individual weapons; furthermore, the rate slightly increased in prolonged bursts. The higher rate of fire led to a decreased barrel life expectancy when compared with the MG34: the barrel was only good for between 3,500 to 4,000 rounds. Later, barrels were chrome-plated which lengthened life expectancy a bit; still, the barrel became hot rather fast and had to be changed often; the MG42 accounted for this with an even further simplified barrel change mechanism.
Because of the ruggedness of the MG 42, it was preferred to issue this weapon to the infantry and rather use the MG 34 in vehicle mounts where the MG 34 was less exposed to dirt and damage.

With the acute material shortages of 1944 it was deemed necessary to further simplify to save resources. This resulted in the MG42V, also called MG 45, which modified the breech mechanism of the MG42 so that it didn't completely lock before firing. The revised locking system was a semi-rigid roller lock very similar in design to the later G3 rifles made by H&K. This increased the theoretical rate of fire even further, the weapon now only weighed 9 kg and - most importantly -production was simplified and needed only steel of minor quality. First tests were undertaken in June 1944, but development dragged on and eventually only ten were ever built.