I read a story somewhere that in fact the US Army was so impressed with the MG42 - difficult not to be! - that they did attempt to copy it just after the war. The problem was that the design plans were metric, and had to be converted into Imperial measurements for use by US manufacturers. However, it seems that there were some problems with the conversion, and that although a couple of guns were produced, they suffered terribly from jamming, stoppages, etc, owing to the difference in parts tolerances. Also, the 30-06 ammo used was not ideal, or something.
It may even be true - no idea!
Also, the feed system of the MG42 was combined with the gas system of the Bren gun/BAR to produce the FN MAG / L7 GPMG, which along with the MG3 is one of the most successful post-war Western machine guns.