I saw test results of a German small arms test in 1991 very recently (not for the first time).
It compared G3 (~M14) and AK-74. The latter (high quality Eastern German licensed copies that were later sold to Turkey) proved to be superior up to 200m, with G3 having advantages beyond that distance in great part thanks to its longer sight line (now irrelevant with standard optics).

The M14 was most likely never even close to an optimum compromise. The magazine capacity is low, recoil is strong, it's heavy, long and the cartridges are heavy & bulky as well.

Almost a hundred years of optimum cartridge finding projects have almost always yielded an optimum cartridge of 6-7 mm calibre for an (assault) rifle, with few exceptions during the 30's and 40's when assault rifle(-like) designs were seen as relatives of submachine guns and rifle-like range not required. Those optimum compromises looked similar to 7.62mmx39.

We would discuss the disadvantages of the M14 and the screwed up 7.62x51 nonsense that was a poor cartridge from the start if there had not been the AR-15 and 5.56mmx45.


Let's get over the loss of M14 and G3 and accept that the next step should be an intermediate bullet (with whatever cartridge design - there's still the telescoped stuff around, after all).

By the way, PEO soldier has launched a new carbine competition without requiring a specific calibre.