jonnyc, consider the following when thinking about the 7.62 NATO and .308 Win. development history:
oneoldsap, lots of folks get steller accuracy shooting 7.62 NATO ammo in their .308 Win. chambered rifles. Especially those competing in the Palma matches in the '60's and '70's at Camp Perry shooting Winchester 70 match rifles with Lake City 7.62 NATO match ammo. And around the world, other countries have been shooting their arsenal NATO ammo in .308 Win. chambered match rifles in fullbore competition for decades; good lots of it would shoot near MOA at 1000 yards.
But it's the bore and groove dimensions being correct for bullet diameters that make it work. Winchester's barrels in their Palma rifles had .3083" or thereabouts groove diameters. The .3086" diameter 172-gr. FMJBT match bullets in M118 7.62 match ammo did great. Overseas, arsenals' bullets were typically .3075" in diameter so the Brits and their Commonwealth buddies used .308 Win. chambered barrels with .3065" to .3070" groove diameters to shoot their 147-gr. bullets very accurate.
Whenever bullet diameters are smaller than groove diameters, stellar accuracy is about impossible. By stellar accuracy for arsenal ammo, I mean 1/3 MOA at 100 yards, 2/3 MOA at 600 yards and 1 MOA at 1000.
For those quoting peak pressure differences, note the US arsenals in the early 1950's set the max average pressure for the NATO version at 50,000 cup. Winchester set the commercial version at 52,000 cup max average pressure in 1952. So, all things being equal, does this mean the commercial versions were unsafe in the M14?