7.62x51 and commercial 308 operate within the same pressures (except for the "Light Magnum" line). How else could a 147 grain pill have a muzzle velocity of 2700 fps for 7.62x51 and 150 gr soft point have a muzzle velocity of 2700 fps? The laws of physics will not be denied. When you look at match ammo, M118lr and M852 they are the same as Federal GMM 175 gr and 168 gr.
The 308 Cetme round is dimensionally the same as the 7.62x51, but operates at much lower pressures. A 112 gr bullet at around 2500 fps. It is "obsolete" as Spain upgraded their current weapons to handle the Nato pressures.
Machine guns are awesome until you have to carry one.