This note is specific to the M1a platform only:
.308win and 7.62x51 are interchangeable on the M1a platform, with the following caveat-
Keep the bullet weight below 180gr.
Heavier bullets, unless you have modified the gas system of the rifle to accommodate them, can bend the operating rod on the M1a. In extreme cases, the operating rod can hit the receiver hard enough to crack it.
The issue is not that the .308win commercial loads are loaded hotter, or that .308 is rated at a higher pressure than 7.62x51 (read elsewhere for a discussion of that issue). The issue is that the heavier bullets, though well within spec for chamber pressure create excess pressure at the gas port of the semi-automatic M1a. The excess pressure pushes the piston much harder with resultant effects further down the chain of the semi-automatic action.
It should also be noted that, when reloading for the M1a, one should keep to the range of powders specifically recommended for the M1a. A powder that burns too slowly may create a lower chamber pressure than a faster powder, but can create excess port pressure as a result of the slower combustion.