The general "rule-of-thumb" seems to be that these Spanish Mauser .308 conversions are safe with 7.62 NATO (Military Surplus.....46,000 psi chamber pressure) ammo, but marginal with Commercial .308 Winchester (50,000+ psi chamber pressure) hunting ammo.
Here's an excellent article on this:
"Keep in mind that old rifles should be thoroughly inspected before shooting, and that each rifle is unique as to what loads it will handle. Having said that, have fun shooting your FR7 or FR8. Remember, 7.62 NATO ammo is the correct ammunition these rifles were designed to use, not the higher pressured .308 Winchester."