Pressure rating: The 7.62x51 SAMMI spec is 50,000 CUP or 58 000 psi max.
The 308 SAMMI spec is 62 000 psi max.
No big deal.
Chamber length or headspace:
The 7.62x51 chamber headspace spec is .005" longer than the 308 spec. This is to accommodate ammo made in many different countries in battle...