NATO 7.62 cup pressure converts to about 58,000 psi, based on some charts that somebody linked elsewhere.
Commercial .308 seems to average a max. psi of about 62,000. The test pressures for both are much higher.
As for old Spanish (early 1900s) converted from 7mm to NATO .308, some middle-aged gun show buddies who are very familiar with Mausers are really skeptical about the strength of the Spanish steel from 1916 or so.
I learned about this when a seller at a gun show nearby in Southaven had such a converted Mauser. I asked him about the issue and either he was unfamiliar, or pretended not to be aware. That seller is no young guy either
....An acquaintance who stood at a table behind him looked at me and slowly shook his head, then confirmed my concerns.
The other fact that so many people confuse the Spanish FR7, built on very old 7mm actions, with the FR8, built on the much later, stronger 8mm actions made the search for info on the safety of my FR8's digestion of commercial .308 even more time-consuming.
By the way, even though some FR8s etc can fail the headspace check using a Go/No Go gauge, the Win. .308 field gauge results in my rifle are excellent, and the (SAAMI) gauge is very cheap: with shipping $30, Brownell's, 800-741 0015.