man, the israelis converted german made 98 mausers just like yours to 7.62x51mm so i guess i dont understand why you cant shoot surplus out of it?
another thing ive always heard was that surplus 7.62x51mm firearms were proofed to 50,000 C.U.P. (which i believe is the same as 8mm mauser)
where .308 winchester is proofed to the SAAMI spec of 62000 psi
ive always thought .308 winchester commercial ammo was loaded higher than 762 nato
8mm on the other hand is the opposite. ive always heard commercial loadings in 8mm were less than surplus because the US manufacturers were concerned there ammo would be shot out of a reduced diameter early bore used on the early mauser rifles
certainly no expert, just curious why your gunsmith feels that way