My experience
I bought an 8mm Spanish Mauser (1943 model, made in 1951) a while back. It had 7.9 stamped on the barrel (i.e. 7.92X57). However, when a lot of these were sporterized they were bored to something like 30.06. What I did was asked my gunsmith to do a chamber cast to assure that the rifle was an 8mm Mauser (7.92X57) with a .323 bore. (Some really old Mausers had a .318 bore, all made before 1905, but if yours does not have the original barrel, who knows). Once it was verified, I started shooting it. It ended up being a great rifle and including the chamber cast, cost me $100.
I should also mention that mine has R202 on the bolt, receiver, floor plate and barrel and I think this is its serial number. They all matched.