I have a Strover sporter '98 in 8 X 57 with the .318 bore and my to date, limited experience has been with a 200 gr. cast & gas checked bullet. The only sizing die I have that is close is .321. The sized bullet fits into the case mouth but just barely. It's loose enough I don't believe it's causing any pressure problems but I wouldn't want it any tighter. Anyway, the first load I tried was 30 grs. of H-4895 from the Lyman cast bullet book. That load was listed for the '98 Mauser and Lyman called it out for the .323 bore but as pressures were listed and pretty mild I wasn't concerned with it. At 50 yards, benched they just about all went into one hole. Given that .321 is obviously close to the throat dimension that could be the reason it shot so good. Another reason for the accuracy is no doubt the Lyman aperture sight that was installed sometime in the distant past.

As others have said, slug your bore and throat, then you aren't guessing. If the bore is decent you should be able to make it shoot.