RE: Need some info
get a (Hornady) manual and follow it to the "T"
My Hornady manual calls for a .323 bullet for the 8X57S
The bullet diameter was changed from .318 in 1905
A good dial or digital calipers will be sufficient to measure the barrel.....but if there's info as to the date of Mfg you can use .323 bullets if the gun was made after 1905...BUT MEASURE THE BARREL
Personally I've never seen a pre 1905 M-98 mauser.