An easy way to check which bullet the rifle is chambered for is to try to push an S diameter (.323")
into the mouth of a fired case. It shouldn't fit, if the bore is .318". I have two drillings, one a pre-war Sauer and the other a pre-war Greifelt, the first in 8X57 JR and the other in 8X60R. Both use the .318" bullet and neither will accept an S bullet in the fired case. Both have the caliber markings on the rib, so there is no question which bullet they use.