Axel can better discuss this issue.

From what I know, commercial rifles built before WW2 were for 0.318" bullets. Many Mauser rifles were had a tapered bore (first 3cm or so) so that a 0.323" bullet could be fired in the rifle without a problem. The bullet would swage down in the taper.

I have a 1937 double rifle that is 0.323" at the chamber but tapers to 0.318" in about 3 cm. The prior owner shot 8x57SR. I shoot 8x57IR as I don't want to stress the double rifle.