I have made up a couple dummy rounds from 308Win. brass and .318" bullets for my Kurz and they cycle and chamber with no resistance at all.
I figure that pushing a bullet through a die to reduce it by .002" is splitting hairs so to speak since the same will be accomplished in the first inch of barrel upon firing and if there are thousands of military Mausers with .318" barrels shooting bullets a full .005" bigger than groove, there is little worry about the .002" difference in the comparatively anemic 8mm Kurz.