The Germans made three tapper bore anti-tank guns in WWII. The bores tappered from 28mm-20mm, 40.3mm-29.4mm and 75mm-58mm and all had muzzle velocities in excess of 4,000 fps. There difficult to manufacture, and saw limited use to the shortage of tungsten. Even after the German military switched to the 8x57JS (.323"), many commercial rifles continued to be made in the original 8x57J (.318") caliber. So unless marked "S" or "JS". it's a good idea to slug the bore of any pre WWII German 8mm sporing rifles, rimmed or rimless.
