Someone I knew had a old Harrison and Hussey rifle in 8x57 Mauser that had headspace issues when he acquired it. His gunsmith turned the barrel down and rotated it about 3/4 (?) turn and that made it into an 8x56 M.-Sch. It worked fine. Years later his widow asked me to sell it. I sold it to a collector who rotated it back, corrected the headspace and now it's an 8x57 again. It was originally blued after the sights were fitted, so it meant the bare patches were all covered up again.

I seem to recall that Walter also had a small amount removed from the 8x57 Mauser FL sizing die - or it might have been from the shell-holder. I spoke to a gunsmith about it and he thought that one of those options was better than the other but I can't recall which option or why. Perhaps, a modified shellholder would allow the owner to still reload both calibers.

A look at the cartridge drawings, (both are available online), of the two would show if the shoulder angles, body taper and etc are the same or similar enough and you should be able to determine the difference required in die length. I shoot an 8x56 M.Sch. but use RCBS dies in that caliber. However someone converted me to using Hornady in-line seating dies so I now use an 8x57 Mauser one for both 8x56 M.-Sch. and 8x57JR. The latter uses smaller diameter .318" bullets, but the seater die works just fine.