Hello Wurger,

While the two seem close they are not at all. The neck length is much shorter on the MS as well as shoulder angle and length being different. Shoulder diameter is smaller on the MS as well.

On some other odd 8mm's I use a 325wsm neck die to neck size them and use whatever appropriate seater that makes straight assembled ammo. Experience with a few MS rifles says that headspace is just an approximation to the assembler, so neck sizing only may be the way to go anyway, as to not bump the shoulder back.

CH4D has dies for it much cheaper than RCBS but they have stated a 10-12week shipping time before on 8x54KJ & 9.3x57mm dies.

As to the .318" diameter requirement, my experience with a set of Redding and RCBS 8x57JS dies is that when sizing with the expander removed the cases emerge with a .315" inside neck diameter, ready for .318" J bullets.