I would like to know if 8x56 MS cases can be formed from 8x57 (rimless) brass? If so, is it just a matter of trimming the 8x57 cases to length and then running them through a 8x56 MS sizing die?
Thank you in advance for any help.

I don't know teh exsact presidure, but I know it can be done!

I friend of mine got a nice old mannlicher chamberes for 8X56Ms, he was just about to rechamber to 8x57is, when we stopped him!

Well he bought a die for 8x56 ms, and now he shots it we 8X57 cases - my best guess is that he just runs them through teh die and trim tehm a little - as you self surgetsted!

Regards

Mads

I believe the procedure is to lube it well, run it through the 8X56mm MS full-length die, then trim to the trim-to length for the 8X56mm case. (2.20") It appears to require very little change to make the 8x57 Mauser case into the 8X6mm MS. There is a little loading data in Cartridges of the World. According to COTW, the MS case has a base dia. of .465", while the 8X57 is .470". Case lengths are 2.21" vs 2.24", and shoulder diameters are .424" for the MS and .435" for the 8X57 Mauser. According to COTW, the MS round is loaded to about .35 Rem. ballistics. With the cases so close in capacity, I don't see why it would be necessary to limit the power so much in a good strong action. I don't know how strong the early MS actions are, but the recent ones were chambered for the .270, .308, .358, and other high-intensity rounds. The action design is the same, but later metallurgy may be better.

Thank you both for the information!