I have had problems with split necks and cured it by annealing with molten lead, just 3 seconds immersed up to the shoulder, (no more). Then water quench. Keep the water and any potential splashes well away from the lead and wear PPE like safety glasses. Make sure the primer pocket is blocked with a spent primer or a drop of lead will go into the case and be very hard to remove. You might find that lead does a better job than a flame or restoring cases.

I do have a 9,5x57 M-Sch. I use 9,3x57 Norma cases and one pass in a RCBS FL 9,5x57 M.Sch. die. But I have also converted .30-06. Head space issues can be cured by oversizing the necks, then set the case into a well backed off 9,5x57 die and slowly turn it down until the bolt will close on the case with just light resistance. CH4D tapered expanders do a good job of expanding the neck. If you smoke the neck, you'll be able to more easily see the progress of the neck being sized.

I had a headspace problem with 8x56 M.Sch. The primer would back out half way. Once the neck was oversized, then re-set as above, the primers stayed where they belong.

Only cases with the right headstamp I know are Kynoch Berdan primed. I have reloaded 6,5x54 M. Sch. with Berdans. No real problems except the primer source has since dried up here. But velocity and accuracy were the same as Boxer.

One thought is that, I use a Hornady case concentricity tool. This straightens up the bullets. But it also means the case will, IMHO, form straighter. It makes any load more accurate too.