Primers Backing Out

[Hammerforged]

If it was my gun I would check the head spacing to be sure, then work up loads that are higher pressure. I have never had a backing out problem with high pressure, moderate to heavy loads in any cartridge. I have had only one instance where the primers were backing out. This was with Remington factory loaded ammunition in .257 Roberts. We all know that they try to keep pressures low in this cartridge for the old small ring designs of Mauser rifles.

Are you getting any blow-by (soot around the case)?