Loose primer pocket. The load is pushing the primer out.
Solutions:
Check press set-up. Reseat primer.
Increase shotshell crimp length
Disassemble and discard the hull.
Place in a misfit bag. Shoot, then discard hull.
These writings and website contain my recollections, opinions, and things I’ve done in the past that have been successful for me. They might not work for you! REMEMBER YOU ARE RESPONSIBLE FOR YOUR ACTIONS!