I stepped up to a .300 WSM for elk, moose and other large game animals ! I used my reloads with 180 accubonds and have one shot kills on several moose and a bull elk !
I think that you're seating too close to the lands for a hunting load ! I would measure your family story round ,load a few rounds with your receipe and try them ! If results are good I would back off to 020 to .050 from the lands !
I had the same problem when I bumped the shoulder too much ! Complete separation due to incorrect headspace! You only need to bump the thickness of a dollar bill !