I'll defer to others more experienced. That said I have seen almost the exact same situation with one of my double rifles. I own a circa 1911 JP Sauer double rifle, chambered in 9.3x74r. I don't have the primer problem that you do, but the case dimensions are very similar, including the banding around the case head.
I believe the rifle was originally chambered to 9.3x72 sauer and then reamed out (in Germany) to 9.3x74R. When you fire 9.3x74r ammunition you are effectively fire forming the case and the base of the case expands to fit the original 9.3x72 dimensions (the base of the 72 sauer case is larger than the 74R case). In my rifle, the bullets from all factory ammo cross (Hornady, S&B, norma, RWS, etc). I believe the original 9.3x72 load was probably a 194 or 232 grain bullet with a lower velocity. If I take fired cases from my rifle, they won't fit a standard 9.3x74r chamber as the base of the case is too fat.
My suggestion would be to use a lighter bullet at a lower velocity, then work back to the 286 grain bullets. It is taken me a fair amount of time and money to understand all this, but that is part of the fun. Hope this helps.
