For what its worth, I dont think you have a headspace problem. The factory ammo is usually a couple thousands short of spec and the fireformed and neck
sized should have taken care of that anyway even if the chamber were 10 thousands over. I dont think you are pulling the trigger to the side if you shoot 1/2 moa.
The unmarked primers would be my main concern. Inconsistent primer strikes can screw up your grouping, yours goes
way beyond just inconsistent. My guess would be the bolt assembly either has a short firing pin (unlikely), a weak spring, improper assembly
and adjustment or there is some foreign material in there. If you feel comfortable with disassembling the bolt, I would start there and
clean it and make sure it was put back together properly and moves smooth. If you have a strong thumb you can let the firing pin down and measure its protrusion but that wont tell you if its moving fast enough.