Well, I rounded out the firing pin and added a floor spacer to the bottom of the cup around the firing pin. I used a .30 cal carbine head as the spacer. after some tweeking, this left about .030 of the pin exposed. The primers with no charge detonated and fell right out after opening the bolt. The charged loads functioned well too but as before, the back presure was blowing the primer loose from the cup. However, the floor spacer was doing its job, holding the primer from blowing back around the firing pin.
Looks like I can get some follow up shots now.
Frog, could you tell me some of the problems you had with your 700?