I have been reloading for 10 years of and on when I need. Over time I have amassed a few rounds that have not fired. I have tried to fire them twice. The firing pin has put a nice dent in the primer. I cant say I have a bad batch of primers as it has happened when I use different manufacturers. I think I am causing it by the seating depth. I may not be verifying the depth is not consistent. As any Reloader knows the primer consists of a cup, flammable material and a 3 pronged metal piece. My question is when the primer is seated does the cups lip surface touch the bottom of the casings primer pocket or does the edges of 3 pronged metal piece? I tend to believe the 3 pronged metal piece does so it is stationary. This way when the pin strikes the face of the cup the cups inner surface forms a bulge that smashes the flammable material between it and the 3 pronged metal piece. If this is the case then should I set the cup depth on the casing to the thickness between the primer cup face to the edges of the 3 pronged metal piece?