This thread really has taken on a life of it's own!!! I never thought it would create so much intrest when I started it. As for blown primers and such, for the most part it is a thing of the past with modern components and the pressures involved in double rifles. Modern large rifle and large rifle magnum primers are designed to take over well over 70,000 psi. This is far beyond any sane loading and the only cartridges loaded this hot are some of the Lazeroni stuff. The firing pin diameter should be around .074" plus or minus .004" and protrusion no more then.064" pluss or minus .002" for a modern high intensity cartridge. so with a double we have a little bit more leway as to diameter but not much. As important if not more so then diameter is how well the pin fits the hole in the face. Thi firing pins should be as close fitting as possably as this in it self limits the chances for flow back of the primer and blown primers.
By the way nice pictures guys and thanks for your input and the checkering on my .450 # 2 N.E. is about half done and I will have pictures soon.