UIncle buck, pierced primers, there is the .7854 principal.
Pierced primers, a weak firing pin spring can guarantee a pierced primer, not a balancing act but the pressure on the firing pin must be greater than the pressure inside the primer/case. When the pressure is greater inside the case/primer the pressure pushes the firing pin back, when the firing pin is pushed back ‘far enough?’ the dent in the primer becomes a hole, and that is when the hot, high pressure, metal cutting gas cuts the face of the bolt around the firing pin hole.
And that is where the crater term comes from, the primer becomes a mirror of the bolt face, firing pin and hole around the firing pin, when a creater appers, descriped as a dent with a high ridge around it damage has been done.
Normally, the firing pin crushed the primer with a big dent, then the pressure inside the primer forces the primer to conform to the firing pin, again, if the firing pin spring can not exert enough pressure on the firing pin the firing pin moves back. Then there is the nail effect, the nail does not make a good firing pin, the firing pin is designed to crush the primer, I have rifles that have firing pins that are not bashful about crushing primers.
Last edited by F. Guffey; February 26, 2012 at 12:23 PM.
Reason: remove an 'I'