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Old February 26, 2012, 01:28 PM   #8
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Join Date: July 26, 2011
Location: USA
Posts: 1,619
Pierced Primer

2 kinds of pierced primers. There is a pin hole in the dead center of the primer where the pin hit. This flame cuts the firing pin nose. Primer stays in one piece. The 2nd type is where the metal of the primer thats indented breaks free on the edge of the strike. This little disc can be pushed back into the firing pin channel. This disc is pushing the pin backwards from high pressure. As most all pressure goes thru the pin channel, the bolt face may not get gas cut. This disc can bind the fining pin, causing miss fires. Or the disc can get in the action and jam the gun. Pierced or Blanked Primers.


1. Check the firing pin, it should have no gas cutting or deformities. 2. Firing pin protrusion should be checked. Internet search shows .055" to be about right for an AR15. Check with a gun smith as each firearm might be different. 3.The firing pin must stay in contact with the primer on firing. A weak hammer spring on an AR or a weak firing pin spring like on a Rem 700 bolt action will let the firing pin rebound on primer piercing when the hot gas pushes the pin backwards. 4.If the hole the pin sits in is to larger in diameter, the primer flowes back into this hole till the center of the primer separates and fall into the action or travels into the firing pin area. Bushing the firing pin hole will fix this. Or you may want to try a magnum primer with a thicker cup. Military ammo may have a crimp that needs to be removed before seating a new primer. The crimp is removed by shaving or swaging the primer pocket. Swaging may be needed here so the prime can be seated lower in the pocket. High primer = misfires & pierced primers. There is also a high pressure sign visible. The reloader was using a "starting" load and CCI 400 primers. The pressure sign may have formed on firing the factory ammo. I just shot some XM193F factory, the web area expanded .0015" on firing. This is a sigh of a "hot" load.
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