Pierced Primer

[Bruce_in_Oz]

Lookoing at the photo:

The case second from the left in the top row appears to have a bit of a crater "rim" around the striker mark.

This would indicate either:

Excess pressure with a "normal" primer, or

Softness of the primer cup.

Check for the fit of the striker tip where it passes through the front of the bolt head. Any more than a couple of thou' can start problems, especially with "soft" or brittle primers.

The big problem is that the gas-cutting that occurs every time a primer fails in this way will eat your bolt head and striker. The roughness that even minor gas-cutting of the striker tip causes is enough to cause subsequent primers to rupture, thus causing even more damage to the striker tip AND to the bolt head.

Strikers that are not concentric with the hole in the bolt head (particularlr through bending) will wear themselves and the striker hole eccentric. This is also "not a good thing".

The worst rifles I have seen for this problem were WW2-built Arisakas: Not too hard to fix by inserting a small, close-fitting bush in the bolt face, but still a fiddle.

Excessive striker protrusion will also work-harden and overstress the brass in the primer cup upon impact of the striker.