Pierced primers

[Parashooter]

Maybe this will help -



All it take is a few minutes with some fine-grit abrasive paper or stone. Usually the pin can be nicely radiused and polished without reducing its length more than about .002". A magnifying glass helps.

As the lads are saying here, the most common cause of pierced primers is the firing pin - it's very seldom the ammunition or anything to do with headspace. When full pressure builds in the chamber, the primer cup has to stretch a bit to conform to the pin and surrounding bolt face. If the pin is rough, the cup tears instead of stretching nicely. Imagine poking a toy balloon with your elbow and then with your fingernail - same principle!