7.62NATO

What normally happens is carbon will build up either on the under side if the fireing pin or in the cup it self that does not allow the pin to fully extend out of the cup.



Look at the picture of the firing pin near #3... carbon can collect on the < (angled) surface of the pin and in the cup where the angled surface contacts the cup in the firing pin hole. This can also cause the pin to be sticky - not want to return.