A customer got a Mosin Nagant and surplus ammo (7.62x54R) He sent me an email and said:

The surplus ammo works perfectly in the rifle. My son wants to use the rifle this fall for deer, so we purchased some Winchester deer rounds for it. The primers on the original ammo are set slightly below the surface of the brass, while the Winchester's primers are flush with the end of the shell, which is causing the firing pin to pierce the primer casing altogether. While this hasn't seemed to hurt the firing pin or bolt (yet, after using half a box of ammo), the little pieces of brass from the primer are getting blown back into the bolt and jamming the pin mechanism, which 1) must be bad, and 2) is inconvenient since the bolt must be disassembled to unjam.

I told him the surplus ammo probably has a pretty hard cup and the firing pin spring is probably very strong to make sure, in a war time scenario the rounds are reliably ignited. I said the Winchester primer cups, as compared to the surplus ammo primer cups are probably quite a bit softer, thus the strong firing pin spring is piercing them. I told him he could try other none surplus ammo to see what happens, possibly find a firing pin spring that is just a bit weaker or just use the surplus ammo to hunt with (have to check what the bullet make up is and what the game laws say).

Any other ideas, remarks, suggestions. Both he and the son like the Mosin and according to him it is very accurate.