I wish the OP would tell us more about the reloads he was shooting & add some pictures of the spent shell cases including the primers and type of primer used. I suspect this break was caused by chamber gases building up in the stock in letting cavity most likely caused by a pierced primer.

I have recently experienced pierced Cheddite primers with two different loads in two different gauges with the most recent just yesterday shooting sporting clays. In both cases I was shooting almost new O/U target guns & didn't have any damage other than some light pitting on the firing pin nose caused by the hot gases escaping from the pierced hole in the primer. On the first gun I experienced this; I was able to pull the firing pin and polish out the defect. I then changed over to Winchester 209 primers in the same load and have not had a pierced primer since in the same gun, with the same loading, just different primers.

After yesterday's experience I had to do the same thing to the nose of the firing pin on this gun and will be changing that loading over to W-209 primers as well. This seems to be a fairly common issue with cheddite primers in some guns. When I was trying to figure out what was going on with the first gun, I went to the shotgun world website and did a search for pierced primers and found several threads with dozens of posts about pierced Cheddite primers. Most of these had a commonality of being shot in a wide range of different manufacture's guns but most were O/U's having this occur on the bottom barrel, which has been my experience as well.

The head scratcher for me has been. Why the inconsistency in having this happen? Between me & my buddies, we've shot thousands of cheddite primers and I'm the only one who's experienced this and then not on every round when this has happened. Even yesterday when this was happening in my 20ga, it was probably only on maybe seven out of one hundred rounds shot and it occurred in both barrels, not just the bottom like I experienced in my 12ga. All I know is its W-209 primers from now on going forward. Now I'll see if it's the gun or the primers being the culprit.

Last edited by dogon; 10/09/25 09:53 AM.