Pierced primers on factory ammo??!?!

[Dave M.]

So I went to work up a new load when I changed over guns the other day,
I changed scope between guns too so I had to dial gun in close again before I could work up an accuracy load. I had 6 Hornady 60gn TAP bullets left (223)
That I thought I’d use to get it close on paper before I started working the load up. I punctured 4 of the 6 primers!. I had to work load up anyway as I needed gun for work that night and barrel is shot on other gun. Worked up a hot but accurate fireforming load of federal primers 27.4gn ADI 8208 with 52gn Speer HP halfway up neck and no pressure signs or blown primer. Have had 300+ rounds through since and not a problem….. any thoughts?? How can a factory round do that?

Might need to get the firing pin bushed as well.

 

[Old Navy]

It has been my experience that, in an overload work up, the 223 case head will fail before the primer would pierce. As a result, I have almost never seen a 223 primer pierce.

Same for the weaker belted magnum case heads.
Same for even weaker Mauser case heads [270 or 250sav]

But the 6mmBR case head with small primer pocket and Mauser outside dimensions is stronger than the primers. On one hunting trip, I had to disassemble a 6mmBR Rem 700 bolt, and remove many primer divots that were jamming up the bolt.

What does it all mean?
I would suspect the rifle's firing pin or firing pin hole.

Never saw cases separate below the head like those. Only one I have seen that go vertical were extremely corroded. Got you money's worth out of those.