Lapua brass failure

[Webster]

I don't see how this was fired in a chamber with the brass "wings" all sitting to the outside of the case. Looks like an out of battery, whether it was or not, or maybe there was too much space between the front of the bolt and the back of the barrel causing a bunch of unsupported area on the brass.

On the attached image of the case head it looks like an ejector hole mark at 3:00? Remember the back about .200" of the case is never in the chamber so the extractor can grab it. Cannot imagine why it occured once without signs of damage to other cases. I would examine other cases to see if there are signs of failure. In any case I would toss all of the cases for safety reasons. Your lucky you were not injured. Are you shooting hot loads? I doubt the case was defective in some way? It was fired and reloaded an excessive number of times. It would be informitive if you had measured case head diameter on new cases and checked the diameter after maybe ever 5 or 10 firings. It failed where the case never enters the chamber for support.