Assuming this ammo was properly loaded (??) it could have been fired in a gun that had a headspace problem.
However I would guess that it was a little "warm" loaded.
Was it hard to resize . . . like the brass was bigger than SAAMI specs. A short chamber could also cause this.
See if you can find the history of the brass for a "good to know" sorta thing. However . . . if some of the pockets are too loose,it's still gotta go.
Check the brass that WILL take a primer to see if it will properly seat in the pocket also. I know a guy that was gettin' ready to load 100pcs of 50Beowulf brass. He used a primer pocket uniformed that was "just a little" too big. OUCH !! ---- SAWMAN