Re: DPMS 260 issues?
How does the mouth of the case look?
Can you see rifling on the front edge?
I could see where over pressure would extrude material into the ejector, but not smearing it!
The case is being held in place as the bolt head is rotating!
I know nothing about your rifle, but it would seem to be a lockup issue, the case is jammed into the rifling, or a timing issue!
I'll be interested in what the cause is.