First off, I can't believe that anyone would risk their lives or eye sight firing ammo that had already shown to be a serious problem.
Second, sounds like a high pressure problem blowing the primers or spliting the cases. The particles you were being hit by would be coming out of the bolt area. This should have ruined the extractor, ejector, locked up the bolt and left part of the case in the chamber.
Contact Rem as soon as possible to let them know there is a problem before it happens to someone else.
