Ha! Funny you should mention this. I brought up what you've described (S.E.E.: Secondary Explosive Effect) in a thread on another forum recently as a point of discussion only, not proof of a incident being discussed there, and was chastised for bringing up an "old wives tale"; a phenomenon often repeated but never proven (for the record, it does NOT appear that it's ever been proven under laboratory conditions) Like I said on that forum, I've been around long enough to know to "never say never". Without knowing all the specifics of our OP's particular load, I think it's a bit premature to say that's what happened. Personally, I think you would still see some kind of evidence that the primer was struck by the firing pin.