Joe Wood and Stan are both correct about the suspicious appearance of the primers. I don't really know how the thickness and hardness of shotshell primer cups compare to rifle primers, so I don't know if valid comparisons can be made. But the sharp edge and seeming extrusion of primer cup material around the firing pin on the blown shell tell me this load, whatever it was, probably exceeded safe limits. I'd sure at least try to get my hands on all of the shells that were used from that particular box that day to measure and check for missing base wads, etc. I know that will depend on whether the shooter picked up all his empties, and what was done with them in the excitement of the aftermath. Thanks for continuing to share. You may never find the true cause, but it's important to at least try.
