I’ve seen some close up photos during the incident. It looks to me as if the pumpkin was jammed in the barrel & it was a forced chamber explosion. All that air volume & pressure had to go some where & it found the weakest point in the breech.
I was there. This is a good description of what happened. Breach Failure, it was bad. She basically stepped into the shrapnel, and will surely be the last event in DE. Person was a correspondent for the Science Channel.