Naw, you can see powder exit the barrel when that second to last round is fired.looks like she had a squib, and then racked a new shell in and it went boom.
I am the person this happened to. The 7th round jammed, which is nothing unusual for this gun. It happens all the time. That is why I didn't really hesitate to shoot the final round. We were using newer ammo, so we don't think that's the problem. My brother has been looking at his M1, and we noticed it will still fire with the chamber not fully closed. The chamber can be open up to 1/2" and the weapon will still fire. We think that's what happend.