Many years ago, when I was a IPSC/USPSA competitor and level I range officer, I saw a similar event. This one involved a Cold Gold Cup. The shooter was using reloads. The timer sounded, then "POW, POW, POW, POW, pop, STOP!, STOP!, STOP!, POW, What the..."

A squib load had enough umph to push the bullet into the barrel and cycle the slide. The next round bulged the barrel so badly that a gunsmith had to remove the barrel from the slide. Seems to me he quit match shooting after that incident.