It takes a special kind of stupid to blow up a gun in this manner.
Was shooting skeet a few months back with a guy who was shooting a 12ga semi. At station 8 high he had a FTF. He waited... opened the bolt... nothing. He was totally confused. Rest of the squad was totally confused. We looked around, no shell on the ground. He was just about to load another and go, but we all yelled and made him take it down and check the barrel and sure enough he had 20ga stuck in there. And this guy was a seasoned shooter... He said he got the box of shells from a friend who was a reloader, who was loading lighter loads for him. Apparently the friend gifted him a single 20 ga shell at the bottom of the box. So bad shit can happen to good shooters... always be safe and check the barrels with any malfunction.