There have been "kaboom" postings before regarding the Glock which gets the most press....
As a G21 owner, I have seen these pistols tortured, yes literally tortured. and still function. The links are here in the archives. Buried, placed in buckets of sand, dirt mud, thrown from airplanes, dragged behind trucks over pavement, and still work. I was late to the "dark side" of Glock ownership, but do not believe it is a Glock issue.
History, on some posts, has shown a failure of ammo to perform. LEO's get specific ammo from specific ammo manufacturers. If there is more to this story after the follow up investigation, I'd love to read about it.
There is simply too few parts to the G21 for it to kaboom. If the round is in battery, and there is no obstruction in the barrel, it goes downrange.
It can't double feed, or cycle after a misfire, UNLESS it is done manually. Look at where the damage is. It's at the breech. Not anywhere down the barrel.
It was an ignition issue at the source, ie firing pin strikes bad round.
Just my humble .02 cents, and I still love my M+P
