As the subject of things going Ka-Boom came up with that gif the other day,

this is the result of a reloading mistake

Man came in with a AR15 he'd just finished building(not his first), and a box of ammo he'd loaded to test fire it.  Came about a few minutes later with a dazed look on his face and said something like "I think I grabbed the wrong powder."  This is the upper; the lower had, I was told, a bit of a bulge on the sides but that was about it.  You could salvage the handguard, and that's about it.  The bolt, bolt carrier, upper receiver, probably the barrel extension from the look, all trashed.  

Amazingly, he was pretty much undamaged other than the shock and a couple of scratches/bruises.  Let us keep this to put in our reloading room to show people "PAY ATTENTION IS A RULE!"  In this case he grabbed a powder bottle without actually looking at the label and grabbed A1680 instead of the BLC-2 he intended, 1680 being a MUCH faster-burning propellant.