Found this video, and I want to diagnose what this guy did so terribly wrong. This is what I see
-On the first click, he racks the charging handle back, does not seem to inspect the barrel for obstruction
-Then he releases the charging handle and smacks the forward assist, not quite sure what that does but I think it could jam a misfed round into the barrel
-On the other clicks he really does not check if the barrel is clear, he just racks the charging handle and then slaps the forward assist.
So I think by not checking the barrel for obstruction and slapping the forward assist, he jammed a round in the barrel and then ended up bringing another round up, and they blew up, or something like that.
-And then there is the fact that the dummy who was next to him was not wearing any eye protection. What if he was next to the gun, like he was, when it blew up, not sure though.
I'm sure I missed many points, and I'm interested to know, how did this guy f*** up so badly?