Damn, the shooter was real lucky.
One of my customers had a KB last fall with a Bushmaster. It turned out to be case separation. He was using commercially reloaded ammo by a major manufacture here in GA. It seems they have been using Milsurp brass for their reloads which turns out to include a lot of SAW brass.
Here are a couple pics of the aftermath. The shooter was not hurt, just scared shitless.
You can see the back of the shell casing still in the bolt.
I have a few more if anyone wants to see them too.