I had the some thing simuliar happen to me many years ago, not quite this drastic, but same effect, no more bolt carrier and upper receiver.
Pulled back the charging handle, let go. Round did not fully chamber. So use the so call forward assist, closed the chamber, pull the trigger... Kaboom...
heProblem turns out to be quite simple. The bolt did not chamber was due to the next round in the mag jammed up aginst the bolt carrier. When I used the forward assist, I just jammed it tighter. So when the round discharged, the recoil gas accumlated in the bolt carrier but because it did not move, it over pressured and found the weakest part of the bolt carrier and exit.
hing...Oh, I did rebuit the entire rifle using the same bolt, barrel, lower. Just got a new upper and bolt carrier. No problems....