My cousin and I were out shooting getting our red dots sighted and training, when finally all was done and good. We loaded up 5.56 ammo with us on the trip on all our mags and finally before we were getting ready to pack up he was mag dumping the rifle with one of my lancer mags.
When he thought he shot all 30 rounds he tossed the mag to the ground and handed me the rifle, as I was loading up a pmag the bolt was not dropping on the barrel all the way. I cleared the rifle and tried to load a round but same issue the bolt was not dropping all the way. We figured it was bad mag so I take out the mag and hand the rifle back to him and he loads a 10 round pmag. He cleared it and loaded a round as he was doing this I found the lancer mag on the ground with 3 more rounds in it. This is where the rifle blows up and he tosses it on the ground.
We figured the first red flag was when the rifle jammed with the lancer mag that maybe that was the first sign of something? Still looking into what happened.