The only full-auto M16 I had was in basic. The lower receiver was marked "Colt AR-15" and had been modified to the M16A1 configuration. You could see daylight between the upper and lower receivers, and it rattled if you shook it. I still managed to shoot expert with it though. We never got to fire full auto in basic though.That looks like he's shooting full auto. If so,, that's an EXPENSIVE firearm to destroy.
When I was in the army, and at a range,, where they wanted to shoot up the ammo that had been checked out for practice & training,, they asked us to "burn some up. Well, I was doing something similar,, but I was trying to see how fast I could engage targets on full auto, keep it on target & do so with the "spray & pray" attitude that some thought was a good idea.
But when the forend got too hot to touch, and the barrel got a bit discolored,, I stopped using that M16, and got another one.
According to the armorer,, I ruined (2) M16 barrels that day. I never went that far and even beck then, I would not have been stupid enough to keep shooting if it was on fire or melting parts.