Sorry the cam pin was not in the photo it was bent in a moon shape. I lost it somewhere before the photo. But leaving it out could cause a major problem as you stated.
The other point, one advised the rifle may have fired out of battery. I will give you a little lesson hint here. Normally when the AR or M Rifle fires out of battery the parts will have a reddish looking residue on the parts. This is caused by when the rifle fires out of battery the hot gasses since the bolt was not locked into battery cause the moisture in the air to actual cause a rusting action on the parts almost immediately. Ultra hot gasses and moisture in the air cause this. SO it will look like the bolt and various parts have like an iron ore (Reddish Brown) colored rust on it. If it has a catastrophic event (BLOW UP) with the bolt in battery at the time of the shot you will not get this rust colored residue on the parts. In this case it has none. So we confirm that the rifle was in battery when it went! So Drum ROOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO OOOOOLL!
Here is the answer to the issue!
The receiver as I advised was in 5 pieces! I will forward pics of it when I get a chance soon!
The Barrel also had signs of the pressure in the bore about 2 inches from the muzzle cased by damage occurring to the Lands and Grooves (Rifling!) Believe it or not? No visible bulge in the barrel!
The operator was rushing to do a quick clean on the rifle being back late for lunch prior to class starting. Cleaned his bore as the instructor was calling for him to get out on the line they were ready to start. As the operator ran the final cleaning patch through the bore he thought for sure he had shoved it out of the Flash Hider due to the fact a patch was laying on the floor. What actually happen the rod pulled the patch back up into the bore and from what I could determine pulled it almost all the way back to the chamber. And then the rod came out of the receiver with no patch on the tip. The further the projectile (Bullet) pushed the patch up the bore the tighter it got and the more the pressure increased. The very first shot and you know the rest of the story! Moral of the story! Never get in a hurry and assume anything. And if anything at all does not seem or sound right don't shoot it another time until you check it out. Always be absolutely shure the bore is clear.
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