Quoted:
I just got a DD lite rail and went to install it on one of my rifles. The rifle that I am working on had a complete upper assembly from CMMG. I understand that the barrel nut should be torqued between 50-80 ft lbs, (which always seems insanely light to me, and I worry about the barrel nut becoming loose, but I stick by it).
Anyway... The barrel was torqued down so much that I almost had to use a cheater bar to break it free. I'm guessing the person that assembled it couldn't get the barrel nut to index properly for the gas tube.
What is the worst case scenario for over torquing a barrel? Can you tighten it so much that it affects headspacing? Damage to the receiver?
Having trouble loosening the barrel nut does not necessarily indicate that it was overtorqued. It could be that the grease used on the barrel nut had dried out over time. Remember, one major purpose of that grease is "anti-seize." That it took three men and a stout boy to break that nut loose just means that it was stuck, not over torqued.
Worst case: your upper could be toast. Headspace is set by the barrel extension, and there's no way you can affect that with the barrel nut.