I just found out the warehouse next to mine does Depot level maintenance on M16's! I spoke with the guy (I see him everyday) and got his opinion on some procedures, such as replacing barrels, etc. His 22 years of knowledge answered alot of questions for me.
I asked him to clear-up this whole "barrel replacement" battle that rages on about proper torqueing, etc. This is the method he uses:
1. He does not use a torque wrench
2. He tightens as far as he can (w/barrel wrench/bar) to line up the next notch
3. If it won't align, he lightly sands the receiver face using 1000 wet/dry on a square surface (figure 8 pattern, about 10 passes) and tries again. He repeats this until the next notch aligns. He said the sanding techique is perfectly safe, as you would have to remove an awful lot of material to mess anything up.
He also filled me in on some other techiques for doing certain things easier. He's gonna come get me the next time he does a barrel replacement. Cool!