A buddy of mine came by tonight with a new upper receiver that he wanted to reconfigure. It was from a reputable manufacturer and originally came with an FSB, standard barrel nut etc. My friend wanted to remove the FSB, install a low profile gas block and a Troy rail. Simple, right?
Well, the FSB comes off, no problem. I then ran into serious trouble with the barrel nut. Using a cheater bar, I was initially unable to move it at all. Finally, it moved slightly and then stopped dead. We worked on it for almost an hour, taking our time and being very careful trying not to damage anything. Right before I gave up, I decided to try and torque it back down to see if we could get the nut moving. Applying torque clockwise, the nut moved slightly. I then reversed the torque counterclockwise and it finally loosened. It was tightened well beyond 80 ft lbs and required a tremendous amount of torque to loosen.
As you can imagine, the upper was slightly damaged. By slightly, I mean that the notch was slightly wallowed out. No cracking or visible shearing, just very slightly widened. Upon reassembly, the barrel was shifting as the barrel nut was torqued on. It looked Ok, with the feed ramps only slightly off center. It was able to shift due to the now widened notch in the upper.
Everything looked fine until I dropped a BCG into the upper. We tried three in all, 2 BCM's and a WMD bcg. The WMD would not go into battery. One BCM closed easily and the second BCM closed with a little resistance. The lugs of the the WMD bcg were slightly larger than the BCM's and were contacting the extension. It was unable to go into battery because the extension / barrel were turned slightly in the upper. The combination of slightly larger bolt lugs (measured at 0.103) and the tilted extension would not allow the bolt to go into battery. The WMD bolt worked fine before disassembly.
So, I have two questions:
1) How can one remove an overly tight barrel nut without damaging the receiver? Or is it sometimes unavoidable?
2) Should the upper be replaced under warranty due to the barrel nut being installed with more than 80 ft lbs of torque and causing unavoidable damage in order to remove it?


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