Tried assembling an upper today but just couldn't get the barrel nut to align properly to install the gas tube no matter what. Everything is greased up with Aeroshell, I tightened the nut to 30lbs three times and backed off three times before trying for final installation. The nut aligns ok at finger tight, but as soon as I torque it to 30lbs the notch has moved to far. Trying to get the next one to line up was also unsuccessful, I torqued the nut incrementally from about 32lbs right up to 80lbs, stopping every 5 to 10 lbs or so, checking at each interval for gas tube clearance and just couldn't get that next notch to move far enough along to line up either.
I spent about two hours backing the nut off, re-torquing, backing off again, re-re-torquing etc etc.. every 5-10lbs and still no go.
I have a couple other barrel nuts but the barrel in question has a fixed FSB pinned in place so unless I remove the FSB I guess I'm SOL as far as just switching nuts goes.
Are barrel nut shims my only real option at this point?
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