I finally got around to finishing my upper a few weeks ago and just noticed that the top rails on the upper and rail are off, by literally a hair. But enough to annoy me that I didn’t catch it when I was assembling it.

Question is, with that two piece nut, how much does it need to be loosened to turn the barrel nut just a shade? I know the inner nut locks the rail to the barrel nut, but I’m afraid to heave on the barrel nut with the inner one ran in, unless that can be confirmed to be ok. I hate having to back it off, but I don’t think it’s avoidable.