I just tried to use a pipe wrench to remove a barrel from a 10 p-sr 308. I got it loose, brushed clean the threads and proceeded to remove the nut part of the way, which is where it got stuck and would not move. I tried to back it off. I oiled the threads more. Long story short, I had to dremel it off. After the nut was removed, I noticed that the threads were completely packed with bluing salts (?) and small pieces of "grit".