"...knurled nut is stuck on the gun..." Tube is loose, but the locking ring isn't? Right. That isn't good. Might be rusted in. Penetrating oil.
Try putting a rubber band on it. Wrap it a couple of times. Gives you a better grip. Just like getting a jar lid off.
Try putting a rubber band on it. Wrap it a couple of times. Gives you a better grip. Just like getting a jar lid off.
