It sounds to me like it's copper, not rust. I just bought a used gun and the barrel had alot of copper in the grooves at first I thought it might have been rust,and I used Gunslick's foaming bore cleaner in it. It was ALL copper, the first patch I ran through it was a very deep blue color. I use rem oil in my barrels without any problems of rust.
Last edited by sako4me; 08/27/08.
