I used Flitz once and, while it removed the rust and put a mirror finish in my barrel, it also seemed to remove much of the bluing. I was told, later on, that there can be some residual bluing action going on and that, if I left it alone, the blue-ness would largely return. I can't say whether this is true. I was so panicked when I saw the blue had come off that I ran out and had it re-blued ASAP. Anybody know? Anyway, be careful with Flitz.