Greetings gentlemen
Blue Wonder is nice for small scratches here and there. I use this stuff on my hunting rifles/shotguns. The biggest area I have 'blued' is where the rear sight on a Mauser K98 barrel normaly would be attached. Compared to the rest of the barrel, it tend to rust more easily and is somewhat less durable. Touching up a Luger with this would be a big no-no in my eyes btw.
John; thanks, your link was interesting reading