3.5% nickel rod from Brownell's rust blues well and you can keep the original looking polish. It flows nice and works easy. Go slow - I've welded some screw holes in rifle actions that took me as many as 5 sit-downs to fill. Basically just get it hot enough to melt the parent mat'l and rod. Add a little rod and quit before the surrounding area gets hot. This keeps the heat affected zone much smaller, which is what you want. If you really pour the heat to it you can wind up warping all kinds of things that need to stay straight!
