Brownells sells a product called Oxpho-Blue. I've had great results with it. I've found, the hard way, that your success is directly related to the quality of metal prep you do before bluing the piece. If you take short cuts, you'll get an inconsistent but blued surface.
Not being an expert I use the Blue-Wonder (also a decent product if you do the prep and have a heat gun) metal prep instructions and try to be extremely thorough. I've developed a particular fondness for their gun cleaner.
Oxpho-Blue also does not omit the foul rusty smell that some other cold bluing liquids do. I've had zero rust issues after over a year.
If I have the presence of mind tomorrow I will take some pictures of a couple guns I have done.