Call Brownell's and talk to one of their technicians, they can point you toward several options. I've used Oxpho blue for several guns, but on some steels the color will fade to brown after about a year. I had a beautiful dark blue on a Stevens Ideal rebarrel--it was brown a year later; same with a Mossberg 44. I know some people use a rust blue process that you apply, card with steel wool, repeat, then finally "set" by boiling in distilled water or by steaming in a box. Relatively inexpensive (though more so than Oxpho) but gives a superb finish. I know a guy who's done this for a Browning A5 and Remington Rolling Block with excellent results.