I find that browning works best on blasted finishes, so no worries. I use the Birchwood Casey stuff, and it seems to work fine. I heat the parts over a propane stove if they're small and my bluing tank burner if big like a barrel. I paint the solution on as fast as I can with a wool dauber, then card it off under running water with steel wool. Heat the part until water sizzles, and do it again. Keep at it until it looks like you want. If you give it enough coats it'll look black instead of brown - my last TC hawken came out that way after around 25 coats. It's not brown, but looks quite nice. Make sure you have good ventilation, the nitric acid fumes are rough on your lungs and eyes. Watch out for splatter, anything that stuff hits is going to rust. Otherwise, it's pretty easy to use stuff. Never tried the other brands, folks say the Laurel Mtn Forge kind is really good but I don't have any experience with it.