I've never had very good luck with Birchwood Casey cold bluing except for touch-ups. Ditto for BlueWonder. My current go-to is Brownells Oxpho-Blue. It's pretty hard to predict how deep and uniform the bluing will turn out on any of these cold-bluing products before you start, but thorough (and I mean obsessive) degreasing is an absolute must. After the usual surface prep (and yours sounded very thorough) I use the strongest commercial degreaser I can find (spray-on brake cleaner, followed by a wipedown with denatured alcohol with clean cotton cloth usually works for me). Use clean nitrile or cotton gloves when handling metal, as skin oil fingerprints can really mess you up. Lightly heating the cleaned metal in the kitchen oven (preferably while spouse is distracted or out) or a heat-gun seems to help with most cold bluing products. Remember that surface rust will start forming very quickly after degreasing, get right on to the bluing after degreasing. If worst comes to worst, you can always remove whatever botched bluing you wind up with (and try another cold bluing product. Duracoat makes a good bluing and rust remover.
I've tried spray-on epoxy based finishes (Duracoat) with some success on guns with poor finishes, but in my opinion the results never look as good as bluing. It's a pretty durable finish, but it will eventually chip and show wear.