Never did get a decent looking cold blue on any barrel I tried with a Birchwood Casey product and a barrel is easier to cold blue than a receiver.
As pyscodog suggested, the Blue Wonder cold blue kit has worked pretty good for me. 2nd to Blue Wonder on satisfaction of finish for me, has been Brownell's Oxpho Blue. The Oxpho is easier to use than blue wonder and costs less. I've seen a barreled action done by a gunsmith using Oxpho that was reallllllly nice looking. Owner of a gun store that showed me the Oxpho blued barreled action for a truck gun he had built was very impressed with it too. But suspect, the gunsmith dipped it in a tank/trough of Oxpho to get the results.
Anyway, with the Blue Wonder, you can apply numerous coats with it and it should increase in darkness/coverage leading to a decent overall finish that does wear well. Mind you, Blue Wonder will oxidize/rust during its curing period. You darn well better keep it well oiled during this time. Also, metal prep for application of Blue Wonder is more critical than with Oxpho. Don't need to concern yourself about oxidation/rust with the Oxpho either. Oxpho wears fairly well too, but you need to make sure your first coat of it is done right. Meaning use numerous pieces of soft absorbent cloth, each wet, not damp, to apply it. More Oxpho you apply in first application, frequently using a fresh piece of cloth, the better should be the results. This is true for Blue Wonder too.
By the way, I've watched one of the creators "aka Chemical Willi," of Blue Wonder Cold Blue demonstrate it at a couple of local gunshows here in the Houston, Tx. area, where it orginated as one of the RB line of gun products. Earlier post, mentioned seeing it demonstrated using a shotgun receiver with great results. Reason the shotgun receiver was used, like I watched "chemical Willi used, was basically because the softer metal in a shotgun receiver takes a cold blue much better than a hardened rifle receiver.
Having written this, chuckle, nothing better than a good hot blue job or rust bluing.