Is there something that would do a similar finish by wiping on the metal, rather than immersing it? I don't have the space or equipment to set up a boiling trough for a long barrel here.
Yes, wipe the barrel down with cold blue, hang it by the tang (muzzle pointing down) and then use a spay bottle with bleach in it to spritz bleach on the barrel. You will get a random pattern. If you don't like what you see, do it again. I do this hanging it down off a fence. In the summer, humidity really does a great job. If there are colder non humid days, hang it in the shower and when everyone takes a shower the heat and moisture will do the same thing.
You can also use straight bleach, apply it cold and use a torch to boil it off the metal barrel, it will give a different affect.
I used blueing and bleach on this gun. Didn't like what I saw, steel wooled it off and then used bleach and a torch on the barrel. The lock has a combo of blue and bleach. The guard, trigger and screws where soaked in a 50-50 mix of bleach and water for a day or so, then cleaned and oiled. The barrel showed a good pitting that for the most part looked like an old rusty barrel, which is what I wanted. I used old original barrels as a barometer to judge the outcome.