Although I am the first to say, 'go slow when building' I think that applying a cold blueing is not the time for it.
Properly done, you should have the entire barrel coated in less than a minute.
When blueing your barrel, you should degrease it and wear some rubber gloves (like your wife has under the kitchen sink) so the oils on your skin do not contaminate the surface.
You can degrease it with Brake Cleaner, pure alcohol or acetone. (do this outside).
Pour a little of the blueing (maybe 1/2 ounce) into a cup you don't want to keep and dip a small piece (about the size of a .25 cent piece) of #000 steel wool into the solution. (It's best to degrease/dewax this before using it).
Rapidly rub it onto the barrel from end to end covering as much area as you can. Re-dip the pad if it seems to be drying.
Now your barrel will have streaks and look really bad.
Let it set for a little bit, wash it off with water and dry it with a paper towel.
Throw out the old solution and pour 1/2 ounce of new solution into the cup.
Repeat the rubbing with a new pad dipped into the solution only this time rub much harder making a little extra effort to cover the bare/light areas.
Again let it sit, wash and dry it. It should look better.
Repeat this coating/rubbing at least once, and 2 or 3 times is even better.
After the final washing and drying, apply a good rustproofing gun oil and let it sit over night.
In the morning, it should look so good you will start eyeing other guns around the house.
Just a thought about cold blueing though. It is not as durable as rust blueing or browning.
zonie