I start with a clean barrel, and then wipe on a coat of cold blue, all the different brands I’ve used worked about the same. Next, emmerce the plugged barrel in a 50/50 mixture of chlorine bleach, and distilled water. Don’t breath the fumes coming off this concoction, it will turn your light out. When you get the pitting you want, wash the barrel in clear water, and wipe it dry. Next I apply Birchwood Casey’s plum brown around the places patina would naturally accumulate, and hit it with a heat gun to get a good light red brown. When I am satisfied with the colors, I rub them back with an extra fine Scotchbrite pad. Oil, or wax the barrel to stop any further oxidation. Sometimes you have to give the barrel a baking soda and water bath to stop all the chemicals.
Hungry Horse