I used Allen's process to age a Southern rifle a couple years ago with good results. I draw filed the barrel, sanded it with 220 grit paper, and used pentane to clean the barrel before applying the browning solution. I applied Homer Dangler's cold browning solution three times a day for several days without carding during the process. I checked the pitting process on the bottom flat of the barrel, and used coarse sand paper to remove the scale from the surface of the barrel once I had the amount of pitting I was wanting. It is a bunch of work to remove the scale. After removing the scale, I applied 44-40 cold blue solution to the surface and used steel wool to pull it back to the gray black color I was looking for as the final finish. It requires work, but makes a good looking aged finish that I like. You can see the rifle I used it on by going to Art Riser's contemporary makers blog and search for "Roger Sells". The rifle is stained dark and has two grease holes in the butt stock. I hope this will be of help.
Roger Sells