Update on the carding wheel. I got one from Brownell and used it on my barrel. I put a 1/4: bolt through it and held it in place with an aircraft nut. I ran it at the slowest speed and it didn't do much but I am now running it around 5-600rpm and its working pretty well. I don't want to take too much off this barrel just want to remove the rust and some of the worst pitting.
Up above in posts you will see my carding wire wheel in a box. The lid has a hole in it for the arbor shaft to stick thru. I keep it in that box so it doesn't get contaminated with shop oils, sprays, oily hands, etc. So make sure that barrel you are using it on has absolutely no oil on it or you will contaminate whatever you try to brown every time you card it. Also, a carding wheel will not remove any metal.
As for the rust brown or blue. The brown has proven to be very durable & easy to maintain.
The rust blue has proven to be very easily worn off & not durable at all. (For me) I blued 2 dif barrels as black as coal. bout 7 yrs later both of those barrels are now light blue & they have never been used, other than cleaning. So evidently my rust inhibitor oil is doing a heck of a job, and removing the bluing as well.
The only bluing I have ever seen hold up well was hot dipped bluing, such as seen on modern firearms.