I use a Nylon Brush, if I use a Brass Brush it's just one time down the Barrel and out. I dont use BH but I thought that stuff was suppos-to be pretty darn, your Barrel has been this Dirty for 1 1/2 Years? or getting this Bad for this long and Your Accuracy has'nt Suffered? Good thing BH 209 is Non Corrosive and the Least Fouling of any of the other Powders out there and requires No Swabbing between shots.
Now I dont know what your suppos-to use to Clean BH209 so I wont comment on what to use. One thing I will recommend is getting some Montana Extreme Bore Conditioner and treak your Barrel with it. After each cleaning session run a wet patch of MX BC down your Barrel and leave it set for awhile, then 2 dry patches and load. This stuff works great to help Protect Your Bore and makes Clean up Fast and Easy.
What kind of a Barrel do you have on Your TC Omega, Blued or SS. Regular Blued Barrels react different to Chemicals and such than a SS Barrel does, what has your Patches been looking like after you usually clean and whats's your Cleaning Method now.
I hope everything works out for you and you get this figured out.
(BP)