I'm with old bear, I believe that to be excessive leading. I would tone your charges down or switch powders or bullets. Cleaning up that mess can be done, but go easy and don't worry about getting it all the first time. I leaded up my Model 14 pretty bad and got the lead off the outside of the cylinder and top strap by saoking the gun in
Ed's Red overnight and using a scraper made from a heavy gauge copper wire. I tweaked my loads to stop leading and the lead on the cylinder face eventually wore off after a lot of shooting a few regular cleanings.