Remembering back 10 years or so, we used a Wilson neck sizing tool to resize cases. Every so often, every 10-15 reloadings, we would run the cases through a F/L die if they got really tight. Now, with the loads we are shooting today, we F/L after every loading. That is part of the barrel life problem.
Jim Borden wrote an article a few years ago just about when BBS and MX was starting to be used. He made a pretty good argument that excessive Ammonia, in a hot barrel, was contributing to early barrel failure. Sweets has been used for years but they changed the formula some time back. The old bottle instructions was to wear rubber gloves when using Sweets. That message is gone now.
Recently I switched back to Hoppes #9 since I have had no coppering problems in years.
As to carbon rings, there are two carbon rings that we must contend with. One ring, and it must be brushed out using a larger brush and a twisting motion, is the ring at the end of the chamber neck. The other "ring" is in the bore itself. If you are having a buildup with the powder/load you are using, you can feel this ring with a tight, wet, patch. It can be chemically removed (Sweets, Wipeout, GM Top, etc), abrasively removed (Iosso, JB, etc) or brushed out or a combination of these.