I find that different barrels "like" different bore conditions.
Some time back, a friend, who is an avid long range varmint hunter, got a bore scope. (Those of you who have one know what I am about to write.) At first it seemed that anything that he saw in a barrel, no matter how small had to be removed. After becoming more experienced he finally arrived at the conclusion that cleaning to bare steel was not needed, given that he wanted his barrels to last for as long as possible, and that perfectly clean required the use of abrasives, more frequently than he liked. After he became more experienced, he began to develop some judgment about what is important, and what is not. I call his earlier condition "bore scope disease". The truth is that you do not have to get a barrel perfectly clean for it to shoot well, just clean enough, so that it at the same starting place each time. I clean my 6PPC barrels less than I used to, and I get fewer surprises. I do pay particular attention to the end of the neck part of the chamber and throat when I clean, since accumulations in that area can cause problems. So far, with 133, Butch's, patches, and bronze brushes, my barrels look good when they are scoped. As far as the relationship between hard carbon and copper goes, it has been the conventional wisdom that in a smooth barrel, carbon accumulation will strip copper from bullets, and that if ineffective cleaning methods are used, alternating layers of carbon and copper will result. This used to be seen, a lot more often, when less effective bore solvents were the rule, and 133 was not in the powder mix. Back then, no one that I knew had a bore scope, and a home made copper solvent called blue goop, that was made with (cringe) 28% ammonia, was used by some shooters to deal with copper that had accumulated due to the ineffectiveness of off the shelf bore cleaners. Then Marksmans Choice, later renamed Shooters Choice, and Sweets became available, and at that point the use of strong home brew cleaners started to diminish. BBS came along later, and is what I currently use.