IMO, there are a couple of factors that contribute to carbon build-up. The first is that many factory grade barrels have a fairly rough finish and even attempting to smooth them out with an abrasive(JB, etc) may not fully resolve the issue with completely smoothing the barrel and reducing carbon accumulation. Custom barrels(Rice, GM, etc) with the possibility/practice of finer finishing seem to be less susceptible to build-up. The other is cleaning method. Carbon is not water soluble, and even with the addition of soap/detergents, the patch may come out clean, but carbon build up may bond to the barrel, particularly in the area where the carbon ring/resistance is felt. I have had very good success, not only with my own rifles, but a few of my buddies experiencing this problem with their rifles, cleaning/removing carbon build-up using MAP(Murphy’s, Isopropyl Alcohol, 3% Peroxide/ 4:6:6 mix). While not historically correct, and many opinions about the using 3% peroxide in our barrels, it does appear to be quite effective in removing carbon build up in the barrel/breach. The peroxide content(weak acid) ends up being less then 1% of the total solution, and only exposed to the barrel for about 5minutes. After years of use, and careful inspection of my barrels, I have seen no ill effects on the barrel, as well as no carbon accumulation when using a bore scope. Interestingly, when the solution is poured out of the fouled barrel after 5 minutes and subsequently swabbed dry, there are no signs of black/carbon in the effluent, used patches, or the barrel/breach. It is claimed that the peroxide(MAP) complexes with the carbon resulting in the peroxide and carbon, forming water, carbon dioxide, and hydrogen. The small amount of peroxide deactivates(oxidizes) when exposed to the carbon. The Murphy’s, alcohol, and residual water assist in solubilizing(cleaning) the salts and other residues. Much like many shooters, when in the field, I will clean with water or a mix of detergent and water….But will follow up at some point later, using MAP “chemically” to get rid of residual carbon. Just my approach…