Well, I did the Krieder break-in normally used on new rifles, on my S&W Mod 27 with an 8 3/8" barrel and saw a remarkable drop off in fouling and a reduction in shot spread (grouping) from about 7 inches on the first 5 shots to around 2 inches on the last 5 at 25 yards. I registered every shot from the first to the 25th. Of course the first 10 were days apart so sight picture variations could account for some of that spread, but the fouling dropped off significantly owing to a smoother bore. The gun is very accurate now--much better than I am with 6+ decade eyes, and I can't help but believe that much of that is due to the break-in routine. Also any leading and/or copper fouling is wiped out with a tight patch.