Normal bore cleaning won't remove hard carbon fouling. You have to remove it mechanically, and JB does just that. The thing is, unless you have a bore scope you usually can't see if this fouling is present, or if you have removed it. But JB does indeed work for this, and sometimes significantly improves accuracy after it has been applied. Just as Gun nut says, there is no need to use it all the time, but when you need it it's valuable. BTW, I just got a new can of it, to replace the one I have had for around 10 years. It's Gray now instead of brown, but smells the same and seems to work just fine. I apply it by smearing it on a large patch, which is wrapped around a bronze brush much smaller than the caliber of the barrel. I mark the rod for the ends of its travel, and start scrubbing. Usually I'll do 50 passes each way, then look with the bore scope. I keep this up until the carbon is gone. Sometimes 50 strokes, sometimes thousands. Just depends on what's in there.
