For what it's worth, the folks at Bartlein barrels very strongly recommend against using JB Bore Cleaner on a NYLON bore brush. They have repeatedly verified that the nylon brushes, for whatever reason, do not follow the rifling grooves down the bore. They skid across the tops of the lands and cause serious damage when combined with JB. I've seen some of their borescope pictures, and the bore looked like 20 miles of bad road! I still use JB, but not on nylon brushes!