I've been using JB for over 24 years.....
I also make my own abrasives.
On large over bore cartridges or after a large number of shots such as p. dog shooting, use the followiing method: Push 3 patches of Montana extreme through the bore to get rid of the loose powder fouling. Then take JB and work it into 5 patches. On a tight Punch type jag, scrub the bore with short strokes back and forth. Follow with 5 patches soaked in Montana Extreme's 50 BMG copper solvent, scrubbing with these patches also. Your copper will be gone with this cleaning method.
We developed this method in the late 70's and early 80's when p. dog shooting was 650-1200 rounds of centerfire a day. We did use the good Hoppes at that time along with a mixture of "blue goop" for copper removal.
Most brushes are good only for 100 strokes max, then they are trash. I save them and in extreme cases will brush with JB using these wore out brushes.