J-B is a wonderful barrel cleaner, I have restored several rifles to tack drivers with it. Had one pre 64 mod 70 that had a barrel that looked like a sewer pipe when delivered to me by my dentist to clean.
He was of the school of put oil down it and put it in the closet. I started with Hoppies and a bore brush, after an hour or so I change to J-B then hours of more cleaning before it came out clean.
Groups went from 3 inch area to under one inch. Not bad for a 30-06.
That said remember J-B is an abrasive a very fine one but still an abrasive over use can wear a barrel. Just get the bore nice and shiney
and it will pick up less copper. Hold the J-B off for times when many rounds have been fired.