It's been my experience that BBS will remove LIGHT copper fouling if left to soak overnight. I've proven it to myself over the years with countless before and after borescope inspections. Soak it, stand it in a corner, muzzle down & in a small, white, plastic pill bottle, and the next morning the solvent in the bottle will be some shade of green.
Actually, I don't want to remove all the copper anyway, since taking it down to 100% clean, bare metal will require anywhere from 5 to 10 fouling shots before the barrel(s) settle down & shoot their normal tiny groups. As for carbon, I also leave a little carbon remain. All I want to do is to keep it under control.
Bartleins, Kriegers & Harts all shoot better with a little fouling present, and it works for me with the first shot fired in a match going into the point of aim. Really frustrating when that first shot goes somewhere else, and there are no sighter shots allowed.
For the really heavy coppering barrels ( only a few, old collector military), Warthog-1134 and Sweet's are the choices. The label on the BBS bottle says nothing about a time limit for leaving the solvent in the bore, as does Warthog & Sweet's, so right there is a big clue that copper removal is not it's high point.
Not claiming to have the bottom line answer ( I don't think there is one), just what works for me.