Been out of town, just saw this one. If you have access to a bore scope that would be the best way to determine what is in the bore. If you haven't succeeded yet, try JB Bore Brite Paste or JB Bore Paste. Using a bore brush, dampen a cotton patch, wrap it around the brush and apply some JB. Works pretty good. For copper fouling, run two or three patches wetted with BoreTech Eliminator and let soak for several hours. Then run bore brushes with Eliminator thru the barrel. Use dry patches to dry up the bore. Might have to do that several times.
If you let Eliminator soak for several hours, it will lift copper residue of a barrel. If you use a brass jag or patch holder, you will see blue right away. Eliminator is hell on copper but will not harm barrels. That is what I use now to clean my rifles and pistols. I have an use a bore scope so I can see what is really happening. Shining a light down a barrel does not really tell you anything.