I have owned a few of these, all have had filthy barrels. I normally run a phospor bronze brush down the barrel with hoppes no 9. If that dont get them clean nothing will.
One rifle i have an old 1910 imp mod d is well & truly shot out lord knows how many rounds its fired. If you load a pellet & push it through the barel with a cleaning rod it skips the rifling about halfway down. It tends to throw flyers!
Another standard on the workbench is cosmetically challenged but has a perfect barrel. Winter project me thinks!