Have you tried outers foaming bore cleaner yet? I was surprised how well it worked and how much scrubbing it eliminated.

On tough bores, I alternate between three poructs:

1) Outer foaming bore cleaner, let sit in bore for 1 hour, wipe out.
2) hoppes Elite Bore Gel. Let sit overnight then wipe out.
3) Hoppes No.9 Copper formulation. Let sit 2-3 hours and then wipe out.

Repeat as necessary.