BreakFree CLP on the magazine tube and rings of your gas gun. You won't believe your eyes.
Spray it on your dirty gun.
Shoot a box of shells through it.
Wipe off the previously caked-on carbon with a rag.
Reapply.
It's amazing stuff.
I agree. Spray the hell out of it with Breakfree CLP and shoot it "wet."
Good luck!