Leighton, I've gotten the same kind of improvement in barrels with an even patina by spraying them down with WD-40 and letting them sit awhile before rubbing with 0000 steel wool. WD-40 seems to loosen loosely bound rust, but does not remove the more tightly bound rust of the original blue or brown. That is why I never use WD-40 on freshly rust blued or browned barrels.
In case anyone does not already know, different colors of Scotchbrite pads have different abrasive grits impregnated. The chart Ken61 provided a link to is very helpful, but I'm surprised it does not have the grit equivalent for the commonly seen green Scochbrite. I know green is coarser than the maroon used here by Stallones. A very fine Scotchbrite would be advised for this type of clean-up.
