The action of the solution used to rust blue the barrels, causes them to "rust" in a controlled manner.This causes microscopic "pits", which both gives the satin finish and wearability.The final polish is usually with worn 320 grit cloth.A high polish doesn't want to rust,especially if hard metal(like a bolt shroud),sometimes requiring repolishing with new 320.I never tried to get a shiney finish, so I can't say with authority, but a coat of paste wax after normal blue, may do it.
Mike