Holy crap! Do NOT sand your barrel! Soak it in vinegar then rub it down with green scotch brite pad. The vinegar reacts with the bluing and the scotch brite rubs off remaining bluing. Soak it for a couple mins. As soon as you drop it in you'll see it start to bubble. It will have a bit of a rusted looked to it but after you rub it, it'll start to look cleaner. After you've removed the bluing then polish it with a polish compound (i use mothers mag and aluminum) and a rag! No SANDING! Sanding internal components changes dimensions and even the slightest change can affect the firearm.
Also, remember that the bluing is a protective coat. It protects against rust so you risk rust forming unless you keep on top of it or do something like clear coat duracoat.
If you've got one foot in yesterday, and the other in tomorrow, than you're pissing on today.