Brownell's sells a hone made for guns. Or you can get the inside honed for about $200 at Skeet's gunshop. If it's not on the inside, you're steps ahead. Polishing and reblueing on the outside isn't going to remove a whole lot of metal, but it may leave some pits...blued pits, which isn't so bad.

I've used Oxypho blue, also from Brownell's, for good (the best cold blue I've used) results. Got to degrease the barrels first, of course. Fingernail polish remover works great.