The barrels actually look pretty good, I'm not sure if anything is really necessary. The twist pattern is very visible, and the color looks fairly black. To keep it original, lightly remove any rust with bore cleaner and 0000 steel wool. (Or Frontier Pad). Degrease with acetone, then relacquer.
You can either use a spray can of clear gloss lacquer, or buy a bottle of clear gloss nail polish, cut 50/50 with acetone, and brush it on with a small, square tipped artist's brush. Same with action.
Use Renaissance Wax on all surfaces, including the wood.
