Scrub that barrel out with lots of penetrating oil and steel wool, then further smooth it by firing a dozen or so light loads with patched round balls, with the patches coated in fine valve grinding abrasive paste. When you can run a patch down the bore without it catching, it should be smooth enough. Its accuracy may surprise you. I'd bet its 1-48 twist, so try both round ball and conical loads for accuracy. I'd probably bead blast the exterior metal, and apply one of those spray on, bake in your oven finishes, along with a stock re-finish with oil for a nice, inexpensive hunting rig.
Larry