Info on Italian BP rifle

Any help appreciated. My brother picked it up someplace. It seems to be a .45 cal, side lock percussion, but looks more like a TC inline. Double triggers, hammer won't cock until the "set" trigger is pulled.Has a nice walnut full length stock. The only markings are.."Fudamanuarms..Made in Italy..Kal 45." Octagon barrel is around 27 inches long. I have a pic, but haven't figured out how to post them. It will load the plastic band from a .45 power belt, but the slug won't go in. Cleaning patches keep bringing out rust, so it's probably just too fouled to load. Any ideas on how to remove that much rust? It's really a beautiful rifle, and looks almost new on the outside. Is it possible it needs a smaller diameter .45 ball?

There are no bad guns, only bad people.