Hey deepvalley. I have an old Forehand Arms 12 ga. single barrel that was mfg circa 1896-1908. I don't know about your gun, but mine has a cocking hammer and doesn't require caps, so it was built to use shotshells:
Here's how I converted it back to shooter from wallhanger:
I DID NOTHING TO THE GUN beyond having it checked out for safety; then I just cleaned and oiled it. But I did buy ten 2 5/8 inch, 12 gauge lathed brass shotshells from Rocky Mountain Cartridge Co. These are considerably thicker-walled than extruded brass shells. I may be wrong, but I feel like they provide an additional margin of safety for my guns old chamber. They were pretty pricy, $65 for the 10, but can be handloaded and reloaded innumerable times without buying a lot of expensive automated equipment. They should outlast me.
So far, I've only used them with blackpowder loads (actually Triple 7, a blackpowder substitute), but I'm planning to cook up some "vintage" (i.e., low powered) smokeless loads too, using Red Dot powder.
It's been a lot of fun learning how to load these things, finding the right components, priming them, depriming them, loading them, shooting them, talking about them, and corresponding on the forum about them with others who do this or may be interested in doing so. And everybody locally around here who sees them thinks they're cool. They're great conversation pieces.
But best of all, these lathed brass hulls have made my old gun which hadn't been shot in about 40 years, a useful shotgun again. I call it my "fowling piece" (although I haven't actually taken it "fowling" yet). But I patterned it at 25 yards using an ounce of #7 1/2 chilled lead shot, powered by a light load of Triple 7. My handloaded shot peppered a thin cardboard 3x3 target with about 150-200 holes. I had an empty Coke can sitting behind the center of the target. Ten of the #7 1/2 pellets hit it and penetrated through both sides of the can. Another pellet hit the cans reinforced rim at an angle and dented it badly but didn't completely penetrate it.
All in all I think its going to be a great bird gun.
Maybe a few of these brass shells would get your old gun off the wall and make it useful again.