I had the pleasure of shooting several California quail (and missing several...) and a cottontail with an 1865 Maynard's .55 shotgun barrel some years ago. The guy who owned it had original reloadable Maynard shells (about a dozen) and had loaded them with 1/2 oz of 7 1/2s and black powder, using (I think) 28 ga. wads. It seemed like shooting a (smoky) .410 to me and was about as quick (or slow depending on your POV) to load as a standard modern hammer "1/2 double" as one of our members calls 'em. He also had the rifle barrel, a .40-40 with a near perfect bore.
The buttstock of that gun was OK for the ".410-like loads," but I wouldn't have wanted to shoot it with a .64 or 18 ga. barrel and more powder and shot very much. Skinny and sharp edged; make your fillings wiggle. No forend to hang onto, either. But a great accessory for the rifle, if you had only the one gun.
