When I bought my Argentine rolling block "contemporary sporter" (meaning it had been bubba'd in antiquity), I got an open box of UMC commercial loads, 385 grain lead alloy bullet, one of which I fired; I then removed the huge berdan primer and drilled and chamfered the pocket for a shotgun battery cup, and that was THE case for a few years. That was about 35 years ago. That one case was fired several hundred times and is still useable, but I have found other options for brass (see other post on .43 Spanish).
I also bought a bunch of military ammo, all dated 1884 to 1888; folded head case, and brass "jacketed" bullet. This also fit the rifle, and some would even fire, but the cases being old and brittle would sometimes split and stick. I disaasembled most of the military stuff, popped the primers (those that would, any way); pried out the primers and gave them the shotgun battery cup treatment. With the Lyman 439386 bullet and 50 grains of FFg, they held up well. I still have some of those "jacketed bullets", and I often wondered about them. The case dimensions were identical to the commercial UMC ammo, or as close to "identical" as you can get within manfacturing tolerances; they were not "different" from the UMC cases, and both were bottle-necked.
Resp'y,
Bob S.