Milton,
The Rem's are about .945 on the ring. After that's milled and slipped off, 'tis down to .917 + -, which chambers in the 1883 gun. I won't cross my own line in the sand by using smokeless in one of these old dogs (a compatriot, familiar with BP, loaded smokeless one night and double charged a round and blew up a perfectly good buffalo gun.
Lived (real lucky) to tell about it!!!).
3 oz. zinc?!? Sounds like your speaking of the klinker guns. Found them on line, still made. A single barrel pedestal gun, with shield, fired with a lanyard. I'll stick to shoulder guns.
Thanks for the come back.
Best,
DD