Welcome:
Lots of help here. Please keep posting. Tx.
Suggest reading the "SORI" Section as you get going.
Ken Howell's book: DESIGNING AND FORMING CUSTOM CARTRIDGES, has rim diameter dim's for 44-40 and 45 Colt.
"BLAIR", here, is versed in the Schofield round.
RIM OD's range between .500" for 44 S&W American to .512" for 45 Colt (not "long" COLT) to .515" for 44 S&W Russian, so those are all close to the same.
56-56 and 56-50 rim OD's range between .630" for STARLINE brass to .650" for most others.
There are no recent SAAMI dim's for 56-56 or 56-50, which SAAMI notes are "obsolete cartridges".
Please let us know how you do with your Spencer.
Please Google: Spencer rifles in movies, for some nice scenes.
SAFETY FIRST!
PLEASE USE BULLETS WITH A FLAT SPOT ON THEIR NOSES GREATER THAN THAT OF THE CENTER FIRE PRIMER AND LOAD WITHOUT LETTING THE ROUNDS SLIDE TOO FAST INTO THE TUBES OR BUTT.
All the best,
El Supremo/Kevin Tinny