the new made replicas shooting the center fire version wich is made by starline

RCC offer the center fire version

and also the rimfire cases ( for 6 mm flobert blanks as primer) for two different bullet diameter

https://www.rccbrass.com/56-56-spencer-rimfire/

RMC having the 56 -56 and the 56-50 center fire case for original but conversions and replicas

remember the 56-56, 56-52 and 56-50 are all interchangable and the old bigger diamter were all abandoned for the 56-50. don't ask me how they were shooting in older rimfire guns with bigger barrel diameter. this was about outside lubrication changed into inside lubrication, maybe the 56-50 had a hollow bases.

fact is the 56-50 romano must be something else. my first thought was "lathe turned 32 ga brass case"

https://www.gunsandammo.com/editorial/7-shot-wonder-the-spencer-repeating-rifle/248815

this is what the RMC headstamp looks like but this could be changed over time

https://www.youtube.com/watch?v=-a1oFeLPAxw

a .533 Minie fits very well into the cylindrical 32 ga magtech brass case so the lathe turned case with a thicker wall may hold a .520 diameter bullet.
the rim is looking different on .52 Romano so it don't fit into 32 ga shotguns. I have made 12,7x60R 500BPE ( a short german version of the 500 BPE) by using 32 ga magtech brass, you can use it for different stuff.