I have a uncle that showed me his original Spencer rifle today. It is carbine length. I told him that I would try to get him some info on this gun. He said that he thought it is 52 caliber but I think it is a 56-50. I have one of the fired cases and here are some of the measurements.
case length- 1.128
inside case diameter-- .514
outside caes diameter--.557
This case is not a rimfire. It has a primer but it looks different look than a regular rifle primer.
If any of you has any info on this gun or cartridge that you can share I would appreciate it