Early self contained cartridge stuff was mostly rimfire. Low pressure, so the stronger case head wasn't needed. These were popular with some union units, especially cavalry, when they could get them. More ruggedly constructed than the first henrys. Downside was that the spencer was a bit more annoying to load (loading tube through stock) and had a slightly lower capacity.
ETA: your friend appears to have a cavalry carbine at first glance. Most likely a 56-56 spencer round.
I would have thought a dead hooker. But his find was good
Dead hooker bones?What are you thinking, man?
A dead hooker won't keep long in an attic.