Yeah, .45 or above. They used to hunt them with .50 cal. Sharps. I haven't shot my 1886 Winchester in decades, but when I did, I had to neck down .45-70 casings to fit the 40 cal. It shortened the casing a little, but worked.
Yea, forgot about the .50-70 Sharps.
It wasn’t until we moved to Wyoming that we learned firsthand just how early the herds were destroyed - the slaughter really was getting going as early as 1870. The southern herd was largely destroyed by 1872 or so.