The 45-70 killed a lot of buffalo. Buffalo Bill used a 73 Springfield. Sharps gets the credit for being a buffalo gun, but that came along after the 73 Springfield. Besides buffalo, they were used to hunt elk, deer and antelope. Indecently, the government loaded some bird shot loads for the use of foragers to hunt with. Yours is not a shot load, like Nova said, the R stands for rifle, a C instead of an R meant it was a carbine round, and was loaded a bit lighter than the rifle cartridge, but they both looked alike is the reason the the head stamp. Your cartridge is an inside primed version, the crimp was to hold the primer cup in place inside the case. You are very fortunate to find an empty in that good condition. The Indians had figured out a way to reload those inside primed cases, so the soldiers were under orders to mash the empty's so they couldn't be reused. Did you find the case in Florida?