I think it is a cowhorn, not a buffalo, though admittedly I've never handled a buffalo horn. I'm also not sure we should assume that the use of paint indicates Indian use.
The horn walls at the butt end are pretty thick and are uneven - that is the way they tend to come from the cow but most old horns I've seen have been thinned and evened out, even the pretty rough ones. That seems kind of unusual to me, and makes me wonder if this isn't a costume or early muzzleloading revival period piece from the 20th century. OTOH, that tip treatment would take some work to make, and it could be a period piece that was shortened at some point - that would explain the nice shaping at the tip and the body with the amateurish work at the butt end.