I love it! We wonder about the bison from which it came, if it was killed in Tennessee. I see that horn is more brown than black, also, which I understand is a characteristic of the eastern variant of the plains bison (wood bison are only in the far north). I think your horn is not only a nice artifact to have, but may be historically significant from a biological standpoint. You would probably enjoy reading Ted Belue's The Long Hunt, which tells the story of the extermination of the eastern bison.
I would also like to suggest that it may not be a priming horn. It might very well be a "day horn" or "bag horn," carried in a pocket or pouch by a hunter who only expects to shoot a few rounds, maybe collecting a few squirrels for the pot. There's no need to carry a pound of powder for an outing like that.
In any event, whoever carried the horn was free to use it for whatever purpose he chose. You are lucky to have it!
Thanks for showing it to us!
Notchy Bob