Here's a small rough surfaced horn for your viewing pleasure.
5 inches along the outside curve and the spout hole diameter is 3/8th inch. The base plug is approximately 1 and 7/8th inches by 1 and 9/16ths inches and is secured with 8 small tacks. Empty and without a stopper when found.
It was in a wooden box with some other gun stuff (12 gauge wad punch, some homemade card wads, etc) at a circa 1980 farm sale.
Enjoy,
Kevin