Hi Jeremy-There is no indication of a fastener of any kind on the butt of the MA horn, and the front 'carry ring' is almost too small to hold anything. My suspicion is that it was simply kept on a shelf or, on top of a cabinet to be held in reserve for refilling the hunting horns.
Here are some numbers on it: Outside curve is 26 inches, inside curve is 25 inches. Butt is 3 and three fourths inches at its widest. I am struck by the small diameter of the spout hole. It isn't much more than three sixteenths of an inch. Not sure why this is so tiny, but it may be that it helped keep moisture out, the horn was never really finished off, or...?
Glad that you like it and that it could give you a pattern to build on your horn, which has great color by the way. Just for fun, maybe add some scrimshaw? Would look great.
Dick