I saw this horn, or its twin sister years ago at a rendezvous. It didn’t have the blade attached then, but may have had the screw hole.
At the time there was lots of discussion about if it was antique, or aged modern, the general consensus was that it was modern. The reasoning had a lot to do with its numerous opportunities to leak powder, and it relatively complicated mechanism. I know I’d be afraid to pack it around in my pocket, and then shoot a flintlock.
Hungry Horse