Hi Dave,
I went through the same process and turned a beautiful mouthpiece--only problem was that it did not resinate at all. All hat and no cowboy. I then made another one with a 1/4" hole and tapered the inside so it created a cone--resonating chamber--using a drill and a taper bit. I have seen many old examples of this type of horn and all are pretty loud and create a solid tone. That being said, I am stillworking on finishing that horn, but it sure can call the dogs--just ask my wife. I blew it in the basement to check the tone and the dogs on the 3rd floor went nuts! Hope this helps...