I also have never had luck with a template of any sort. Others have. The diameter of a horn changes constantly so you are never working with a flat surface. A friend of mine is a tattoo artist and he gave me some interesting pointers. He free hands all of his designs on the person for the same reason. For example, a circle on a horn, is not really a circle, it has to be destorted to appear that way on a horn.
Cory Joe