I should add that IMHO using a piece of bone, antler, horn alone as a friction fit finial is probably not the best idea. You will see old horns with a separate friction fit plug, late Phillys as well as some Va. horns come to mind but they usually have a wooden plug. The wood, both woods, butt and finial will swell and shrink but can be pushed in to fit tighter. My thinking is the others horn, what ever is to hard and will after time polish the inside of the hole to the point where it will not be easy to keep in place.
Part of this thinking is in making horns for sale, I want the customer to be happy and not have a horn that I think to start with will give him problems. Same reason I pin all my bands rather that just heating and pressing them on.
M2CW, Tim