You might try steeping the piece of antler in warm/hot water for an hour or so before turning. This will somewhat soften the surface and facilitate easier turning. Be sure to use antler that is as solid as possible, either from tip or crown base depending on your purpose. Avoid using the pithy part as much as you can. It will often crush and not hold form in use later. For a powder horn tip, it is best to get a piece that will turn true and still be about 1" in outside diameter, to assure a good result. If you can get the crown of the antler still attached to the skull, cut it from that section and utilize the bone from the skull also.