The blacked out crown is often buffalo horn fitted in and polished.
There is a good tip, when fitting spacers between antler and shaft, but it looks like you may have used it. If your using threaded bar,- roughen up and damage the thread on the bit of bar thats going into the handpiece, or it could just unscrew when the araldite has set. Then glue the spacer in place, and put a washer and nut on, and screw up the nut tight and leave to set. When set remove the nut and washer. This works great also if your using a horn spacer,- warm the horn spacer first, and the nut and washer will force the