As seen in the sketch I drilled the inside of the antler down to the end of the tang. I used a broach to get a good fit and tang/ antler fit.
I then soldered a #8 machine screw to the tang. I drill a hole and then slot the end of the tang. I sand the head to fit the drilled hole and do a bit of peening to get a good fit before completing the solder.
I then drill a hole at a right angle to the stag butt. I drill the hole a little larger than the #8 screw to have some allowance in the hole.
I then counter sink (at the butt end) around the drilled hole with a Fostner bit deep enough to accept the thickness of the #8 nut.
The next step is to fit the handle onto the tang with the screw threads extending through the counter sink hole and check for fit. I remove the stag and put a piece of blue tape over the butt end and pierce the tape for an air vent. I fill the tang with epoxy about 3/4 full and fit it over the tang.
I set the knife in the vise blade down and using a small socket screw the nut onto the screw and tighten the handle to the bolster. This locks up the handle and tang. I clean up the area that epoxy has leaked as well as the bolt threads.
After the epoxy has cured you can finish the butt anyway you want. The key is having a square butt and 90 degree angle on the bolt if you want to thread a end cap on. Or you can just use as much of the protruding bolt as you want to help affix another type of butt finish.
This is the way I do mine. Others probably do it differently and more efficiently.
At this point