I have never handled on in person but from pictures it looks like the tang goes all the way through the end of the butt cap and is peened over. The very end of the tang that fits into the butt cap might be threaded ( I'm guessing because is hexagonal like a nut) so that it can be tightened down to compress the leather washers that make up the handle. The way the tang is peened over looks a lot different from a traditionally peened tang so I'm guessing they have some special method they use to do that. It looks like it could have been done with a cold chisel. Again, all just a guess.
