I use screws though I have not made a lot of these but this was one of my early forge projects too many years ago
Screw them together or rivet.
Put some brass scraps and borax in the cavity and put the buttplate "point" down in the fire and heat. The coal will help hold the parts together and it does not take a great deal of time if the fire is good. The brass may even show where it has flowed into the screw threads. Let it cool a little before taking it out of the fire so the joint can set. Pulling it out hot can cause the parts to move.
Making the parts and filing for a good fit is far harder than the brazing.
Some folks cheat and weld them at the tip rather than screws or rivets.
Just make sure the screw is actually steel.
Don't ask how I figured this out
Dan