Now I wonder where you got that idea.
The cone shape is easy if you have a hand motor drill and a drill press; put your piece in the drill press take a cone shaped grinding wheel and put it in you drill motor [hand ] make an upright for your drill press and strap your drill motor to it. If you position your drill motor right then when you bring the head of the drill press down it will grind a nice round cone shape.
It really gives you a lot more options with the PB's. Lee
P.S. if you want to make a high BC version use a brass bolt and cone the head so the edge stops just short of the curve of the shoulder .