I know some will cringe at this, but a hacksaw works just fine. Flat file to clean it up, file and sandpaper a nice radius on the outer edge, then a round head screw and lapping compound on a drill for the crown. Hit it with some cold blue and you're done. Take your time and it looks professional.
I like 18", any less looks funny to me.
Larry Potterfield, the owner of Midway USA, has videos on Youtube showing it done.