Dr. Tim, I think the parallel sided tip probably came about when precision rolled stock and the screw-machine were fully developed. I would guess Dixie Gun Works invented it!
I make my tips out of rolled sheet steel, with an 8-32 nut brazed in at the end. I shape the rod to have a flared tulip at the other end.Invaluable tool for tapering a ramrod: http://thosmachine.wordpress.com/2009/07/19/ramrod-scraper/ ..........another shameless plug