I´ve been watching videos on how to make boolits molds; I´ve seen they use self centering vises but can´t understand how the halves of the mold are held in place, it looks like they are pinned by steel rods..I can´t really see (understand) how its done, why not simply bolt the halves to the vise jaws? I´m not talking about the alignment pins but the way the mold is held in place during milling
https://www.youtube.com/watch?v=m1YPTarNliw
https://www.youtube.com/watch?v=2ERbCJG5tD8