Initially bullet molding blocks consisted of a single cavity for molding before WWI, after WWI emergence of dual/quadruple cavity blocks became popular with individual casters. Eventually sextuple cavity blocks for bullet molding came into play for law enforcement groups and shooting ranges. The bullet molds with 6 cavities were referred to as “Arsenal/Armory Moulds”

Single Bullet Mould

Arsenal/Armory Moulds (6 Cavity)

Initially bullet molding revolved around a base pour which would cause discrepancies in consistency with the base of the bullet, this resulted in unintended reductions in accuracy. Eventually Dr. Franklin Mann came up with the concept of a nose-pour which allowed the crafting of a base that would be more square to the launching chamber of the firearm in question.

Nose-Pour Mold

More Examples of Bullet Molding and Innovations: www.lasc.us/Fryxell_Book_Chapter_9_MouldsMouldDesign.htm