The Dillon Precision Accurized Micrometer Bullet Seating Die is built for a bullet diameter, and expands with a conversion rather than a second die. For a handloader who shoots more than one cartridge in a family - and most of us do - that changes the shape of the whole purchase. These conversion kits are available in all popular bullet calibers to save you money over having to buy a whole new seating die for every cartridge.