Lee Factory Crimp Die crimps your bullets in place the same as factory ammo. A collet gently, but firmly squeezes the very end of the case into the crimping groove, exactly the same as factory ammo. Lee 243 WSSM Factory Crimp Die crimps the bullet in place more firmly than any other tool. Tests demonstrate that even bullets which have no crimp groove will shoot more accurately. A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move. This higher start pressure insures a more uniform pressure curve and less velocity variation. Features: Gives a segmented straight crimp, and crimps more firmly than any other tool It is impossible to buckle the case as with regular roll crimp dies Necessary for hunting and combat, ammunition will be more accurate and better able to withstand rough handling because the bullet is firmly crimped in place Tests demonstrate that even bullets with no cannelure will shoot more accurately if crimped in place with the Lee factory crimp die A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move This higher start pressure insures a more uniform pressure curve and less velocity variation Even powder selection is less critical, until now, handloaders seated the bullet to touch the rifling to achieve similar results, this is not always possible nor desirable