Lee Large series (1 1/4x12 thread) 50 BMG Factory Crimp Die, used with the Classic Cast Press only, 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.