The Lee Precision Breech Lock Challenger Press is an O frame press. The O frame press by design is the strongest and by far the most popular style press. The larger than average opening allows for maximum hand clearance. The spent primer catcher is positive and allows you to route the spent primers directly to the trash can. Priming is a dream with the Lee Lever Prime System. Best of all, it includes the Breech Lock Quick Change die system. Change dies instantly with a twist of the wrist, and you never have to re-adjust your die.