Extra powder dies allow you to move your powder measure from toolhead to toolhead without changing the "belling" adjustment. TOOLHEAD NOT INCLUDED.
The XL powder die is necessary for the larger diameter cases, including 500 S&W, 50 AE, the WSM and WSSM family of cartridges, the RUM and RSAUM family of cartridges, .378 Weatherby and up, .338 Lapua, and 416 Rigby.