RCBS Small Base Rifle Die Set -It consists of a Small Base Sizer with an Expander-Decapping Unit and Regular Seater Die with Seater Plug. The sizer resizes cases below SAAMI minimums, reducing the shoulder and body by a few thousandths. It also de-primes the case. The included Seater Die has a built-in roll crimper to secure the bullet at the same time it's seated. To seat bullets without crimping, simply unscrew the die until the crimp ring no longer engages the case mouth. Bottleneck type cases used in tight-chambering semi-automatic, pump or lever-action rifles; Includes small base sizer & seater dies;