Small Base Sizer Dies are usually required for reloading ammunition to be used in automatic, semi-automatic, pump, slide and some lever-action rifles. These dies size the body of cases somewhat smaller in diameter and also set the shoulder back slightly more than a Full-Length Sizer Die to ensure proper functioning in the actions of these rifles. Small Base Die Sets not recommended for ammunition used in bolt-action rifles. Small Base Set contains Small Base Sizer with ExpanderDecapping Unit and Regular Seater Die with Seater Plug. Mfg: Rcbs