Full length die sets are for bottleneck rifle and pistol cases, and they include a full length sizing die and a seater die. The full length die will bump the shoulder of the case to extent the die is adjusted up or down in the press. We suggest using a cartridge headspace gage tool to get the correct shoulder bump. The full length die also sizes the body of the case so it will chamber easily for the next firing, then the die decaps the spent primer. The expander ball passes through the neck of the case and sizes the neck to the correct tension. Cases must be lubricated before full length sizing.
The RCBS seater dies for bottleneck cases will seat bullets correctly in full length sized cases or neck sized cases. These seater dies have a built-in crimp ring to enable you to crimp the case into the bullet if you wish to. The seater die is easily adjusted to crimp or not to crimp by raising or lowering the die position in the press.
Full length 2 die sets are the basic building block of the reloading process. Many shooters wear out multiple barrels or rifles using just one full length reloading die set. We recommend that new reloaders start with a full length die set and learn how to set the dies up correctly before they jump in to other types of reloading dies.
Big Book Catalog, Issue:68, Page:535
Sinclair, Issue:5B, Page:055