The RCBS Competition Dies are for the competitive marksman that measures success in fractions of an inch.
The Competition Full Length Die features a raised expander ball allowing extra leverage for smooth, effortless neck expansion. This enables maximum concentricity between the neck and body of your case. Dies have a durable black oxide finish. Not for use with progressive reloading presses.
Big Book Catalog, Issue:66, Page:514
Sinclair, Issue:3B, Page:061