The RCBS Competition Dies are for the competitive marksman that measures success in fractions of an inch.
The Competition Seater Die has a micrometer adjustable, free floating and self centering bullet seating system with convenient bullet loading window. Bullet seating depths are adjustable to .001". An extended shell holder is included for shorter cartridges. Dies have a durable black oxide finish. Not for use with progressive reloading presses.
Big Book Catalog, Issue:68, Page:533
Sinclair, Issue:5B, Page:054