These micrometer cartridge headspace tools will enable you to set up full length sizing dies for the precise amount of shoulder bump you wish. Precision Mic gages are initially calibrated on a once-fired case, and the micrometer will read shoulder set back variation from initial set-up. Each Precision Mic kit also includes a bullet seating depth tool for initial seater die set-up.
Big Book Catalog, Issue:66, Page:514
Sinclair, Issue:3B, Page:042