The Redding Instant Indicator Comparator is useful for quickly comparing headspace and bullet seating depths within 0.001 of an inch. The headspace measurement is from the case shoulder to the base. This information is critical for setting the sizing die to achieve the precise amount of shoulder bump. To compare bullet seating depths simply insert a standard Redding sizing bushing of the proper bore diameter for the caliber you are using. Supplied with instructions to check and quickly compare overall case lengths and bullet base to ogive. One bore diameter bushing is included (as indicated). Technical Information Fits: The Instant Indicator fits the cartridge listed in the description, however it may be used for a family of cartridges with the same shoulder angle Function: Check headspace from the case shoulder to the base of the case Notes: Information provided by this indicator is useful for setting up sizing die to achieve the precise amount of shoulder bump Indicator is supplied with instructions and requires the use Redding Neck Bushings (One is included for the appropriate cartridge)