The Forster Datum Dial Ammunition Measurement System gives you the data you need to refine your case sizing operations. Includes one Datum Dial tool for checking cartridge cases, chart showing common datum diameters, instructions and storage box. A user supplied caliper is required. A bullet dial must be purchased as well to measure the overall length to the bullet ogive. The Datum Dial provides a relative measurement between the base of a case to a datum point on its shoulder angle. It may be used before sizing operations to find the optimal headspace for your firearm. After sizing operations, use the Datum Dial to check the setup and consistency of your reloading process. FeaturesBetter accuracy because your ammunition's headspace is tailored to your firearms' chamberSafer shooting because excessive headspace, which may lead to dangerous case separation, can be avoidedQuick sorting of batches of cases, bullets and cartridges to effectively remove variation to provide r...