Whidden Case Gauges can be used to determine your own rifle's headspace and whether or not it falls within SAAMI specifications. Additionally they can be used to determine the headspace of factory ammunition or hand loads and see how they compare with your own chamber. The Case Gauge can also give you information on how to adjust your resizing die to give the optimum amount of shoulder setback during sizing. Case Gauges feature all stainless steel construction. They have easy to read markings and they are calibrated using actual Pacific Tool & Gauge headspace gauges. Mfg: Whidden Gunworks