Every gunsmith understands that the proper use of a headspace gage is the most reliable way to test the length of a rifle chamber. "Headspace" refers to the distance between the face of the breech and the base of the cartridge when the action is closed. Excessive headspace can be dangerous and impair accuracy. For instance unsupported brass fired in a rifle with excessive headspace can rupture causing gas to blow rearward like rocket exhaust creating a serious safety risk. Forster Headspace Gages are manufactured with meticulous care and strict standards to ensure precise testing of your rifle's chamber. If a rifle closes on a NOGO gage it indicates that the rifle chamber may have excessive headspace which could compromise both safety and performance.