Every gunsmith knows that proper use of a headspace gage is the most reliable method 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 can impair accuracy. For example, unsupported brass fired in a rifle with excessive headspace can rupture, allowing gas to blow rearward like rocket exhaust, which is a serious safety risk. Forster Headspace Gages are manufactured with meticulous care and exacting 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.