Every gunsmith knows that using 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 affect 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 crafted with meticulous care and exacting manufacturing standards to ensure precise testing of your rifle's chamber. If a rifle closes on a NOGO gage, it may indicate that the rifle chamber has excessive headspace, which could compromise safety and performance.