Every gunsmith knows that using a headspace gage is the most reliable method for testing 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 and excessive headspace can be both dangerous and impair accuracy. For example, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust, which presents a significant safety risk. Forster Headspace Gages are crafted with meticulous care and strict manufacturing standards to ensure accurate 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 can compromise both safety and performance.