Every gunsmith knows 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 not only be dangerous but can also impair accuracy. For example, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust, creating a serious safety hazard. Forster Headspace Gages are crafted with meticulous care and stringent manufacturing standards to ensure precise testing of your rifle's chamber. If a rifle closes on a NOGO gage, it indicates that the rifle chamber might have excessive headspace, which could compromise safety and affect the rifle's performance.