Every gunsmith knows that the proper use of 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. Excessive headspace can be dangerous and negatively affect accuracy. For example, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust, which can be a serious safety hazard. Forster Headspace Gages are made with meticulous care and precise manufacturing standards to ensure accurate testing of your rifle's chamber. If a rifle closes on a NOGO gage, it suggests that the rifle chamber might have excessive headspace, which could compromise both safety and performance.