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" is 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 instance, unsupported brass fired in a rifle with excessive headspace can rupture, allowing gas to blow rearward like rocket exhaust, posing a serious safety risk. 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 suggests that the rifle chamber may have excessive headspace, which could compromise both safety and performance.