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. Excessive headspace can be dangerous and can impair accuracy. For instance, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust, which poses a serious safety risk. Forster Headspace Gages are crafted with meticulous care and strict manufacturing standards to ensure precise testing of your rifle's chamber. If a rifle closes on a GO gage, it confirms that the chamber will safely accept any ammunition made within SAAMI (industry standard) specifications, ensuring both safety and reliable performance.