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 both 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 is a serious safety hazard. Forster Headspace Gages are carefully manufactured to exacting standards, ensuring accurate testing of your rifle's chamber. If a rifle closes on a GO gage, it confirms that the chamber will accept any ammunition made within SAAMI (industry standard) specifications, ensuring safety and optimal performance.