Every gunsmith understands that the proper use of a headspace gage is the most reliable way to test 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 and excessive headspace can be both dangerous and detrimental to 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 concern. Forster Headspace Gages are manufactured with meticulous care and stringent 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 ammunition made within SAAMI (industry standard) specifications, offering peace of mind regarding safety and performance.