Every gunsmith understands 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 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, creating a serious safety risk. Forster Headspace Gages are crafted with great care and strict manufacturing standards to ensure accurate testing of your rifle's chamber. If a rifle closes on a GO gage, it confirms that the chamber will safely accept any ammunition manufactured to SAAMI (industry standard) specifications, ensuring both safety and reliability.