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. Excessive headspace can be dangerous and can also impair accuracy. For example, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust, which poses a significant safety risk. Forster Headspace Gages are crafted with precise care and strict manufacturing standards to ensure accurate testing of your rifle's chamber. If a rifle closes on a NOGO gage, it indicates that the rifle chamber might have excessive headspace, which could compromise safety and performance.