Every gunsmith understands that the proper use of a headspace gage is the most reliable method 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 not only impair accuracy but also pose a serious safety risk. For example, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward with explosive force, much like rocket exhaust. For your safety, Forster Headspace Gages are crafted with precision and exacting standards to ensure accurate testing of your rifle's chamber. If a rifle closes on a FIELD gage, it indicates that the chamber is dangerously close to or has already exceeded the SAAMI specified maximum chamber size, emphasizing the critical need for proper headspace measurement.