Every gunsmith knows that the proper use of 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 detrimental to accuracy. For instance, unsupported brass fired in a rifle with excessive headspace can rupture, causing gas to blow rearward like rocket exhaust. For your safety, Forster Headspace Gages are crafted with meticulous care and exacting standards to ensure precise testing of your rifle's chamber. If a rifle closes on a FIELD gage, it means the rifle chamber is dangerously close to or already exceeds the SAAMI specified maximum chamber size, emphasizing the critical importance of accurate headspace measurement for safe and reliable firearm operation.