Every gunsmith knows that proper use of a headspace gauge 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 dangerous as well as impair accuracy. For instance, unsupported brass fired in a rifle action with excessive headspace can rupture, allowing gas to blow rearward like rocket exhaust. Because your safety is on the line, Forster Headspace Gauges are made with painstaking care and exacting manufacturing standards to ensure accurate testing of your rifle’s chamber.

Forster Products offers three lengths of headspace gauges per rifle caliber. In order from the shortest to longest, they are GO, NO-GO, and FIELD:

1. GO: Corresponds to the minimum chamber dimensions. If a rifle closes on a GO gauge, the chamber will accept ammunition that is made to SAAMI maximum specifications. The GO gauge is essential for checking a newly-reamed chamber in order to ensure a tight, accurate, and safe chamber that will accept SAAMI maximum ammo.

2. NO-GO: Corresponds to the maximum headspace we recommend for gunsmiths’ chambering new bolt-action rifles. This is not a SAAMI-maximum measurement. If a rifle closes on a NO-GO gauge, it may still be within SAAMI specifications, or it may have excessive headspace. To determine if there is excessive headspace, the chamber should then be checked with a FIELD gage. The NO-GO gauge is a valuable tool for gunsmiths’ reaming new chambers, in order to ensure tight and accurate headspace.

3. FIELD: Corresponds to the longest safe headspace. If a rifle closes on a FIELD gage, its chamber is dangerously close to, or longer than, SAAMI-specified maximum chamber size. If chamber headspace is excessive, the gun should be taken out of service until it has been inspected and repaired by a competent gunsmith. FIELD gauges are slightly shorter than the SAAMI maximum in order to give a small safety margin.