RIMLESS CARTRIDGE HEADSPACE: The proper use of Headspace Gauges is the most reliable way to test rifle chamber length. Headspace in a rimless cartridge is the distance between the bolt face and a datum line, determined by SAAMI, where the front of the cartridge rests on its shoulder when the bolt is closed.
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.
PRECISION MACHINED: Manufactured from top-quality, hardened steel and precision ground to ANSI and SAAMI tolerances. Headspace tolerance ground to a very exacting +/-.00015. Each Headspace Gauge thoroughly inspected with NIST-certified measurement tools to ensure the highest quality product.
MEASURING MEANINGFUL HEADSPACE: Properly speaking, and for safety purposes, one measures “headspace” as the difference between the length of a standard cartridge, as represented by a Gauge, and the gun’s actual chamber length , when the head of the cartridge is flush against the bolt face.