.30-06 Headspace Go Gauge
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's 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. Although the GO gauge is necessary for a gunsmith or armorer, it usually has fewer applications for the collector or surplus firearms purchaser.
.30-06 Springfield headspace gauges are usable in .25-06, .270 Winchester, 6.5-06, 8mm-06, .338-06, and .35 Whelen chambers.