338 Remington Ultra Magnum (RUM) Ackley Improved Headspace Gauge

Pacific Tool and Gauge offers five lengths of headspace gauges per rifle caliber on chambers listed by both SAAMI and CIP. In order from the shortest to longest, they are: GO/CIP-MIN, CIP-MAX, NO-GO, and FIELD. 0.0005" tolerance

1. SAAMI 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.
2. NO-GO: Corresponds to the maximum headspace Forster recommends 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 gauge. The NO-GO gauge is a valuable tool for checking a newly-reamed chamber in order to ensure a tight and accurate chamber.
3. SAAMI FIELD: Corresponds to the longest safe headspace. If a rifle closes on a FIELD gauge, its chamber is dangerously close to, or longer than, SAAMI’s 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.
4. CIP Min: Corresponds to CIP minimum chamber dimensions.
5. CIP Max: Corresponds to the CIP maximum chamber dimensions.

Cross-compatibility: Many of our headspace gauges are compatible with multiple chamber specifications. For instance, .30-06 Springfield headspace gauges are usable in .25-06, .270 Winchester, 6.5-06, 8mm-06, .338-06, and .35 Whelen chambers. We list known compatible chambers with each headspace gauge product. Refer to our Compatible Headspace Gauge Chart below or ask your sales representative if your gauge is cross-compatible.

Our chart is available here: Headspace Compatible Chart