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Headspace GagesDownload product-specific catalog information (accompanying PDF format)

Exclusive Forster quality offers the best way to check your rifle chamber for safety.

Your safety and performance are on the line. Improper headspace may be dangerous to the shooter as well as an impairment to accuracy. The proper use of a Headspace Gage is the most reliable way to test the length of a rifle chamber. Excessive headspace may lead to gas leakage around the case or head separation and the sudden release of high pressure gas. Insufficient or excessively tight headspace may cause malfunctions such as failure to lock. It often makes extraction difficult and may cause dangerous stresses on the mechanism, which may, in turn, shorten component life expectancy or lead to failure.

  • Headspace GaugesLarge caliber selection of both rimmed/belted and rimless gages
  • Three lengths of Headspace Gages for most rifle calibers offered (GO, NO-GO, FIELD).
  • Full sets for three calibers (223, 308 and 30-06). Each set contains 11 gages, clearly marked in .001” increments from shortest SAAMI length to longest SAAMI length.
  • Manufactured from top-quality, hardened steel and precision ground to ANSI and SAAMI tolerances.
  • Headspace tolerance ground to a very exacting ±.00015″.
  • Each Headspace Gage thoroughly inspected with NIST-certified measurement tools.
Choosing the Correct Gage

According to SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute), who set product standards for firearms and ammunition, headspace is “The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. Some shooters are under the misconception that headspace is fixed over the life of the firearm. Headspace can increase after repeated use of ammunition that causes too much pressure. Handloaders should routinely check rifle chamber headspace every thousand rounds.

Headspace is measured differently, depending on whether the firearm’s caliber uses rimmed, belted or rimless cartridges.

Rimmed and Belted Cartridges
Headspace = distance between the bolt face and the top of the rim (chamber face) when the bolt is closed.

Headspace_1_lg

Rimless Cartridge
Headspace = 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.

Headspace_2_lg

Ordering Information
Forster offers three lengths of headspace gages per rifle caliber, in order from shortest to longest:

  1. GO: Corresponds to the minimum chamber dimensions. If a rifle closes on a GO gage, the chamber will accept ammunition that is made to SAAMI’s maximum specifications. The GO gage 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 gage 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 gage, 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 gage is a valuable tool for checking a newly-reamed chamber in order to ensure a tight and accurate chamber.
  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’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 gages are slightly shorter than the SAAMI maximum in order to give a small safety margin.

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