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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 Headspace Gages 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).

  • 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 the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI), which sets 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. One should routinely check rifle chamber headspace every thousand rounds. If chamber headspace is excessive, the gun should be taken out of service until it has been inspected and repaired by a competent gunsmith.

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.


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.


Terminology: Headspace Clarification

In popular speech, “headspace” is used to describe three related measurements:

  1. Headspace GaugesThe Dimensions of the Cartridge Itself: Gun owners often refer to the “headspace” of the new or fired cartridge, whether or not it has been sized to specification.
  2. Headspace GaugesThe Dimensions of the Rifle Chamber: Additionally, gun owners will refer to the “headspace” of the chamber’s capacity.
  3. Headspace GaugesMeasuring 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 gage, and the gun’s actual chamber length , when the head of the cartridge is flush against the bolt face.
Ordering Information

Forster offers three lengths of headspace gages for most rifle calibers, 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 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.
  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 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 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 gages are slightly shorter than the SAAMI maximum in order to give a small safety margin.

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