Forster Headspace Gages (Gauges)

Refer to this table to determine which rifle chambers may be inspected with a given Forster gage.

Contact us with inquiries for special gages.

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Why Choose Forster Headspace Gages?

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. Forster Headspace Gages are made to exacting manufacturing standards to ensure accurate testing of your rifle’s chamber. Smart gunsmiths, shooters and reloaders select Forster’s Headspace Gages because:

  • We offer a large caliber selection of both Rimmed or Belted Gages (Gauges) and Rimless Gages (Gauges).
  • See our Headspace Gage (Gauge) to Caliber Interchangeability Tables.
  • We offer:
    • 11 pc Headspace Gage (Gauge) Sets
    • NATO Chamber Headspace Gages (Gauges)
    • 8mm Mauser Chamber Headspace Gages (Gauges).
  • We offer three lengths of Headspace Gages per rifle caliber.
  • Headspace tolerance is ground to a very exacting ± 0.00015 in.
  • Every headspace gage is thoroughly inspected.
  • Forster Products has over 75 years of manufacturing experience and their quality system is certified to the ISO9001 Quality Standard. With something as critical as Headspace Gages, we leave nothing to chance.

Choosing the Correct Gage (Gauge)
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

Forster offers three lengths of headspace gages per rifle caliber. In order from the shortest to longest, they are: GO, NO-GO and FIELD:

  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.