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Case Gauges & Headspace Tools

In firearms, headspace is the distance measured from a closed chamber's breech face to the chamber feature that limits the insertion depth of a cartridge placed in it. The exact part of the cartridge that seats against the limiting chamber feature varies among cartridge and gun designs. Bottleneck rifle cartridges headspace on their case shoulders; rimmed cartridges headspace on the forward surfaces of their case rims; belted cartridges headspace on the forward surfaces of their case belts; rimless pistol cartridges headspace on their case mouths.

When headspace is larger than the cartridge case, there is room for front-to-back cartridge movement when the breech of the gun is closed. Excessive head clearance is undesirable for several reasons. It can allow a cartridge's primer to slide beyond the reach of the firing pin to adequately indent the primer to achieve reliable ignition (though extractor hooks may act prevent the cartridge moving forward in this situation).

In chamber designs that don't fully support the case head, it can allow a case to expand excessively, which can contribute to thinning or even split the brass. Thus the cartridge can rupture rearward, which risks releasing hot gases under high pressure that can damage the firearm and cause injury.

If a chamber's headspace is too short, the gun may not close and lock completely, preventing firing.

  • RCBS Precision Mic

    £100.50

    A few twists of the Precision Mic and you'll know your chamber headspace and bullet seating depth to 0.001 of an inch. The Precision Mic measures f...

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    £100.50