Bringing the shotgun headspace to standard dimensions can reduce persisting misfires.

by Sergey Lyalko

Gunsmiths normally deal with headspace in rifles rather than shotguns. This is understandable since the shotgun is not so critical to accuracy and has lower chamber pressures. Normally, shotgun headspace is completely disregarded when diagnosing a misfiring gun. Three things a gunsmith needs to identify in a failing shotgun are insufficient firing pin strike, bad shotshells, and if there is excessive distance between the primer and the breechface of the gun.

For this article we’ll assume the shotgun has a firing pin with normal length (1.5-1.8mm) that strikes hard enough and that the ammunition is within specifications. That leaves us with excessive distance between primer and breechface, which is an excessive headspace.

The sketch here shows the rim recess and relation between rear edge of the chamber and the face of the action. In the United States, chamber rim recess dimensions are specified by SAAMI as the…

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