Head Spacing

Checking Headspace with a Field Guage

(text and photos extracted from a tutorial created by bunkysdad, Administrator,

The definition of headspace when dealing with rimmed cartridge rifles like the Mosin Nagant or Lee Enfield is simply the space allowed in a rifle or pistol for the rim of the cartridge. Too small, and the bolt won't close. Too large, and the case may stretch or allow hot gases to unsafely leak into the chamber. While there are other types of headspace guage tools available, the disc type headspace guage fits easily on the bolt head without removing the extractor. This is a very nice feature that makes a headspace check about a one minute process.

For the sake of illustration, I placed the bolt in a soft-jawed vise so you can see where the tool fits. The guages are available in a go-guage, a no-go guage,and a field guage. This illustration is being conducted with a field guage, which is considered the largest amount of headspace that is still considered safe to fire. The tool used is available from Okie Headspace Guages. They can be found on the header area of this forum, as they are a sponsor of the Russian Mosin Nagant Forum.

The tool is a precision ground coin like disc notched to clear the extractor.

With rifle held vertically, place the disc on the bolt head and seat it flatly with the notch clearing the extractor. It will lay completely flat if it is positioned correctly.

If the bolt will not close when applying gentle pressure the rifle passes the field guage test.

The Headspace test would be the same with a tighter tolerance no-go guage.

Choosing a No-Go gauge or a Field Guage is a matter of preference. A go-guage is not normally needed except perhaps by a gunsmith while installing a new barrel or making extreme repairs.

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