Checking Headspace with a Field Guage
(text and photos
extracted from a tutorial created by
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
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.