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Posted: 1/13/2005 7:02:04 AM EDT
[Last Edit: 1/13/2005 7:10:57 AM EDT by JHaines]
I'm looking to get a headspace guage for some of my C&R rifles to guarantee that they are safe to shoot.

The choices are from Brownells are:

"Go" guage
"No Go" guage
"Field" guage

Which one would I need, and what is the difference ?

Thanks!
Link Posted: 1/13/2005 7:08:20 AM EDT
For your stated purpose, the "Field Gauge" would be the better choice.

Mike
Link Posted: 1/13/2005 7:11:11 AM EDT
Ditto what Mr Wilson said.

Here's a bit of info on "headspace"...

hybrid.ualr.edu/satu/headspace.html
Link Posted: 1/13/2005 7:14:34 AM EDT
where can you get them for a good price?
Link Posted: 1/13/2005 7:19:40 AM EDT
Brownells has various gauges for about $30.

Thanks for the link on headspace. Great info.

From what that link seems to indicate, you don't have to break down the
bolt on a Mauser 98 to check it with a 'no-go' or 'field' gauge. At the last
gunshow I went to, a gentleman broke down the bolt and removed the
firing pin from a K98 to check the headspace. Any idea which one is
correct (i.e. - did the guy at the gun show know what he was doing, or
was he just uninformed) ?

Thanks!
Link Posted: 1/13/2005 7:26:37 AM EDT

Originally Posted By JHaines:
I'm looking to get a headspace guage for some of my C&R rifles to guarantee that they are safe to shoot.

The choices are from Brownells are:

"Go" guage
"No Go" guage
"Field" guage

Which one would I need, and what is the difference ?

Thanks!



For rimmed cartridges, headspace is measured by the thickness of the rim. For rimless, it's the distince between some point on the shoulder to the base of the cartridge. A .303 guage is a tiny little thing looking like the last 3/4 inch of a cartridge, where a 7.62*51 guage looks like a cartridge with the very tip missing.

The Go is the shortest, followed by the No Go, followed by the Field. In laymans terms, it's how far the bolt holds the cartridge into the chamber. If it holds it too far out, you can suffer from a ruptured case because the steel of the barrel is not 'containing' the cartridge properly. The brass of a cartridge is like a play dough viscosity sealant at those temps and pressures. The base can handle it temporarily, but the thin walled part demands support from the chamber. If it's not in there correctly, you can suffer from a blowout.

Your bolt should close on a GO guage. If not, the headspace is too small. Ergo, the chamber is too shallow and needs reaming, or the bolt is too long. Generally, this will be an obvious problem as the bolt will never close correctly. If it closes under pressure, the biggest danger is that during use it may not close fully, and may fire under a partially closed condition. Not good.

Your bolt shoud not fully close on a No Go guage. If it closes on the go, and not on the No Go, you're in excellent shape. You are in SAAMI spec.

Your bolt should not fully close on a Field guage. If it didn't on a No Go, it has no chance on a Field. Use a Field when it closes on a No Go to see how bad you are off spec. Basically, the distance between Field and No Go represents a buffer area where if you are shooting new brass, it can probably take the excessive stretching without a problem. However, the brass gets badly mangled in doing so, although this won't be apparent to you. If this brass is reloaded and shot in the same gun a second time, you may get a blown case.

Beyond the Field guage, your chances of a burst cartridge go up quickly.


Link Posted: 1/13/2005 7:26:44 AM EDT
To get a true reading the bolt need to be broken down. Firing pin/cocking assy and extracter need to be removed from the bolt. DO NOT FORCE THE BOLT CLOSED while the gauge is in It will damage the chamber and or the gauge.
Link Posted: 1/13/2005 7:29:12 AM EDT

Originally Posted By JHaines:
Brownells has various gauges for about $30.

Thanks for the link on headspace. Great info.

From what that link seems to indicate, you don't have to break down the
bolt on a Mauser 98 to check it with a 'no-go' or 'field' gauge. At the last
gunshow I went to, a gentleman broke down the bolt and removed the
firing pin from a K98 to check the headspace. Any idea which one is
correct (i.e. - did the guy at the gun show know what he was doing, or
was he just uninformed) ?

Thanks!




The bolt does not need to be stripped on a Mauser to check HS. The gauge is counterbored to clear firing pin and base is cut to clear extractor. You will need to develop a "feel" to correctly use the gauge tho. Remember you are trying to measure the HS not attempting to close the bolt on the gauge. A little practice is all it takes.

Brownells and Midway is where I have got all mine from.
Link Posted: 1/13/2005 10:54:25 AM EDT
Thanks for the information folks!
Link Posted: 1/13/2005 3:55:50 PM EDT
While I believe military 5.56 gauges have a cut out for the extractor and ejector, my Forster gauges do not have any cut outs other than a blind hole for the firing pin.

FWIW, Brownells sells Forster headspace gauges for $21.40 retail, $14.60 dealer.

Below are the results of excessive headspace in a Lee-Enfield. The left photo shows a total head separation, the other photo shows an incipient crack in a fired case.



I got a face full of gunpowder when I fired the round on left!
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