30-06 headspace gauge help

[pcaru1]

Can someone help with an ID of these gauges. Are these min (1.940) and max (1.946) gauges military? I own a Forster No-Go (2.0547) and a field (2.0577). what is the difference and is the difference important?

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[Kirk]

I'm not a machinist or gun smith so I can't say one is better than the other but I do know that different makers use different datum points for their measurements. That's why the numbers differ - they measured to different points.

[pcaru1]

Maybe these are measured to the shoulder instead of the datum line?

Would the max one be a No-Go or a field?

[purple]

The pic shows commercial gauges. Military gauges will be marked with drawing numbers and have the head cut out to accomodate the M1 Garand ejector, so that the bolt doesn't have to be dismantled to check headspace. There were/are 3 diffeerent headspace gauges for the .30-06 as follows:
1. 1.940 minimum or "go" gauge. Bolts are to close w/o resistance.
2. 1.946 maximum or "no-go" gauge. Bolts are not to close on this gauge when rifles are re-barreled.
3. 1.950 reject or "field" gauge. Bolts in rifles in service are not to close on this gauge. If they do the rifle is withdrawn from use.
I own all of GI, Clymer and Forster gauges. All are good/safe to use,
but there are slight differences among them. I have found that the Clymer "no-go" is quite close to the Forster "field" gauge while the Forster "go" gauge is slightly different than the GI "go" gauge. This was a frequently discussed topic on the old CSP forum where Mr. Gus Fisher, a retired USMC armorer, cited that the Clymer gauges were tested and found closer to spec. The CMP was using Clymer gauges to check rifles and the consensus was that the Clymer "no-go" gauge would pass more rifles on the maximum headspace check. The key thing is not to mix brands. If you use a Forster "go" gauge, then also use a Forster "no-go" gauge.

[Parashooter]

The gauges in pcaru1's picture are Wilson (commercial) gauges that are marked with military-style dimensions. His Forster gauges are marked according to the commercial style (head to .375" datum line). It appears that Forster has chosen a "Field" dimension .001" shorter than the SAAMI maximum of 2.0587", demonstrating the subjectivity of such terms as "No-Go" and "Field".

[gulliver62]

I would only add that there are additional commercial gauges available that are graduated between the go and no-go. These are used to cut the chamber to a more specific size when installing a new barrel. These are what was used installing the new barrel on my match Garand.