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30 Cal Headspace gauges need help
I have three headspace gauges with the following measurments:
1.940
1.946
1.950
Does this represent no go, go, and field gauges?
Thanks in advance for the help.
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04-12-2009 10:28 PM
# ADS
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Mine are Forster 30-06, .270, 25-06
2.0487 = GO
2.0547 = NO-GO
2.0577 = FIELD
Bill Hollinger
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David,
I have a set of USGI 30.06 headspace gauges. They are marked the same as yours:
1.940 = Go Gauge
1.946 = No Go Gauge
1.950 = Field Gauge
Mike in NC
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Both Forster and Clymer use different datum points as reference. I would have the gauges you have checked to make sure the dimensions are still accurate.
I have a set of three Forster Gauges, and the gauges are marked with the dimensions as well as the type of gauge.
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The different numbers are because when the Army first adopted the .30-'03, rimless cartridges were new in the U.S. and no one quite knew how to measure headspace. So the Army set its headspace standards based on the case shoulder where it met the body of the case.
When SAAMI was established, they adopted the idea of setting standards based on a datum point ON the shoulder. (The point at which the diameter was a certain figure.)
So a GI GO gauge at 1.940 should be the same as a commercial spec GO gauge at 2.048. The gauge is the same, just a different measurement.
Jim
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I was wondering about mine. They're all Froster and marked 30/06, 270 and 25/06.
Go = 1.940"
No Go = 2.055"
Field = 2.0577"
Why such a spread between the Go and No Go? Different datum points?
sigman2
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Sigman2 - Based on what JimK stated it would appear to me that your Go gage is USGI spec, while the No-Go and Field are commercial spec., post SAAMI.
Difference between a 1.940" Go gage and a 1.946 No Go = .006 "
The difference between a commercial spec Go gage of 2.048 (same as USGI 1.940) and your 2.055" No Go gage would be .007 ".
Close enough for Govt. work I guess. This is just my take on what has been said, I don't know if I got this right or if I am even in the ball park,
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In spite of myth, magic and baloney regarding headspace, .001" (one thousandth of an inch) doesn't mean much.
Jim