Diagram of .308W & 7.62mm headspace gauge datums?

[enscien]

The 0.400 datum diameter I quoted for UK military 7.62mm NATO weapons and ammunition is taken from the NATO standardisation drawings which were based on the original American design. All NATO countries may be expected to use this for military purposes but as Peter says, will have different headspace criteria for different weapons.
Dimensions for the .308" Winchester chamber and cartridges are given in SAAMI drawings published in the American NRA 'Handloading' manual and also use the same .400" diameter datum. Limits of 1.640/1.630" are given for the weapon, and 1.634"-.007" for the cartridges. Interestingly this datum is not reproduced in the Imternational CIP tables (Table I) for .308" Winchester.

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[Thunderbox]

The 0.400 datum diameter I quoted for UK military 7.62mm NATO weapons and ammunition is taken from the NATO standardisation drawings which were based on the original American design. All NATO countries may be expected to use this for military purposes but as Peter says, will have different headspace criteria for different weapons.
Dimensions for the .308" Winchester chamber and cartridges are given in SAAMI drawings published in the American NRA 'Handloading' manual and also use the same .400" diameter datum. Limits of 1.640/1.630" are given for the weapon, and 1.634"-.007" for the cartridges. Interestingly this datum is not reproduced in the Imternational CIP tables (Table I) for .308" Winchester.

I thought that it was this 0.4" datum that differed between 7.62mm and .308W, hence the difference in length between 7.62mm and .308W headspace gauges that are nominally of the same length?