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Right in part only. The gauge numbers did not indicate the groove diameter, but a diameter between the lands only. It was measured at the proofhouse using cylindrical plugs. The largest number that passed the barrel was stamped. There were no intermediate steps from gauge number to gauge number. Here a # 156.14 = 7.87 mm = .310" plug passed the barrel. but a # 141.96 = 8.13 mm = .320" one did not. So the actual bore/land diameter of a Barrel marked 156.14 may have been as large as 8.12 mm = .319".

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