Austin Hogan published data on this a long time ago. As with most of his research (choke shapes, french polish, etc.) it was so informative that I copied it to my Parker files so that it survived to my posterity. I am attaching it. Bottom line is prior to s/n 70,000, 12 ga bores were commonly in the .755 range, while afterward they tended to conform to the .730 range. Enjoy
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