I have old American doubles with bores all over the place. On the loose side I have an 1889 12-gauge Parker Bros. that has bores .757", and I have my Father's old 1896 vintage Remington AE-Grade that has bores .744". On the tight side I have a Baker $100 Pigeon Gun 10-gauge with bores .750" and my Fox Gun Co., Balto., MD., U.S.A. 12-gauge has a right bore of .712" and a left bore of .708"?!?