In my collection of American doubles, I have 12-gauge guns with bores as tight as .708" (Fox Gun Co., Balto., MD., U.S.A.) to an 1889 vintage Parker Bros. with bores of .757". I've also got a 10-gauge Baker $100 Pigeon Gun with bores of .750". A lot of trap shooters shoot Stan Baker "Big Bore" barrels that are .800" all the way to the choke.