Rocketman--Sorry. Yes, meant that for you. Thanks for responding. My Model 400 Grade 1 dates from 1924, It does have 2 3/4" chambers which appear to be original. Can't see any indication they've been lengthened. But chamber length was not required as a proofmark until 1925, so not marked that way.

If Tom responds to my post and checks out the Hill Rod & Gun website, we'll know whether he has a Model 400 Grade 1. Has a lot of bells and whistles not found on basic boxlocks, and absolutely incredible small scroll engraving.