Agree with Rocketman that there is no longer any prejudice against 2 1/2" guns in the States, at least not among knowledgeable doublegun fans. If you attend any of the big side by side shoots, you'll likely see more old, short-chambered guns than modern ones. And all kinds of people shooting 2 1/2" shells. In fact, a fine British or European double that has had its chambers lengthened from 2 1/2" to 2 3/4" without proper reproof is the gun that will suffer in value upon resale.
Re what the Brits shoot . . . it's not quite as clear as "only 2 1/2" shells in 2 1/2" guns". 67/67.5MM shells approved for use in 2 1/2" guns, and so marked on the cartridge boxes, are quite common in the UK and Europe. Some of these shells have a fired length as long as some of our nominal 2 3/4" shells (depends on which of theirs compared to which of ours). It's not the case length that's the major factor, but rather the load: pressure, shot charge, velocity.
