Well Ted . . . a lot more Darnes were made than just ONE model Webley & Scott. And those Scotts had an American importer for most of the period following the 1954 proof laws. So certainly the ones coming to this country would have had 2 3/4" chambers. Earlier ones (but they didn't appear until a couple years after the war) did have 2 1/2" chambers. Problems? Never had one with a 700 series gun. They're pretty reliable . . . although, as you've noted, they don't have disc-set strikers. My Model 400 does.

And I'm pretty sure you're mistaken on Boothroyd and the proofmarks. Those are standard proofs under the law of 1925. I've never read anyone who said BSA was out of the gun business prior to 1925.