British, Birmingham proof, proof marks are not for nitro, and nothing to suggest that they are 2 3/4" either I can see a 3/4 in the photo of the forend retaining iron; has the "2" in the 2 3/4 been cut off?
That 2 on the rib at the muzzle is intriguing...
Nice old gun though... make a good one for ducks with lead when we get a decent season again. $500-$750ish in the current market, depending on a closer inspection with bore and wall gauges.

Last edited by cadet; 12/28/15 12:29 AM.