British guns built for sale in America (later ones anyway) were usually originally chambered 2.75". I have a Webley&Scott Model 700 16ga imported by Abercrombie&Fitch back in the early '60s with original 2 3/4" chambers. It also has matching hairline cracks in the stock behind the frame indicating to me that an owner along the way shot 'high brass' American 16ga loads in it...Geo