I have a Ca 1902 12ga sidelock VL&D/J P Sauer & Son "Knockabout" with 2 3/4" chambers. With the VL&D connection & the "Son" spelling it was definitely built for export to the US. It has the 12 in a circle marking & the face of the extractors are stamped 70.
I believe the key here is if it has only the chamber mark of gauge in a circle with no additional marks it is reasonably safe to assume it was chambered for the "Standard" shell. For continental guns this would have been 65mm (approx 2 9/16"). Also many "So Called" British nominal 2˝" guns seem to have chambers running from 65mm-67mm (2 9/16"-2 5/8").
