The lettre annale is a 'g' for 1928
Cornell Pubs has an A&F 1929 catalog but it may not have been an A&F gun. The ones I've seen had the chamber length indicated in inches.
This one has FOR ABERCROMBIE & FITCH CO. on the R barrel
https://www.rockislandauction.com/detail/48/1616/cased-dumoulin-box-lock-model-double-barrel-shotgun
https://cornellpubs.com/product/874/

The tubes are fluid steel by Laurent Lochet-Habran and are Smokeless Powder proved, which was mandatory after 1924
Chambers 65 mm = 2 1/2"
At the time of proof the barrels weighed 1.369 Kg = or 3.02 #. If > 3% less now (from honing) they would be considered out of proof
The bore of 15.9 mm = .626" is odd; 20g was usually 15.6 mm = .615". The 9 may have actually been stamped upside down.
Muzzle dimensions were not marked after 1924