I was in a bit of a rush when I made my original post, so in addition, this is a 12 gauge Damascus barrel (30 inch), rebounding hammer shotgun, with no discernible markings on the rib, nor, with the exception of the proof marks (Birmingham) on the barrels and frame, anywhere else on the gun.
It is certain that this is in its original, as-built form, has been used very little (locks up tight, the locks operate crisply, and there is virtually no wear to the wood or metal).
It has what I would consider unusually fine wood, engraving and checkering for the period (we have an nice 1894 Westley Richards that is more plain).
I know that several of the well-known manufacturers made guns that retailers (particularly purveyors of fine goods in Bombay, Calcutta and N. America) could sell under their own name and engrave accordingly. Perhaps this is one that just never got marked (Marqued?).
Stallone, if you take a closer look, you will see that this gun has a squarer mid-frame section, larger hammers and entirely different side locks than your W. A. Moore.
Any more guesses, anyone?