I currently own a Field London gun - likely mid 1880's.
Nice damascus bls. with some minor engraving and most of the colour case hardening still there, likely 90% or 95% & with hammers, no chokes. Bores are in very nice shape.
I used it for the black powder trap shoot at rendezvous last fall in the ctg. event - placed second - 1 bird lost, dang. It seems to like 75gr. 1F and 1 1/4oz. 7 1/2's in both barrels.
Of course not even in the same ball park with the Rigby or most other English guns.