Operating from memory here, but if I recall correctly the fact it has the 12/C chamber marking makes it a post 1887 date. Interesting it has 12ga chambers but only 14 bores. The intermediate bore markings began the same time as the chamber mark so these bores would have been no larger than a 14/1. 14ga = .693" with 14/1 @ .702". 12ga = .729". I have an old Birmingham proofed W Richards which also has 14 bores with a 12ga chamber, but it predates 1887 ( no chamber mark on it) . This gun could conceivably have had bores very near to 13ga (.710") when new. They measure very near that now but are badly pitted so cannot say how close they are to original.
