I have been searching for this one since last night, without success. Dating the gun at 1872 (or later), by the "& Sons" description and Brown's chronology putting it around 1874 the only patent that comes up is Woodward & Emme # 267 of 1872. From what I can see of it, does not tie in to this gun but maybe a variation for whatever reason ?.
Woodward was apparently at that time trying to find ways round the Purdey bolt system.