It is possible that earlier guns were sent in to be reproved for use with nitro powder leading one to believe that it was done earlier.
This gun was obviously made before 1896.
William Richards, Liverpool and Preston
The firm was founded in 1801 by Wm. Richards in London. Wm. Richards died in 1820 and was succeeded by his son William who came to Liverpool via Birmingham in 1842 and died in 1864. His son Henry carried on the business at various addresses in Old Hall Street, and finally at No. 27. Henry died in 1895.