Yes, it is W.W. Greener. I had fairly extensive correspondence with Graham Greener, current head of the firm, and after providing him with all information on and many photos of the gun, he said: “There is no doubt that your percussion muzzle loader is a genuine W W Greener example in good condition for its age. The serial number of 10792 indicate a manufacturing date between 1871 and 1873 but probably towards the earlier year.”
Spence