To; Vol423,
I would suggest that your Gibbs-Farquharson, APUN 586 / Metford's BPUN 1763, is not the same rifle illustrated in Winfer's Vol. 2, p. 66, Fig. 69, APUN 536, which has a barrel "in the white", as is described in the caption and shown in the photo.
Where as your rifle has a blued barrel, and from the crispness of its markings, it is unlikely to have been re-blued. Jonathan Kirton
It is absolutely the same rifle.
Look at the little rust stain just in front of the cocking lever as well as the angled dent in the forend.
BTW, I admit to being the caller mentioned above...