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