Louis and Deeangeo, thanks for that; its very helpful.

It's really interesting isn't it - my rifle is very similarly marked to yours Deeangeo but it doesn't have the NVP mark. So as Louis noted, probably assembled and proofed in the UK (London), and maybe sometime between 1904 and 1925??

Maybe it would help if I did some additional research on British and particularly London proofs. Maybe the words "Nitro Proved" can be dated or perhaps the circled "T" on my rifle.

There are one or two other marks that may also be traceable.