Hiwall is correct- that is a pinfire shotgun. The action may be a Jones underlever- used by a number of gunmakers in Britain. Your gun COULD have been made in another country, exported to Britain, which required all imported guns to be proof tested.
To the OP, you were not given a range of dates of manufacture- those were the dates during which the government proof house used those markings.
Lighter, larger pictures showing makings on rib, on the side plates, etc would help a lot.
If you are not familiar with pinfires, it is an obsolete priming system, neither rimfire nor centerfire. Each shell has it's own firing pin, gun has none. Predated centerfire priming, which replaced it. Modern shotshells will not fire or fit. They look like this:
More photos of her
Linear Mode
