Hi Ben,
Here is what I see from the marks-
The gun was nitro proved in London for 1 1/8 oz. loads and the chambers are obviously 2.5" long.
Barrels are dovetail lump and were re-proved at some time. At the time of re-proof, the bores (9" from the breech) measured .736" in diameter and this can give you an indication of how much that they have been lapped.
There are no choke markings on the barrel flats so either the gun has no choke or the marks were struck off at some time. You must measure the chokes as described above to determine what the choke is. Choke tools that do not tell you the difference between the bore and choke are useless.
You must measure the bore diameter and determine if the gun is still in proof. If the bores measure more than .746", then the gun is out of proof. You must also measure the minimum wall thickness to determine how safe the bores are. You will get many different opinions about wall thickness here so I may as well give you mine. If the walls are over .020" thick at their thinnest point and the bores are still in proof, you are good to go with either low pressure loads or CIP approved ammunition.
