On the receiver face or water table it should say grade or class with a letter. That looks like a B grade I think.. May have been made by Webley & Scott and finished by Rigby. I have some data but will have to dig it out. Excellent quality, light, well balanced and a joy in the field.
Here is mine. Great sidelock field gun but is in 2.5" Have the factory record somewhere. Sold for £47/5 in 1912 to a land owner in Australia.
Another picture of it in action
