I would say that if the gun can be accurately dated to 1900, it predates the adoption of the 470NE as a replacement for the various 450s when the ban on 450s came about in 1906-07.
Supposedly the 470 was designed in 1900 but was not commercially available until 1907.
Obviously, it could have been rebored or rebarreled to 470.
Looking at your pictures, the one of the barrel flats is blurry but you can see that there are two weights of cordite charge stamped on them. My guess is a rebore to 470.