Interesting gun Dale. The barrels look to have been sleeved, and should be so marked.
The faint damascus or laminated steel pattern can be seen at the breech.
The original proof marks may have been removed at the time of the sleeving, and new marks placed.
We need a full size in focus close up of the barrel flats and just forward of the flats (I couldn't enhance your image enough to read the marks) - there should be a London date code for the reproof (LP over the year).

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