Proofmarks on this gun are interesting. The original ones are London and look to be from 1887-1904. (After 1904, the shot charge would have been marked.) It then looks as if the gun got a Birmingham reproof--the crossed swords mark, which did not appear until 1921. I can't make out the letter in the left quadrant of that mark, but that would give you a date of the first reproof. The latest reproof is quite recent, because the STD under a crown--which means that the gun is proofed for only standard ammunition, not high pressure (avoid American factory 2 3/4" loads, as indicated above)--only came into use in 2005.
Hope this helps.
