Thanks for your comments.
I'm pretty sure it's 1901. The serial number of 13956 dates it within a few months based on my research, though I'd love to be able to buy the original record. The business of only black powder proofs is explained by the extra cost they paid for nitro. Nitro proofs only became general in 1904. There's some period literature on the net that shows that even in the late 1890's, only a tiny fraction of guns were submitted for Nitro Proof, though it was in general use. It was the extra shilling charged for nitro proof at fault, or something like that.
Boswell had some quarrel with the London Proof house and sent his guns to Birmingham for proof I read somewhere. The gun reads as improved cylinder on the right barrel and improved modified on the left barrel. Yes the woodwork is quite worn and it has a repair to the hand. It would have been a lovely piece of walnut when new though.
https://d6d2h4gfvy8t8.cloudfront.net/18592608-orig.jpg 
