Nice! I have a similar rifle. Marked 'Watson Bros.' on the rib. Same separate soldered on assembly.
Mine was 303 but a burned out bore. Now a 35.
Birmingham Black Powder Proof & View marks. The View marked after the rifle went through the actual proof, was inspected and passed.
Also looks like a London Proof House 'Final Proof' (BP) mark there too on the bbl closest to the frame.
Guessing it was proofed at London origianly and went to Birmingham for re-proof after some work performed at a later time.,,maybe a conversion to 450 from ??
I think the .450 is bore diameter but I also thought case length was to be marked as well.
What do I know other than I like the rifle!
