Based on barrel address (29 Old Bond Street London) the rifle was made between 1895 and 1929/1930. A 500NE Watson double, #13595, sold at Morphy sold last year -- that rifle was described as circa 1907. Mine is #13566. Strangely, I also found #13557 from a 2001 auction at Butterfield & Dunning that had a 7 Bury Street address, which should be after 29 Old Bond. Not sure if that's a re-barrel but that would be an earlier serial number at a much later address (post 1935.)

If the screw grip patent expired in 1902 and my rifle is still marked 'patent', then I would expect it is between 1895 and 1902. Which would be consistent the rifle's light weight and probable NfB loading (based on the vintage ammo stashed away by it's previous meticulous owner.)

Would welcome any help on dates pending a reply from Watson's.