It is post 1925 and they more or less stopped production around the Second World War. It has a high serial number so I would put production date around the mid 30's The model you have is The 'Favourite' Hammerless Non-Ejector. Records were destroyed in the war. I cannot quite read the date code which is the small letter in the crossed sceptre mark on the barrel flats. If you can make that out I can date exactly. Lagopus.....