I have an Alexander Henry Hammerless double rifle in .450 express that is identical to yours. The patent number on it is 245 and the serial number is in the 6700 range. The records show that mine was built in August of 1893 for His Grace, The Duke of Portland. Yours, according to the patent number, would have been built earlier than 1893. I would suggest that you call Dickson & McNaughton and pay a small fee to have the information on your rifle E-mailed to you. They are very nice to deal with. I think that the rifle that you have was featured in an issue of Double Gun Journal a few years ago and is quite a unique collectable rifle. I have owned a number of British double rifles over the years and in my own opinion Alexander Henry rifles are equal in quality to the very best makers. They are built like a fine watch.