What AkMike1 says is right on the money! I am a collector, not a shooter and really like to find out who the rifle was made for and as much about it as I can. Your rifle was made pre 1875 from the serial number. I have some Alex Henry copies of ledger pages and will see if your rifle is on one of them. I used to own a .577 Alex Henry Dr and a 20 Bore Alex Henry DR consecutivly numbered and made approx 1875 for the Maharaja of Pattiallah (inscribed on the rib of both rifles. Sold them too, the 20 Bore is pictured in Dr Findlow's article. I would have to say that Alex Henry was at LEAST equal to any of the best London makers.
Dicksons Gunmakers have the Henry records in Scotland. Because of some stupid law suit they will probably not tell you the owners name, but will give you the rest of the info on the rifle. For example my 12 Bore Henry Double Rifle was made in 1879, weighs 12 lb 13 oz, regulated with 6 3/4 drams of no. 6 powder with a conical steel cored bullet.
