"London Gunmakers" By Nigel Brown, Christie's Books, 1998, list George & John Deane, wholesale ironmongers, 41 Fish St.Hill and Corner of Arthur St. Monument 1830-37, with succession of other, addresses and dates up to the company name, Deane, Adams & Deane 30 King St. and 1 New Weston St. 1853-1855; 30 King St. 2 New Weston St.1856-57. So you can date your gun to have been made between 1853-1857.
David Baker's "The Royal Gunroom at Sandringham" Phaidon-Christi's Ltd. 1989, have the picture of a "splended" gun, made for Prince Albert 30 King William St.London Bridge, by George and John Deane, of 30 King St. Deane, Adams & Deane exhibited at the Great Exhibition. Baker goes on to say that "At this time their gun department was managed by a man destined for fame in the story of British gunmaking, Robert Adams. He was to design the revolving pistol that bears his name." The gun discussed in Bakers discourse is beyond description.
It appears you have a marvelous piece of weaponry with a marvelous pedigree! I hope this has been of help to you.
