Antique Victorian intaglio spinner fob pendant 15 carat gold

Era: Victorian 1837-1901
Metal: 15 carat gold tested
Gemstones: Bloodstone and Sardonyx 15.8mm diameter each
Size: 26.5x22.6mm
Weight: 6.4g
 
A fascinating piece of history, I knew this was a special fob when I first saw it, because of the extraordinary care and detail that has gone into engraving the gold borders and its high carat construction. 
 
However upon digging a little deeper I suspect this seal could have strong links to British nobility. The sardonyx side of the fob features an intaglio carving of a heraldic crest belonging to the Seymour family, or the Dukes of Somerset. Out of a ducal coronet, is a phoenix rising from flames, with the wording 'foy pour devoir' or faithful to duty, written in a garter belt around the edge.
 
Under the imagery of the phoenix are three faint initials, frustratingly faint, as this would be the most helpful part to identifying who the original owner of this wonderful fob was. I can make out for certainty that the last two letters read B.S and having read into it, there are several possibilities, the most likely and notable of which would be A.P.B.S, Algernon Percy Banks St Maur, the 14th duke of somerset. He lived from 1813 to 1894, becoming duke at the age of 77, which would fit well with the period of this style of fob. Whilst this is all very exciting, I cannot prove the connection, so it is just my own speculation about this piece.
 
It is in very good antique condition, with some minor wear to the gold frame and surface wear to the sardonyx side of the fob, consistent with use. The chain in the photos is not for sale.