Stevenson is a popular name. (The nobility is something of a red herring, I suspect. Even in Victorian times GB was not full of nobility, you know!)
I have found a JOHN Hugh Macdonald Stevenson in the 1911 census, as a Lieutenant in the Royal Garrison Artillery, based at Shoeburyness, Essex. However, he was born in Middlesex.
Can you please confirm the actual information you have on this chap, perhaps what is written on the gun case or from the firm's records (which firm, by the way?) Where does Cornwall feature? Then I may be able to dig a little deeper for you.
Tim
