Are sure it is not Bartram?
G Thorpe Bartram was recorded as a gunmaker in Braintree, Essex in about 1900. In about 1900 he claimed that his business had been established over a century but, obviously, he bought or inherited the business.
He was a gun dog breeder who won over 100 cups and First Prizes. He won a First Award at Crystal Palace but what for is not known. His gun case labels claimed he made a speciality of gun fitting, and was patronised by Royalty; "His Highness says the gun is very good and cheap" (Prince of Wales).
The firm sold cartridges under the name "Yellow Seal".
Pete