There were two gunmakers from Birmingham, John Lewis Patstone, who was a gunmaker at 8 Loveday St between 1865 and 1869 and a John Patstone and his heirs and successors operating from 1870 through to 1980. Name variations include John Patstone, John Patstone and Son, Patstone and Sons and Patstone and Cox.
I would guess you have an earlier gun. Please post photos of the proofs and all markings if you can.