It depends on the proof marks. If English, then:
William Moore & Co., London
Gunmakers at 43 Old Bond St. from 1854 to 1872. Became Wm. Moore & Grey in 1873, and a Limited Company from 1879. They moved to 165 Piccadilly in 1896.
Wm. Moore was appointed gunmaker to King William IV in April, 1836.