Without any information on the rifle itself, or any pictures of the gun and its various markings, it is not possible to help you very much.
As to the maker, the following is taken from the Internet Gun Club Database. William Sumners (born 1826 in Liverpool) is known to have worked for Williams & Powell, he may have been apprenticed to them. He was recorded in the 1841 census as a 15 year old apprentice gun maker living with his parents and his twin sister. William left Williams & Powell in 1858 to establish his own business at 219 Oliver Street, Birkenhead. He was recorded in the 1861 census living at 219 Oliver Street with his wife, Mary J and three daughters, Helen, Mary and Kate. He was recorded at this address up to 1860. In about 1875 he was recorded at 48 Oldhall Street. In the 1881 census he was recorded at this address. Another son and daughter had been born, John and Blanch, but between 1866 and 1881 his first wife, Mary J had died and he had married again, his second wife also named Jane. In this census he described himself as a master gunmaker. In about 1883 the firm's address became 48 & 50 Old Hall Street and at about this time he made his son a partner in the business which was re-named William Sumners & Son. The firm appears to have closed in about 1890.
By the address on your gun it might be possible to narrow the build date. No records for this gunmaker have survived, so the serial number is of no help.
