The Browning Double Auto model was made from 1952 - 1971. The FN on your gun is not part of the serial number but stands for FN the manufacturer. Your serial number is 54831. There were no records kept by Browning between 1951 and 1959 as to the dates of mfg. The Double Auto had a serial code that started in 1960 with a letter prefix. Your gun was probably made in the mid 1950's.