Can't be answered without a detailed description of all markings, barrel length, finish, condition, box, papers, accessories.
If you mean serial number 27,078,977;then it was made in 1973.
Your serial number indicates that it was made in the year 1973.
The winchester model 670,and magnum models were made from 1967-1973.
This gun is a 12ga Magnum made in 1963.
About 1968/1969.
Your Browning auto-5 magnum shotgun was made in Herstal,Belgium by the firm FN(Fabrique Nationale)for Browning in the year 1965 with the serial number that you have provided.
It is a Magnum made in 1966.
See related link.
The letters PY that are in the middle of your serial number,indicate that your Browning Auto-5 Magnum shotgun was made in the year 1982.
This gun is a 12ga Magnum made in 1963.
It will be marked where it was made.
This was made in 1969.