Go to Browning's website under Support then go to Date your firearm. Value of any used firearm depends upon condition and area of sale.
Magnum
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.
Your serial number indicates that you have a Browning auto-5 magnum shotgun that was produced in the year 1965.
Your serial number indicates that you have a Browning auto-5 Magnum shotgun that was made in the year 1965.
You Have a Browning auto-5 shotgun that is a Magnum chambering which was made in the year 1968.
1962 auto 5 magnum
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.
Your browning auto-5 magnum shotgun was made by FN of belguim for browning in 1965.
The 4V prefix to your serial number indicates that you have a Browning auto-5 Magnum shotgun made by FN of belguim,in the year 1964.
You will need to provide the number and letter that proceeds the serial number to your shotgun to have the date of manufacture answered.
Your Browning auto-5 shotgun with the serial number 73v18957 indicates that you have the magnum version of the auto-5 and that it was made in the year 1973.
You will have to call Browning with the serial number.