Impossible to answer without a detailed description and the serial number.
I purchased it in 1965 but have no idea when it was made
Browning records of serial numbers on the 1910/1955 model are vague before 1966. They estmate that number 500,000 was made around 1965, and that 550,000 was the beginning of serial numbers made in 1966. Yours is probably 1965.
In the 100-1000 USD or more range depending on specifics.
You simply drop the magazine, then you pull back on the slide to extract the round.
A Pistol for Ringo was created on 1965-05-12.
Frederick Browning died on 1965-03-14.
Your browning auto-5 magnum shotgun was made by FN of belguim for browning in 1965.
Your browning model auto-5 magnum 12ga shotgun was made by FN for browning in 1965.