Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Condition and age is also a factor. Auto 5's with recoil pads (other than Mag 12's) poly-chokes and compensators will reduce value. Recommend taking it to a gun shop for appraisal.
You can also do your own investigation by looking at other models being sold that are in the same condition as yours. Try the gunbroker.com or a periodical called "The Gun List"
You can also reference the Blue Book of Gun Values which can be purchased on line at various retailers.
400 or so
A Browning A-500g shotgun in excellent condition is worth about 900 dollars.
100-400 usd
What is an A-5 light 20 Belgium Browning made in 1961 worth
500 USD
About $550 for plain barrel, $850 for vent rib. This is for EXCELLENT condition, lesser condition less $$$.
Your browning auto-5 shotgun was made by FN of belguim for browning in 1938.In the condition that you describe your shotgun should be worth between 450-550 dollars.
50- 500 usd
what is a 1988 Chevy Beretta 5 speed V-6 with 74,000 miles on in excellent shape worth
Excellent shape $1200. Poor shape $250.
50- 700 usd
Browning.com has sn data under customer service.