Without more specific information; 100-1000 USD or so
A staple of the Browning line since the 1930s
If your over under shotgun was made prior to 1964,then the model of your Browning shotgun should be named the superposed.
Best left to a gunsmith.
Your Browning superposed,over under 20 gauge shotgun was made in the year 1951;with the serial number that you have provided.
You will have to contact Browning and order a history letter.
40891 s5
100-1000 or more depending on specifics
A few hundred to a few thousand.
In order for me to answer your question,I will need some more information from you.First is this shotgun a semi-auto,pump action,or over-under shotgun.I will need the model of shotgun.Then add the shotguns gauge(12 gauge,16 gauge,20 gauge)? I will need the serial number of your shotgun to date the year of manufacture.If you provide this info,I can then tell you how old your Browning shotgun is.
Browning.com has sn data under customer service.
800-1100 USD or so
Are we talking about a auto-5 shotgun,or a BPS(browning pump shotgun),or a over-under shotgun(citori, or superposed)These answers would help me determine the value of your shotgun which was made in 1980.