YOu must provide the serial number.
It shouldn't say light twelve on the barrel, but on the receiver. Light twelve means that the gun is a light weight version of the standard Auto5 shotgun.
Go to Browning.com and you can download a manual
By this serial number for an Auto5, the gun should be a Light Twelve 12 guage model made in 1956. It is not a Sweet 16.
Your serial number indicates that your Browning light twelve was made in the year 1955.
This is a mixed question. Which gun do you have? An Auto-5 Light twelve, is not a pump shotgun, it is a semi-automatic. Since 1979 is before the Browning Pump Model BPS was introduced, It is assumed you do have an A5. Value depends on condition. Typically with average use, these guns sell in the range of $500-$750 depending on condition. Mint in the box will go $1000+, but remember that this model has a fixed choke in 1979 and won't bring as much as the later Janaese made Auto-5's. The nickel plating you mention is not Browning factory finished. Browning never plated an auto5. You could have a silver receiver that was custom engraved, but it wouldn't be plated. If someone actually did nickel plate the gun, it could decrease value.
The serial number L52789 indicates that you have a Browning light weight model,auto-5 shotgun which was made in the year 1955.
Good shotgun
your browning auto-5 light twelve gauge was made in 1960.
Readily available from Browning.
your browning light weight 12ga was produced in 1960.
If your browning auto-5 is in excellent condition(85-90%)original finish?I would assign a value of 550-650 dollars.
The Browning light weight 12 gauge shotgun was made by FN for browning from 1947-1976.These shotguns were also made by Miroku of Japan from 1976-1998.If you would supply a serial number to your browning shotgun then I would be able to identify the exact year of production.