The Model 12 was Winchester's first hammerless slide action shotgun. There were over 1,900,000 produced. The 16 gauge was made in Standard, Skeet and the special order Pigeon grades. Value will depend on the grade and options.
For the Standard grade, values are: exc-$800, very good-$500, good-$400, fair-$300 and poor-$200. It can have a 26,28,30 or 32" barrel and it can be plain, have a vent or solid rib. The stock is a plain pistol grip walnut.
Skeet grades are double in value with checkered stocks and forends.
Add 20% for solid ribs, 30% for Winchester Special ventilated rib and 40% for milled ribs.Add 20% for 32" barrels. Deduct 10% for 16 gauge.
If you give me the serial number, I can give you the year of manufacture.
It was made in 1958. Assuming your gun is in very good condition, I would value it between $540 and $600. There has been a big demand for older shotguns and model 12's are very collectable.It could go much higher. There is a 16 gauge with a solid rib on Rock Island Auctions that they expect to bring between $1100 and $1400. If there is anything else you need to know, let me know.
After looking in a different book, it lists higher retail for your gun. In very good condition, it is worth around $860 to $875.
from what i found out about the serial number, it wat made in 1918.
1918 serial numbers ended at number 183461. I have verified it at two different places. here is a link to a website for Winchester dates of manufacture.