What is the value of a Winchester Model 12 12 gauge trap shotgun serial 257895?

The Winchester model 1912 trap shotgun was made from 1938-1964.With the serial number that you provided,your model 12 trap shotgun was made in the year 1921.It could be that yours may not be a trap model due to the date of manufacture!That being said a model 12 trap shotgun will bring between 700-1,200 dollars depending on the overall condition and a good bore.