I just posted this same reply on the S&W Forum as well.
Here are a couple of pics of my 1957 Pre-Model-14, 4" Target Masterpiece (s/n K292XXX). This is a factory barrel as can be seen by the centered position of the lettering, crown, etc. For comparison I also show my Pre-15 1952 Combat Masterpiece with the common tapered barrel. It is true that S&W never cataloged a 4" bbl for the Target Masterpiece/Model 14 (only 6" and 8 3/8") but some 4" guns were produced on special order.
This may be one of the Kansas City, Kansas Police Dept. guns referred to on page 144 of Supica and Nahas - Standard Catalog of S&W under Variations. The year of manufacture is correct and the fact that it came from a gun shop in Independence, Missouri lends credence; however I have not had it researched as yet. Anyway, I wanted to show the difference between the the 4" Model-14 (and pre-14) guns and a standard Model-15.
The "Dayton" guns have what appears to be a Model 10 heavy barrel with Baughman ramp front sight added to match the height of the adjustable rear sight. It is a significantly thicker barrel than either of these pictured.
Chris