Re: Approximate value?
The adjustable sights nail it down to only two models...the M12 or M15...the first produced from 1970 to 1971, and the latter produced from 1971 to 1975.
The first interchangeable barrel pistol produced was the W12, or the Dan Wesson Model 12 which was chambered in .357 Magnum. The barrels and shrouds for this model were interchangeable and used an exposed nut on the muzzle end to secure the barrel and shroud. The shrouds on these early models had an elongated flange which helped to center the barrel and properly secure it.
Later, this design was refined into the Model 15 which still used the flanged barrel assemblies, but which had the nut recessed inside the flange in order to give the pistol a more conventionally finished look. Further refinements to the model 15 resulted in the Model 15-2 which is the most well known as well as the best selling Dan Wesson model. The 15-2 used a roll pin inserted into the frame as a centering dowel combined with a precisely drilled hole in the shroud assembly to facilitate proper shroud centering and alignment, thus eliminating the flanged barrel shrouds.
The 15-2 also introduced more barrel offerings, including lengths of 2.5, 4, 6, 8, 10, 12, and 15 inches, venting, ribbed shrouds, shrouds with full underlugs, and plain solid shrouds. The pistols could be ordered as "Pistol Pacs" with 3 (initially) and later 4 (or more) barrels shipped inside a fiberglass briefcase with barrel changing tool and clearance gauges; however, many pistols were sold with only one barrel, though owners could choose to purchase other barrels later.