The S&W Model 66 was introduced in 1973. It is the stainless steel version of the Model 19 Combat Magnum. It is a 6 shot double or single action revolver with adjustable sights, a square butt with checkered walnut grips. It was first available with a 4" barrel. In 1974 a 2 1/2" round butt version was introduced. It was also made with a 6" barrel. It was discontinued in 1993. The values from the 2012 Standard Catalog of Firearms are:
New in Box-$575, excellent-$400, very good-$250, good-$200, fair-$150, poor-$125.
For a gun with only 50 rounds through it, I would put the value at $500 to $525.
I hope this helps you,