That serial number places shipment of yours around mid-1950. The C-series M&Ps were the first manufactured with the new short action design, which S&W called the "High-speed Hammer," beginning in mid-1948 at about SN S990000, just prior to the beginning of the C-series. The C-series was in production from 1948 until 1967, with one million made. This revolver became the Model 10 in 1957, when S&W adopted a model numbering nomenclature (at about SN C430000). Yours would be correctly called a "pre-Model 10" by collectors, and never had a yoke Model 10 stamping, only an assembly number. There is nothing rare or unusual about the C-series in .38 Special. Those having a 2" barrel are more desirable than longer barrel lengths and will bring higher prices. An average-condition C-series M&P will have a private sale value in the $300-$400 range. One in exceptional all-original condition may be closer to $500, especially if accompanied by the original box.