M&P in general are not that valuable. They were S&W bread and butter guns. They were the Toyota Corolla of their day. Solid, reliable, inexpensive and mas produced. Most people could afford a M&P. In 1957 the name changed to model 10 and they are still made today. Typically they are 38 special caliber so the 38 Long Colt could be worth more or less. I see them around $350 +/- depending on the condition and accessories like the original box.

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