The 10-6 made for NYSP in .357 Magnum would have a 4" heavy barrel, a counterbored cylinder 1.67" long and a sandblast blue finish. A .400 combat trigger and a checked hammer, notched front sight. Is this what you have?
James: That is odd: a Model 10 in .357. I believe you can write to the S&W historian for the factory configuration of the gun and when as well as where it was originally shipped. The fee used to be $50 (and still might be). You might wish to call S&W customer service for details.
By the way that serial number dates back to 1974-75.
My 10-6 357 (precursor to and the same gun as the Model 13-2) is SN D706428. So yours sounds like it would probably be correct. You don't see them very often.
Ashlander- The 10-6 was made in response to a police order for a heavy barrel M&P (Model 10) in 357 Magnum. Production was limited, and S&W thought it was a good idea so the Model 13 was born. The 10-6 is identical to the 13 except for model number. They are collectible because they were made in low numbers.
They're rare but not completely uncommon. Mostly just not discussed or heard of much. I discovered them through a similar discussion on this forum awhile back, then someone said there was one for sale on some auction site, I bought it immediately. It's deadly accurate, and a super fine shooter in every respect.
They are collectible, obviously, and today you might have to pay more than I did - your nickel plated M10 .357 Magnum, if it's factory nickel, which I will presume without inquiry, is at least a 500 dollar gun today, I GUESS. Emphasis on guess.....
So I called s&w and the lady on the phone, who was very polite and helpful by the way, informed me that my 10-6 .357 was in fact produced in their factory and not a Frankenstein now I just need to get the paperwork and box for it.thanks y'all you've been very helpful in this matter