I have just obtained my Dad's service revolver and am interested in dating the revolver. Listed below is the info I currently have

Military - 38 - Police
Blued 4 Inch
Square Butt
SN 172xx

Any help is greatly appreciated!

That is the serial number off the butt, not the fitting number inside the yoke?
No letter prefix like V, S, C, or D?

If yes and no, that is a very old gun, maybe 1901.

Welcome to the forum. Treasure that one.

I don't think a square butt would be possible with that low a serial, which is pre-Model 1905, so I do indeed think that is not it.

The easily viewable SNs would be on the butt, on the bottom of the barrel, and the rear face of the cylinder. Whether or not there is a letter prefix is very important to identification. With a square butt, it would necessarily be from 1905 or later, and the SN would be much higher than you provided. Therefore there must be a letter prefix. What kind of service - Police? Military?

Gentelmen,
Thank you for your responses. The number I provided is the serial number. My Dad was a retired NYC police officer. The numbers on the stock, cylinder and barrel are 846953. Additionally, on the stock is S 3126. In addition, I have the original revolver box where I provided the info on the original post. Your info is truly valued. Many thanks.

846953 would suggest your M&P was shipped from S&W around November 1941. At that time, relatively few civilian revolvers were being sold to anyone, as most of S&W's handgun output was going to the British Military. You are very fortunate if you have the original box as it adds considerable value. Please post some pictures, and we can see if the box is original. I can't say what the S 3126 on the stock means. Is there any other number stamped on the inside of the right grip panel?

The numbering scheme you describe does not compute.
Please show close clear pictures of the gun, its markings, and the box label.

Makes perfect sense now. The S 3126 would mean "sergeant" plus his shield number if he was indeed a NYCPD officer. What you refer to as the stock I assume to be what we call the grip frame; the S number was commonly applied either on the backstrap or squeezed in next to the serial number on the butt (the bottom of the grip). The number you identlfy as the serial you likely obtained from the frame cut-out when you open the cylinder; S&W revolvers of that era do not have a serial number there, just (for us) irrelevant assembly numbers. If that number came from the box, I'm officially puzzled. But the fact that the 846953 matches in three main locations leaves no doubt that this is indeed the one and only serial number.

Is there anything on the bottom of the grip frame?
That is where the official legal serial number is supposed to be.
Numbers on other parts only serve to show whether they are original to the gun.