Nice old revolver. Others may be able to give a better date, but the Standard Catalog of S&W doesn't come any closer than your estimate. Postwar S serial range is 1945-1948: S811120 to S999999. I'm sure you know those are not the original grips. Very good condition for a gun that's almost as old as I am. Can't tell from the pictures if it's been refinished. If so, it was a good job and retained the original markings.
I wouldn't store it with those Pachmayr grips on it. They are notorious for pitting the metal over time, even stainless. If they feel right, put them on when you take it out to shoot & remove them before storeing. Shooting it all you want is fine, it dosen't harm the blue finish. Holsters, rubs and rough treatment do.
I don't see any reason not to shoot this gun as often as you like. Just because it is about to reach middle age is no reason not to enjoy life. You won't hurt it or it's value.
Shoot it much less ? Good Heavens, my friend, that is the function that particular piece of machinery was designed and built for ! You're not going to do it any harm, and you'll enjoy one of the finest quality revolvers the world has ever known.
Shoot, clean, oil, repeat as desired !
Hi
S923665 probably shipped in August or September, 1947.
That is a nice 4" example and I'm fairly certain it has not been refinished. I second all the comments regarding the Pachmayr stocks. Nice for shooting, but they do not look quite right on that M&P and the gun should not be stored regularly with them on it.