According to the Standard Catalog of Smith & Wesson your 645 was made in 1987. The 645 was produced from late 1985 through 1988. It was discontinued with the introduction of the 3rd generation. There was overlap production of the 645 and the 4506 that it basically became. These transitional guns had features of both.
My 645 is an incredible gun. I had a 4506 acquired in 1988 and prefer the 645 which I shoot as often as I can. You couldn't ask for a more reliable gun. It is true that it will even reliably feed empty brass (as will the 4506, I'm told).
If your gun has the Philips or hex head bolt securing the right safety lever I would strongly recommend applying some blue Loc Tite as it will most likely loosen otherwise.
While I highly value my 3rd Gen Smiths my 2nd Gens (645, 669, 659) are my favorites.
Last edited by Que; January 14, 2013 at 10:02 AM.