They are forged. I bought one late last year from another vendor that was an early one (1996) with forged, flash chromed internals. The 640-1's were introduced in 1995 and were the first of the ".357 magnum" J-frames. What is your ser# prefix?

The Centerfire examples I've seen range from really good condition to awful. (mine was awful) The one I bought from Centerfire has MIM internals that had received a regular bath of WD-40. Fortunately, the liquid hadn't turned solid as yet and a little soaking removed most all the crud.

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Ret. LE, FA Instr, S&W Armorer