My 642 is one of the early ones. No lock and no SN on the butt. It's on the sideplate. I've changed over to Hogue Boot Monogrips for most of my j-frames. It's one-piece and gives a nice feel and isn't much larger than the original Uncle Mike's two-piece grips. Airweight and lighter j-frames are considered "expert guns", meaning you have to put a lot of range time in to really master them, but it's worth the effort. I carry Corbon DPX in mine. Good luck with it.

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