I agree that looks like a stock 15-3 with a strange serial number. One thing I notice is that the two corners of the grip frame look a little sharper than I would expect. Even square butt guns have slightly rounded frame corners. It's almost as though the butt of this one was planed to remove the original serial number and then restamped with an old C-prefix number. (Not that I seriously believe that actually happened. I'm reporting a notion that crossed my mind.)

Whatever their model number designation or serial number, two-inch CMs are very cool guns, and I give that one an appreciative upturned thumb.

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David Wilson