Saw an "N" frame with target stocks (mod. 57) that had the serial # removed from grip frame. Upon removing the stocks I found the bottom of grip frame smooth-no serial number. Closer examination revealed a blued steel insert had been dovetailed into frame, with a like section (containing ser. number) having been removed. The ser. number is still present at yoke/crane. I've seen a LOT of old S&W's, but never encountered this. Does anyone have a clue what this is/means? Oh, the revolver is easily 95% with evidence of little (if ever) firing. My thanks.