Up to about 50 years ago S&W would place the serial number on all the major parts of the gun (grip butt, cylinder, barrel, etc.). Then they went to the grip butt only for the SN and started using assembly numbers on the major parts. Not too long ago they would sometimes also put the serial number on the frame cut-out, but since the frame cut-out and the grip butt are on the same frame they would have to match. Otherwise, they're assembly numbers.
The one constant (with the exception of the Regulation Police models) has been the bottom of the grip butt so that's the "official" location.
Last edited by laytonj1; January 18, 2011 at 06:55 PM.