Real good link as one guy has a barrel with same numbers as mine. Another guy said that number is a SA drawing number so it is a SA barrel.
Also one guy said Marlin barrels had 'Marlin" spelled out. This barrel as been re-parked as on the outside it looks new, so date may have been sand blasted off and or covered with re-parking.
I alos read somewhere that a "M" indicated a production part as opposed to an experimental part.
Great help, Thanks much!!! Mtnsmith
I do need to email CMP and ask about mixed mfg dates they noted. Odd that one was 6/43 and that was same as guy in link with same barrel number.