AZCarbineFan

I am a machinist by trade and I can tell you that the type of tooling marks you are saying are from a fly cutter can be by many types of cutters. I would guess that they were more likely made on a horizontal mill with a custom tool on multiple receivers in a part specific jig or vice. These are still used in many production shops with auto feed and return to cut grooves or slots in mass quantity parts and you will not get tooling deflection as you would from a vertical mill.

As for the two carbines They have both been rebuilt at some time and would not have a tremendous premium over CMPicon prices unless you had to have one or the other for some reason.

I would like to see your S'G'. An inland barrel would not be to unusul as the grand rapids plant used barrels from the government free issue program so it could be correct. I would figure the barrel date would also be in the later months of 1943 based on your rifles SN.