During the end of production at S'G' they sent what ever was left to S.G. and that included barrels from the free issue program but that was in January 1944. Now when S'G' took over the IP plant they used IP marked and serial numbered receivers before they even started to make their own receivers. When they did they started using the IP serial numbers that were not used because of it having been used on a bad receiver. They started to appear in the June 1943 time frame and when S'G' had used all of the IP numbers they then picked up in the serial number blocks where IP had left off. A key bit of information will be the barrel date on the Underwood barrel. If the barrel is original to the receiver it will be an S'G' receiver. S'G' only sent receivers to S.G. not barreled ones. S.G. made their own barrels.