Welcome aboard OSA. We have a milsurp section so hopefully one of the mods can move this post to that section. M1 carbines are a blast and it sounds like you have a genuine USGI unit made by IBM during the war. The RRA mark is for the Red River Arsenal. Is there an import mark on the bottom of the barrel near the muzzle? If so it might be something like "Blue Sky". Is the serial number of the receiver also engraved into the stock?