Saginaw general motors barrel

[Sunray]

Like jond41403 says, not all barrels were date stamped. Not all of 'em were ground smooth either. Not all the manufacturers made barrels at all.
Way down near the bottom they talk about Ordnance Bomb stamps.
The U.S. Caliber .30 Carbines - Barrel Manufacturers
If you haven't been to that site before, all the links work. Keep you busy for a few days reading it all.
"...not sure if it's WW2 new..." Saginaw S. G. only made Carbines during W.W. II. May 1943-April 1944. They also made a whole lot of other stuff.