Looks way to new to be original. That doesn't appear to be blued though. Might be the picture, but it looks like regular phosphating. Never seen one that was blued. All of 'em on my MIU long ago were black phosphated. Same thing as manganese based Parkerizing. Parkerizing is a brand name. Manganese based Parkerizing is black. Zinc based is shades of grey depending on the metal it went on.
Mind you, the S/N is very early.
http://www.milsurps.com/showthread.php?t=53153