It is a forging for the M1 bayonet*. Many machining operations would have been needed to complete it. It could have come from any of the factories making the M1 bayonet just before or during WWII, but not from Winchester, which never made the M1.
* The M1 bayonet and M1 rifle are not directly connected except in the coincidence of the nomenclature. The Bayonet Knife, M1, was issued from the late 1930's into the 1960's. It fitted, and was issued with, the M1, the M1903, the M1903A3 and M1903A4 rifles. It was superseded for the M1 rifle by the M5 bayonet.
FWIW, the "blood groove" is a basic training myth; it is properly called a "fuller" and is intended to lighten and stiffen the blade, not to allow the victim's blood to come out.
Last edited by James K; March 24, 2013 at 05:22 PM.