During the 1960s the US military was running low on original M1917 bayonets for the M12 trench-guns.
So they contracted General Cutlery in Ohio and the Canadian Arsenal ( the old Long Branch arsenal ) to make a run of M-1917 bayonets. You do not see many of the Canadian made versions. This would be period correct for a later model military shotgun with a bayonet mount. It has some arms room paint on the opposite side of the grip that could probably be removed with some solvent and a toothbrush.