Could be that the military isn't using WC842 in M855.
Could be that there's enough flexibility in the powder and load that a slower lot of the powder can be charged that much higher and still meet velocity/pressure parameters.
Could be that your loads are dog-slow.
Could be that CFE223 is not WC842.
Could be none of the above.
Just my initial thoughts; I was hoping for closer charge weights between your trials and surplus ammo.
I essentially don't shoot surplus ammo. The charge weight you pulled down is a lot closer to what I would personally expect a 748 charge to be.