The Berry Amendment is a WWII law that requires that the DoD give preference to American suppliers when procuring items. It has been amended many times, such that some items (including some types of steel) are required to be supplied by American companies. However, it was again amended in 2004 stating that it can be waived in times of compelling need.
Since our troops are currently using ammo faster than American sources can make it, this waiver applies. Also, I do not believe that the tiny steel core in M855 ammo would fall under the jurisdiction of the Berry Amendment, but I could be wrong. Regardless, even if it does the compelling need waiver is in effect.
I would think the waiver would come from the DoD. This contract was initiated from a U.S. military subcontractor and not directly from the DOD.