I think that using anything other than FMJ ammo is a violation of Art. 23e of the Annex to Hague Convention IV Respecting the Laws and Customs of War on Land of 18 October 1907. The USA is not actually bound by this document but has always as a matter of principle adhered to it. It was an attempt by countries to stop the use of soft rapidly expanding bullets that caused huge numbers of limb amputations in prior wars.