A project of this size of the Iwo Jima Memoial would have had technical advisers to the artist, Felix de Weldon, those advisers slipped up on this one. Mr. de Weldon paid close attention to detail including having the three survivors model for the sculpture. If you notice, the men carrying Carbines have the correct cartridge belts. Also notice Pfc Ira Hayes has his poncho tucked into the back of his cartridge belt.
In the greater scheme of things the Carbines are no big deal, just interesting from a collectors point of view. Thank God no one gave the artist a BAR or a Thompson.