See: US Army Considers Adopting an Interim Battle Rifle in 7.62 NATO - Soldier Systems Daily Haven't we done this before?
This argument has been going on for 75 years. Ian Hogg, the noted British small arms expert, once pointed out that every time actual military personnel give input they select a short (intermediate) round of 6.5 or 7mm (.25-.28 caliber), but always get something smaller or larger once the government pogues get their fingers into the selection.
This is a little outside my experience, but I have to wonder a little about the overall heavier weight (weapon/ammo) when we are trying so hard to integrate women into the combat arms.
One of the trends over the last couple of decades has been for US soldiers to use less ammo in fire fights. Even machine guns are often used in single shot mode. Better training and optics have made a difference. Maybe they figure not as much ammo is needed. Some of the new electronic aids especially promise significant improvements even over the present situation.