As a disclaimer I was not in the military but do know a lot about rifles. I like the M4 due to it light cartridge and one can carry many rounds and if you do not have on body armor it will kill you. It will not penetrate body armor. I would think a squad of a mix of M4 5.56 and the old M14 7.62-51would be more effective than one armed with just the new weapon essentially a .270 which is an excellent round.
War dogs please comment.
MIXED AMMO is pretty much a logistical horror story, to be avoided whenever possible on the squad/platoon/company/etc. level. Yes, BMG is still used, but that’s a different matter.