My own suggestion would be to go to an AK type weapon. With one M-14 per fire team, for long-distance work.
If that is too complicated, then just bring back the M-14.
Surprise, surprise. The .220 Swift, and the milder .222, of my youth (the former almost identical to the .223) were wonderful on varmints and worthless on large game (not even allowed in many jurisdictions). When I was in the AF and we heard that the Army was going to get a smaller caliber weapon than the M-14, stupid me, I thought they were going to get something like the 6.5X55 Swedish Mauser, or my personal fav, the .257 Roberts, either of which is extremely accurate, easy to shoot, and can knock down a whitetail buck at very long range. But no, they got the M-16, an apparently lesser version the AR-15 in use by the AF at the time for Police and Security work. If I were in Afghanistan (or Iraq), where long range shooting is required, I think I would join you and opt for the M-14: something like a scoped version of the Springfield Armory Civilian Version or one of those Police Sniper rigs they sell. The .308 can kill at 500 meters for sure, and in a sniper's hands, is lethal out at a 1,000.
In their bureaucratic quest to perfect the M-16, the Army have taken away automatic fire in favor of 3-shot burst capability ( a good idea), and they have made it increasingly heavier. Right now, it comes in at 9.5 pounds ... same as an M-1. The problem is there is no way to make a 70-grain bullet reliably lethal at 500 yards. Naturally, the SAW has the same problem. (BTW, this round is also easily deflected by brush or grass)
Lessons learned? Bring back real guns and ammo. The M-16 in .223 is a street sweeper, simply not a weapon for wide open spaces. Use it to equip REMFs and women.
Then the troops would KNOW satisfaction.
My own suggestion would be to go to an AK type weapon. With one M-14 per fire team, for long-distance work.
If that is too complicated, then just bring back the M-14.
Sigh.......
The M16 probably needs to Move On... But, it's just too bad Stoner and Kalashnikov aren't around any more, now that the Cold War is over. We could just give the two of them a billion-dollar budget and tell them to agree on a solution to all our problems.