@TMW
I hate to repeat myself twice, and with you it goes for a 10th time.
1. A lot of times infantry does not shoot to kill, but to suppress fire. This is not sniping rifle we are talking about here, but an assault rifle. A soldier can carry less ammo with M14, because it is heavier, meaning he will shoot less, which in turn means his enemies will have the opportunity go gain a better position, while he remains in the same area, trying to snipe them under heavy fire. We are talking about real-life situations here, and before you get to think about the kinetic energy of the bullet you are shooting, you need to think as well about the kinetic energy of the bullets the enemy fires at you. Combat is NOT a honorable duel. It is chaos, and in order to control it you don't need high-caliber rifle, but a rifle that can help you suppress the enemy fire.
2. When you are going to use M14, you will carry less ammo with you. Sure, if you are talking about shooting people who just stand and wear body protection, you will probably be better of with an M14 or a sniping rifle. However, your enemy does not stand still and you need to fire to maneuver yourself and him into a position more favorable to you. In addition, very few enemies actually wear body protection, and if they wear body protection, this is your lesser concern, because it means they probably have some pretty heavy weapons with them, and if you don't have firesupport - you are fucked up.
3. And I am not even talking about your qualification regarding real-life combat.
If you want to prove your point, write down 7-10 parameters that you can measure a rifle by. Then, decide which of them gets what weight, and rate each rifle according to these parameters. Calculate the average, and you might get a beginning of an understanding what rifle should infantry use (and for what mission...)
I am not coming from the US army, and you already have 2-3 soldiers from different countries saying that your point of view is plain wrong, but you are not willing to listen. Are you arguing for the sake of argument?