Lloyd has hit on the key with the weight of the weapon, and ammo. I have humped everything from the A2, which is now the M4, to the M14, to even the mini14, and I even once decided that a Thompson in 45acp would look good on me in the marijuana patches along the Texas-Oklahoma river bottoms. The weight of the Thompson was a real eye opener about 2 hours into the insertion.
The M4, M16, AR15, their all the same really is the best of all worlds when one puts into perspective that it was designed to hunt the thinnest skinned animal (man) on the planet.
Having put thousands of rounds thru the AR platform rifles (including the M16), AND the M14, it is hard for me to imagine the M14 being more reliable in blowing sand given the reality that the Garand action is an OPEN UNPROTECTED action. Imagine dropping it in a sand dune, and it immediately filling the action with fine sand. How long do you really think it will operate? Right now the M14 is being used in "speciality" assignments, and there is obviously time to maintain.
Maintenance is the key with any weapon, and the same number of M14s against a like number of M4s, in IDENTICAL roles with IDENTICAL conditions, I wonder how the M14 in Iraq would actually fair. Now I'm not saying I'm right, I am saying the test has not been given to determine that. There will be some that will squawk about the Vietnam transition but, that has long since been put to rest with a change of gun powders. JM2C