This also includes the Marine Corps statement by Gen Conway “We are never going to be a carbine Marine Corps, OK. We’re never going to go completely to the M4. We’re a rifle Marine Corps. We believe in long-range shooting skills, and those skills are just not as resident in a carbine as they are in a service rifle.” Meanwhile the Army is going full tilt with the smaller M4 and are investing a lot of money in upgrading it.
While a new 5.56 round the Special Operations Science and Technology (SOST) that is more lethal is beginning to see use in the Army's M4s and the Marines M16A4 it still comes down to a matter of ballistics. The 5.56 round in its current form is its most lethal when used from a 20" barrel rifle. While the M4 is handier in urban fighting and when having to get in and out of vehicles accuracy begins to suffer much beyond 200 meters. While not an issue in a highly urbanized country like Iraq in Afghanistan long distance shooting is a norm. The Army predicts that most modern combat will be against urban insurgents however we are in one shooting war where long range shooting capabilities is a plus.
While on the topic reliability needs to be discussed while the M16A4 seems to work well enough however the M4 has had issues. During the Battle of Wanat One staff sergeant described how his M4 failed him early in the battle. “My M4 quit firing and would no longer charge when I tried to correct the malfunction,” said the soldier, identified as Staff Sgt. Phillips in a draft analysis paper on the battle written by the Army Combat Studies Institute at Fort Leavenworth.
If I were the Sec Def I would gather my Joint Chiefs and tell them that all the services were adapting the AK model in 5.56. The 18" barrel and side folding stock will make the Army happy for compactness and the Marines still are using rifle. The Galil would work but is rather heavy AKs are being produced here in the states and production is not hard which is why the Soviets/Russians still use them. Are they a precision weapon, no, but they will run all day YES.
I personally would have a weapon that is practically accurate and not a precision tack driver.