Designing a weapon that will work accurately and reliably in every type of combat condition is problematic at best.
A weapon designed to be extremely accurate requites that barrel, stock, and receiver be fitted tightly with little play between each. An automatic weapon built to such a standard, such as the original M-16, will be prone to jamming from sand, grit, mud, and cold under battlefield conditions.
A weapon built to somewhat looser tolerances, such as the AK-47, will work reliably and be far less prone to jamming under similar conditions. Yet, the AK is a far from satisfactory weapon for engagements requiring extended range and accuracy, a battlefield venue for which the M-16 or M-14 is more aptly suited.
There doesn't seem to be a middle ground here. Either you can meet one set of requirements at the expense of the other, or vice-versa, but definitely not both. The only solution to meet the varying needs is to train the troops in the use of both types, and issue the suitable equipment when conditions call it, i.e., when troops are about to enter into street-sweeping combat, or open-field operations.