Alternatively, the M-14 would be downscaled to carry the new lighter round, but this showed to be too difficult, or expensive. Therefore the user friendly M-16 and its offshoot were developped, although the troubles it encountered in Vietnam, first looked to downgrade the riffle, which was actually a very good weapon, but the servicemen using it lacked training to keep the weapon clean at all times. When the proper care is taken to maintain the weapon, the M-16 is an excelent and very accurate riffle.
Excuse me, but the M-16 in its early years in Vietnam probably caused the deaths of more American soldiers than the AK-47. It was a tin-plated piece of crap that wasn't worth the powder it took to blow it to hell. Have you ever tried to keep a rifle "clean at all times" in an environment that is by turns knee deep mud, dust so thick you choke on it, sheets of rain, and sun so hot gun oil drips out of the barrel? You can bury an AK in a mudhole, dig it up three days later, clear the barrel, chamber a round, and rock 'n roll. The early -16s jammed if a rain drop hit them the wrong way.
And BTW, the ability to carry more ammo so often cited as a reason for the -16 never seemed to bother 5'3" NVA troops who lugged AK-47s and its larger round.
The problem was McNamara and his "Whiz Kids." As originally designed, the M-16 was built loose enough to tolerate dirt and dust. But when it was accepted for general use, McNamara's ignorant Ivy League idiots tightened the specs to the point where the action wouldn't tolerate so much as a speck of dust. There were other problems -- badly designed ammo, lack of chroming in the right spots in the action. Put a weapon like that in Vietnam's environment and it's a recipe for disaster. Marines were punching four and five holes through attacking VC and not even slowing them down. The light-weight bullets could be deflected by leaves, for crying out loud. And more than one dead Marine or soldier was found with a jammed M-16 in his hands. It was a weapon made for draftee soldiers who were never trained in one-shot-one kill marksmanship but instead favored a "spray and pray" approach to firefights.
This was a classic case of a good -- not great, but good -- weapon ruined by desk jockeys with no real-world experience. It took at least two years and too many lives before the problems were solved. Even then, it never shook the "Mattel rifle" stigma. Iraq and Afghanistan have only reemphasized the weapon's many weaknesses, including its lack of long-range effectiveness.