^ What I have been told, the rifle (M16) was well received it was just felt the 5.56 rd to be underperforming at the longer ranges and higher cross winds that a 7.62 NATO round handled better. I have also yet to meet a Brit that calls his rifle a "FN", always L1.[/QUOTE
that's counter to a lot of first hand comments I've read back when I was a "student" of everything I could find to read or watch concerning the Vietnam war. Numerous pic were printed back then of troopers lying dead beside their Mattel's with the pins pulled trying to get the obstruction out of them so they would work (very similar to the Indian's reports of Custers soldiers found with a trapdoor beside them with an empty case in it and a ramrod in the bore) . The problem, at the time was attributed to the tight tolerances Colts machined them too, no clearance room for any dust or foreign material. The problem was so prevalent that Communist battlefield pickups were a very sought after weapon for the "bush" grunts ( Until the Brass issued orders against their use when some of the "doctored/booby-trapped" ammo that they were supplying the Cong with showed up in their own soldiers mags).
The troopers finally did learn to be prudent with the extra care required to keep the 16's as clean as possible so they would remain operational but I know a lot of vets held a grudge against the M16, claiming their malfunction directly caused the death of their buddies.
A couple years ago, Guns & Ammo reprinted several articles they ran on the M16 rifle back in the 60's (they were in an issue of Book of the AR-15). Back then, there were 3 major problems identified in '65 and '66 with the M16, only one of which could be traced to the rifle's design.
The first problem was the propellant (powder). IIRC it was Winchester Olin who couldn't make enough of the low-fouling powder the M16 was supposed to use, so the US military substituted standard ball powder that was used in the 7.62 NATO round (so the production would be enough to supply the soldiers). Standard ball powder caused much more fouling than the other powder, and we all know what fouling does to reliability.
The second problem was training. There was very little training (something along 10 hours) on the M16 before the soldier was sent to Vietnam with it. Not only did they not know how to properly clean and maintain it, they weren't even issued cleaning gear

because the rifle was promoted as "low-maintenance" (and with the original powder maybe it was) and didn't NEED cleaning (how anyone could swallow that is beyond me).
The third problem, and the only real design fault, was that the chamber and barrel were not chromed to resist the effects of fouling and corrosion. Once that was done, reliability jumped way up.
To its credit, the US military recognized these problems (after quite a bit of bad press re : casualties) and set about fixing them. The rifles' barrels and chambers were chromed, training time was more than doubled (to something around 26 hrs before the soldier went to 'Nam), cleaning kits were issued, and the powder was changed to the original spec.
There was a survey done of combat soldiers in Vietnam in late '68 about the M16 rifle. IIRC of some 2,600 soldiers surveyed, only 35 or so wanted to see the M16 replaced. 32 of those 35 or so wanted to have it replaced with a shorter version - the CAR-15 (the ancestor of the M4/C8 carbines).
Once the initial teething problems with the M16 were fixed, the soldiers came to love its light weight, speedy round, and ability to carry lots of ammo for the same weight. As an aside, the article from '65 said that an M16 with 120 rounds of ammo weighed the same as an unloaded M14-right around 9 pounds. That's a rifle and 6 loaded magazines (the US used 20 round mags at the time) for the weight of the previous rifle unloaded. As any soldier knows, ounces equal pounds, and pounds equals pain!!!