It's also worth noting the AR-15 has been in constant military service for 50 years now, that's a lot of time to trouble shoot, and a lot more than the M1 or M14 ever got (approx. 21 years and 10 years, respectively)
Though I will add that most of the history of the M16 presented in this thread is pretty doubtful. The article linked on the AnarchAngel contains so many ridiculous claims I almost laughed out loud; the forward assist was not added to correct any jamming problems, it was there years before the jamming issue arose in 1966; the army didn't sabotage anything, at least, not after the ARPA report came out in 1962; the importance of the cleaning is somewhat true, but probably overstated; the whole powder story as popularly known has enough untruths and exaggerations to earn it's own run-on sentence. Maybe two.
Best guess is the real cause of the 1966-67 jamming controversy was a decline in quality control at Colt's, as the problems coincided with a massive increase in production, but the possibility of investigating that was missed by Ichord and there is too much water under the bridge now, we'll probably never be able to prove it.
And now something more concrete...
Report No. 26 (obtained from the U.S. Government Printing office in Washington, D.C.) - Report of the Special Subcommittee on the M-16 Rifle Program of the Committee on Armed Services, House of Representatives, Nineteenth Congress, First Session, October 19, 1967.
Quoting directly from this Congressional Report:
"That both Army and Marine Corps personnel have experienced serious and excessive malfunctions with the M-16 rifle, the most serious being the failure to extract the spent cartridge."
"That the AR-15/ M-16 as initially developed was and excellent and reliable weapon."
"That certain modifications made to the rifle at the insistence of the Army were unnecessary and were not supported by test data."
"That two of these modifications increased the unit cost of the rifle substantially and and decreased its performance characteristics. These modifications were the bolt closure device chrome plating of the chamber and the change in barrel twist."
"That the major contribution to malfunctions experienced in Vietnam was ammunition loaded with ball powder."
"That the change from IMR extruded powder to ball propellant in 1964 for 5.56 ammunition was not justified or supported by test data."
"That a number of modifications to the M-16 rifle were made necessary after ball propellant was adopted for 5.56 ammunition."
"That officials in the Department of The Army were aware of the adverse effect of the ball propellant on the cyclic rate of the M-16 rifle as early as March 1964, yet continued to accept delivery of additional thousands of rifles that were not subjected to acceptance or endurance tests using the ammunition of greatest density in the field and in the supply system (ball propellant ammunition)."
"That the Army system of development, production, and introduction of a new weapon into the inventory should be thoroughly reviewed to determine if the M-16 rifle program is typical of the manner in which the Army operates. The manner in which the Army rifle program has been managed is unbelievable."
Stoner, Sullivan and Fremont, the designers of the gun and ammunition, were not consulted before the change. It wasn't until October, 1966 that a team from Colt Industries (Colt had acquired the exclusive manufacturing rights in Dec. 59), led by 'Koni' Ito, went to Vietnam to find the problems with the M-16. The most common extraction problem was rim shear, where the extractor pulled through the rim because the fired case stuck in a dirty, eroded chamber. Also carrier keys, piston end of the gas tubes, and interiors of the bolts were rusty, dirty, and very carboned. There was a lack of lubrication of the buffer assemblies so that many assemblies were frozen which led to high cyclic rates (original rate of 850 vs 1000 after the introduction of IMR powder) and parts failures. Most magazines were dirty and bent to hell as well. The Colt team found that 40% of the magazines were unserviceable.