I read that the M16 Jammed because it was supposed to use a specific type of powder for the cartridges or something, but for cost reasons, the High-ups just decided to put in normal powder. Apparently, with the right cartridge, these things were pretty reliable.
A small selection of findings from the 1 June 1968 Report of the M16 Rifle Review Panel, available in volumes on DTIC here. These are from volume 1 and appendices 4 and 6 and a small part of 7, which are the only parts I have read, as this report is enormous.
Ammunition and magazines: Use of WC 846 powder caused excessive cyclic rate of fire, up to 110rpm above upper design limit (84), bolt carrier bounce and consequent light striking (101), higher pressure at the gas port and excessive fouling. (195) Excessive cyclic rate of fire contributed to failure of the bolt to lock to the rear after the last round in a magazine, which accounted for 42% of all malfunctions in a 1965 test. (appendix 6 80) A redesigned buffer alleviating the above problems (except, obviously, fouling) only entered service 1.5 years later. (appendix 6 146) Use of IMR 8208M powder also "contributed to malfunctions" (74), increasing failure rate by over 100% compared to WC 846 in two 1968 tests. (appendix 6 127, 131) Light striking from bolt carrier bounce was compounded by poor primer sensitivity. (appendix 4 22) Use of M196 tracer ammunition caused excessive fouling. (appendix 4 60) 74.3% of malfunctions in a 1967 study and 42.9% from 1967-68 "were failures to feed, a malfunction which can often be attributed to the magazine." (appendix 6 106, 117)
Mechanical: Chambers were corrosion-pitted due to lack of chrome plating in early production (e.g. 65% of a sample of Marine-issued rifles) (104). Exposure to rain in testing caused elevated malfunction rates, but not substantially more or less than other adverse conditions (extreme cold, lack of lubrication). (appendix 6, various charts) Only 0.5% of malfunctions in a 1965-66 study "were attributed to broken, damaged, inoperative, or defective parts." (appendix 6 102)
Training: Training on the M16 for units deploying to Vietnam was insufficient and in the case of some individuals nonexistent. (109, 127) "The 1st Brigade, 101st Airborne Division, the 173d Airborne Brigade, and the 5th Special Forces were the only units surveyed that had received training with the M16 for a significant period of time prior to deployment to Vietnam." Not coincidentally, "with the exception of the weapons of the 1st Brigade, 101st Airborne Division, the 173d Airborne Brigade, and the 5th Special Forces, all the weapons [in a 1965-66 survey in Vietnam] were poorly maintained." (appendix 7 6, 7) Primary maintenance faults encountered were: "excessive oil on the weapon", "carbon buildup", "overloading of magazines with 21 rounds", "oil and grit inside magazines", "lubricated ammunition" (!), and "failure to replace worn and broken extractors and extractor springs." (122) Appendix 3, which further details training problems, is not yet digitized/available on DTIC.
The first two points are the ammunition issues frequently mentioned, particularly ball-type WC 846. IMR 8208M and WC 846 powder were adopted, if I remember correctly (control+F is finicky with these PDFs), to consistently meet the maximum chamber pressure specification of 5.56x45mm while still delivering the required muzzle velocity.
Page numbers are not original and are given for the DTIC PDFs.
I hesitate to post this knowing that somebody, somewhere, is going to connect it to the same tired, Call of Duty gun expert idea that the AR-15 is fundamentally flawed and will fail to feed, fail to fire, and fail to eject on the same trigger pull if it comes within 4,000 miles of dirt or sand. Because I have just plowed through several 200-page (+/- 100) reports and appendices I am tired; therefore, I will not refute this position but will instead let WeaponsMan, Nathaniel Fitch[2], Mike Pannone, and the Ballistic Radio team, each of whom individually has forgotten more than I will ever know about firearms and their use, do so for me.
If you are so inclined, have too much free time, and are able to do so without falling asleep at your computer, I recommend reading at least parts of the report itself to get a broader context and information that I missed, omitted, or got wrong, which, if my track record holds, is all of it.
Edit: By the way, about a month after I originally posted this, Ballistic Radio successfully completed their test at 20,145 rounds with zero cleanings and zero weapon-related malfunctions (2347th round FTF due to magazine spring binding, 8582nd round FTE due to soft brass.)
