If you're going to bash McNamara over the M-16, don't forget that he refused to allow Colt to chrome line the barrel and chamber, which would have mitigated some of the fouling issues.
False:
It was Stoner, paid as a representative by Colt who told the TCC in 1963 the chrome chamber and bore was not needed. Colt was desperate for the first 508 order for 116,000 rifles and they did not want anything to delay the order. They had bet the business on it.
The ultimate problem was insufficient cleaning equipment to units that were given the rifles in Vietnam, as opposed to being deployed with the rifle and the problems of the WCC846 powder. WCC 846 had calcium carbonate added to the powder, I forget the exact percentage but it was nominally around 0.25 to 1 % by weight. In that percentage it allowed for longer barrel life in automatic fire with the 7.6 NATO cartridge. In the M16 direct impingement system, concentration higher than .75% would lead to the gas tube fouling and hydroscopic deposits that lead to rust. That oversight was fixed in 1968 and by 1970 all of the old lots were out of the system.
All of the defects the XM16E1 to M16A1 had in the first few years are typical introduction of a new technology sort of issues.