Back in the 1960's, when the US Army introduced the M16 rifle, there was enormous controversy about it.
The early models were certainly less than fully reliable. There were reports of US servicemen being found dead on the battlefield in Vietnam with jammed rifles at their sides - even with cleaning rods in their hands as they tried to get them un-jammed. Suffice it to say that many servicemen of that era developed a prejudice against the M16 rifle that has never diminished. (An outstanding two-part article about the experiences and conclusions of a US Marine expert may be found here and here - links are to Adobe Acrobat documents in .PDF format.)
A major historical document about the controversy has become available online. The 'M-16 Rifle Case Study' (link is to a .PDF file) was prepared by Col. Richard R. Hallock of the US Army in 1970. It's over 160 pages long, and goes into the development of US service rifles from the turn of the 20th century through the late 1960's, documenting not only technical information but also the 'power politics' and bureaucratic shenanigans of many players involved. It's an absolutely invaluable resource for the technical military historian.
Highly recommended reading for those interested in the M16 controversy, and as a useful case study in weapons development.