Dear Jim,
The alleged failure of M4 [1]s in Afghanistan is being discussed on my forum and others. The story so far seems to be that when troops fired enough rounds [in a very short period of time] to overheat the weapons, they jammed. This is true of any weapon. Of course, circumstances may dictate that this happen, but it is not a design defect. The M4 is a carbine, not a light machineguns. It’s akin to blaming the HMMWV [2] for having bad armor, when it was designed as a light truck. This site [3] has some details, and a link to the after-action report (AAR [4]). – Michael Z. Williamson [5], SurvivalBlog Editor at Large