I once read an article on the problems that early M-16's had in Vietnam. It seems the problem mostly where failure to remove a spent case from the chamber and this was mostly caused by a change in powder at the last minute without timing the DI gas system to match. It seam the gas system was moving the bolt back when the case was still under pressure and being forced against the walls of the chamber, thus jamming the gun.
In other words the problems in Nam were not a inherent flaw in the design, but rather caused by a last minute change in ammo that required a change in gas system timing, which was never done.
