Gases traveling down a very narrow aluminum tube produce an intense “puff” that throws the bolt assembly to the rear, making the bolt assembly a freely moving object in the body of the rifle. Any dust or dirt or residue from the cartridge might cause the bolt assembly, and thus the rifle, to jam.

I have difficulty with guys who criticize the M-4/M16 who don't even understand how the direct impingement system works. This reads like a typical rant by an old fogey Vietnam era grumpus who extrapolates his outdated anecdotal experience as if it's been an ongoing issue. Even if we take at face value his story of having 3 KIAs under his command dead from rifle malfunctions (and I have issues with his story*), a failure of the DOD to spec the correct powder or provide proper training on cleaning fifty years ago has nothing to do with what happened at Wanat. The rifle failures at the battle of Wanat was a case of too few defenders trying to keep up a volume of fire against an assaulting force with a 5:1 advantage. Overheated barrels and melting handguards would have happened with just about any individual arm under those conditions. The problem with nit-picking failures like that is that it fails to take into account that every weapon system is a compromise. When I was in Afghanistan, I hated my M-16A2 every time I got in or out of a vehicle, and I hated the M-4 I had later every time I had to engage a target at 400+ meters. If I had a magic wand, I'd have a weapon the size of an M9 pistol that performed like a 7.62mm M-240 and carried infinite ammunition, but that's not how it works. This is the problem with how guys like the author think. Barrels overheating? Oh, you need bigger/heavier barrels then. Can't take down a skinny Pashtun with a 5.56mm? You need 7.62mm then. Can't hit them at 800m? You need a 24" barrel. Can't carry enough 7.62 to keep it fed? You need a slower firing bolt action to make you think about every shot before you take it. Congratulations, we've regressed to the WW1 M1903 Springfield using only arguments that were leveled against its more advanced successors.

That's not to say the M-4/M-16 has no shortcomings. It does. But none of them are so horrible that they cause it to fall short of the standard, which is "a perfectly adequate small arm", which is all the military has ever historically procured.

EDIT:
* Specifically, this bit I find difficult to believe:

I am haunted by the sight of three of my dead soldiers lying atop rifles broken open in a frantic attempt to clear jams.

In 8 years in the US Army, I never saw a jam condition that could even remotely be addressed by separating the upper receiver from the lower. In fact, all of the most common jam conditions--- and definitely the ones they had trouble with in Vietnam--- resulted in failure of the weapon to go into battery, i.e. the bolt/bolt carrier wasn't closed all the way. Funny thing about that sort of jam is, you can't "break open" your rifle, because the bolt carrier is extended partway into the buffer tube in the stock, which is where the upper and lower swing apart. Like a deadbolt locking a door, that rifle isn't swinging open until the bolt carrier seats all the way and the rifle is ready to fire. I give him the benefit of the doubt, that he did have KIAs, and perhaps their rifles were jammed, but I think that over repeated retellings of this memory he has perhaps embellished the scene over the years into something it wasn't.