[EDITOR: From a DT friend (who prefers to remain anonymous) on his chop of the AWG's fight for their HK-416s]
The AWG folks are a special US Army task force to deal with IED threats that has turned into a semi-covert group of trigger pulling "trouble shooters." They got the HK416 because of their semi-official/semi-covert status and then got them taken away when Sen. Coburn both noticed this and embarrassed the Army small arms procurement brass by pointing it out.
To be fair to the Brass, they are in a no-win situation because small arms are a religious faith where true believers will not be swayed by real data.
In the realm of hard "non-religious data," there seem to be two major knocks against the M4: fouling after lots of firing, and excessive jamming in sandy conditions. Controlled tests in sandstorm-of-the-century conditions indicate the M4 is worse than the HK416 and FN SCAR, but all are in the 99-percentile reliability range.
To quote something a friend of mine sent on the issue:
"Excessive fouling depends on how many major firefights you get into before you can pull maintenance. All three systems use some sort of cylinder-and-piston arrangement to manage the gases. In the M16-type system, it's in the bolt carrier itself, while the other two restrict it to a small area near the gas port. They all have to be cleaned, eventually. The competition community has developed some M16 gas system tweaks that might interest serious trigger-pullers.
As a professional, your weapon's health comes first, just like your horse would if you were cavalry. If someone gave me one of each of these weapons, and several thousand rounds of ammo, I might develop a clear favorite. I doubt highly that I would find one totally unfit for my uses."
I have also been told that a number of M-16 jam problems would disappear if the H&K M16 magazine were adopted as standard issue. It is "...the absolute best out there. Built, and priced, like a BMW.
In the particular case of the HK416 and the AWG, Sen. Coburn would have done better by the troops by earmarking money for HK416.
Since Coburn is a Republican "Small Federal Government"/anti-earmark true believer, this was the result.
From the military procurement point of view, earmarks actually play a very important role in defense readiness in non-glamorous things like transport ships, trucks, and planes.
Rep Les Aspins 1980s earmarks of extra 10-ton HEMET trucks gave the US Army the truck transport to pull off the famous left hook in the 1991 Gulf War.
Sen Trent Lotts earmarks of amphibious ships have given the USMC 20% of its current amphibious fleet.
Former Speaker Newt Gingrichs earmarks of extra C-130s and Rep Dana Rohrabachers earmarks of extra C-17s are the wings resupplying troops in Afghanistan.
Outside of those non-glamorous areas, DoD earmarks are rightly seen as pernicious.