The only substantive difference between the M4 and M16A4 is the barrel length (14.5" vs 20") and the buttstock (collapsible vs. fixed).
The M4 is proving wildly popular everywhere, especially with law enforcement, as it's easy to tote around and still offers much of the lethality of a rifle.
Problem is, it's not a rifle -it's a carbine. The short barrel cuts the velocity of the issue M855 considerably, and reduces not only it's effective range but also its terminal performance. Yup, they're bitching about the ammunition - ammunition which, by the way, works just fine from a standard 20" barrel. And while were on the subject, the 11 and 14.5in barreled M4s remain statistically somewhat less reliable than 20" rifles, due to reduced gas system length.
The right answer is to purchase quantities of both rifles, and issue the long guns to troops most likely to need them.
For a tanker, artillerymen or aviator, the M4 is a great rifle. For the infantryman, the 20" M16A4 is the superior choice.
Good points -- it's not rocket science:
shorter barrel = reduced velocity.
shorter barrel = reduced effective range.
They do seemed to be overlooking the obvious.
10th Mountain BUMP!
Just for clarification, the M4 (14.5" barrel) has the same length of barrel in front of the gas port as the M16A1/A2. I only shoot my M4 for fun, but I have had no reliability issues with it. Of course, my Colt commando upper (11.5" barrel) runs just fine, also.