My brother loaned me a recent article in Jane's Small Arms that detailed the problems encountered in the M4/M4A1, with both reliability and ammunition problems, to include the 77 gr. round. Unfortunately, the article is in Maryland, and I'm in Georgia. Those of you with access can reveiw it. It dealt with the M4 and the M14. He has no dog in the fight, considering anything less than 5"/54 cal. to be unworthy of attention.
A new, MilSpec M4 or M16A3 is reliable and accurate for several thousands of rounds. It may not be as sand-tolerant as other weapons, but it'll work. The problem occurs after the weapon begins to wear. None of us have micrometer calibrated eyes, and the early signs of failure can be attributed to any number of external factors. The usual result is a jamming problem at the odd, usually worst, time.
As for the AK, I'd like to point out that these weapons, in many cases, have been in use for decades. They were new in the 1970s and 1980s. That they are still capable of function, and hits, is a testimony to Kalashnikov's genius. I'd like to say that most of these beat-up old soldiers are still capable of minute-of-soldier after many thousands of rounds. A 30-40 year-old M16, with the maintenance given the AKs we encounter, would have reduced itself to splinters long ago.
I'll point out that the weapons issued to trainees are clean, and are given inspections by the armorers between classes. Any badly worn parts, including the barrels are replaced. I spoke to the armorers at Parris Island when my daughter graduated from USMC Boot Camp just over a year ago.