A friends AR-15 hate got me thinking about my personal experiences with it so I thought I would share what I think the main issue is with the "lack" of reliability so many note from combat theaters.
A little of my background:
I joined the Marine Corps in 2009 right before the "surge of troops" into Afghanistan. I was an 0311 (rifleman) and 0313 (LAV crewman).
I did two deployments (both 7 months) to southern Helmand that spanned the years 2010, 2011, and 2012. During this time I got to intimately know my M4 carbine and what it took to make it run.
Here are the two main problems that I and other troops I knew ran into (none which were the weapons fault):
1) Lack of training on how to properly lubricate the weapon system for a desert environment.
This is the major issue I ran into really quickly when I first arrived in country. I had been told by a SGT to hardly lube my gun because it would cause malfunctions because of the dust it would gather. I quickly learned (during a gun fight unfortunately) that a dry bolt simply does not run and that spitting on the bolt is a ineffective method of making the gun work(I hadn't of thought to bring CLP with me). From that point on I heavily lubed my bolt and carried extra lube on me and promptly spread the word not to listen to that Sgt's knowledge. I still saw this lack of lubrication practice later on in my deployments and to my dismay was usually told I was an idiot for voicing my opinion on the matter. What was worst is I commonly heard a lot of these same guys cursing their bolt action carbines during after action reports.
*its important to note that a lot of us were against heavily lubing our rifles in the states because it would cause us to have to spend more time cleaning our weapons to turn them into the armory. IMO this is a huge flaw in the system, troops should be taught to heavily lube their weapons with a little less emphasis on inspection ready cleaning.
2) Bad magazines.
I was issued six magazine when I first got to my unit, all very old with very old springs. Those promptly got replaced by pmags until it was decided that those were unsat by someone.. So I was regulated to carry the old magazines that often caused double feeds (which was a common theme among my buddies as well). We resolved this by replacing the magazine springs with any newer ones we could scrounge up but its still a issue we should of never ran into.
*also another important note. Even though Pmags are still banned before I left new magazines and extra followers were dished out. So it seems at least the old followers and springs have been addressed for the most part.
Just are just my thoughts on the subject, I hope other people will throw in some of their ideas on why people perceive the gun as unreliable and how its not a hard ware problem, but a software issue.