Many people who like the AK malign the M-16/AR-15 for reliability problems--both real and conjectured.
When the M-16 saw general service in Vietnam, a number of problems emerged that haunt the weapon to this day. First, it was issued with no cleaning kits--a major problem for any firearm. Second it did not have a chrome plated chamber or bore. This is a major problem, especially in a tropical environment because it makes the gun vulnerable to corrosion and rust as well as problems from fouling from ammo. In WWII the US Ordnance Department found that chrome plating the chamber prevented many extraction problems. The fault lies with then Secretary of Defense Robert McNamara and his so-called "whiz kids" that he brought with him. These guys had a background in business and knew nothing of small arms or the military, so in their infinite wisdom they decided not to have the chamber and barrel chome plated since the original AR-15 did not.
Finally they changed the powder in the ammo to something that it was not developed or tested with. The gun was tested with IMR powder, but since it was not immediately available in the amount needed for the ammo necessary for the number of M-16s issued, they went with Ball powder. This had two effects. First, in increased the M-16s cyclic rate in full auto beyond what it was designed for, leading to malfunctions. Second, it was a dirtier burning powder than IMR, leading to increased fouling in a firearm that did not have a chrome plated chamber and was not issued with a cleaning kit. I think you can see where this is going and where it went.
Long story short, as soon as they started issuing M-16s with chromed chambers and bores, with cleaning kits, and started using the powder that the gun was designed for the reliability problems almost vanished, providing that the Soldier or Marine took the time to clean and lubricate his weapon.
Flash forward to the Gulf War of 1990-91 and the War on Terror and Iraq conflict of the 21st century. Again we hear stories of the M4/M-16 having reliability problems. WHile it is true the M4/M-16 is not as robust in harsh environments given lack of maintenance as say an AK-47 style firearm, many of the problems are caused by lack of maintenance, lubrication, and parts replacement.
First, many problems are caused by bad magazines. Noted firearms instructor and writer Pat Rogers of EAG Tactical (http://www.eagtactical.com) reminds us that magazines for the AR are a consumable material and will eventually go bad from things like bad feed lips. This will manifest itself in things like feeding malfunctions. It is important to number your magazines and toss them as soon as they start showing problems (discerning magazine problems from gun problems is a whole different issue and beyond the scope of this entry). This is something that needs to be done on an individual level as well as unit level for the military, but it isn't often done and has only recently come to general attention. Like tires, magazines have a finite life. If they ran tires on military vehicles for 100,000 miles, no one would be surprised if they had a high level of blowouts and other problems. But they do the same thing with the M4/M-16 and act surprised that guns have problems with magazines that are obviously past their prime or have been damaged through use. Magazines, especially AR magazines, have a finite life. Interestingly, most AR/M4/M-16 malfunctions are magazine related.
The extractor and extractor spring and extractor spring buffer at least once every 5000 rounds. These parts are responsible for extraction issues. Also replace the gas rings, since they may be worn.
Here's a link to an upgrade kit:http://www.bravocompanyusa.com/BCM-Extractor-Spring-Uprade-Kit-p/bcm%20extractor%20spring%20upgrade.htm
Finally, proper lubrication: http://www.militarytimes.com/news/2007/07/army_carbine_lubrication_070716/
Hints on keeping it running, including a great 2 part article by Mike Pannone, a Veteran of Marine Recon and Army Special Forces.
http://www.ar15.com/content/swat/keepitrunning.pdf
http://new.defensereview.com/m4m4a1-carbine-reliability-issues-why-they-occur-and-why-theyre-our-fault/http://new.defensereview.com/m4m4a1-carbine-reliability-issues-part-ii-diagnosing-the-root-cause/
