The Big M4 Myth: "Fouling caused by the direct impingement gas system makes the M4 Carbine unreliable."
http://www.defensereview.com/the-big-m4-myth-fouling-caused-by-the-direct-impingement-gas-system-makes-the-m4-unreliable/

M4/M4A1 Carbine Reliability Issues: Why They Occur, and Why They’re Our Fault!
http://www.defensereview.com/m4m4a1-carbine-reliability-issues-why-they-occur-and-why-theyre-our-fault/

M4/M4A1 Carbine Reliability Issues
Part II: Diagnosing the root cause.
http://www.defensereview.com/m4m4a1-carbine-reliability-issues-part-ii-diagnosing-the-root-cause/

M4/M4A1 Carbine (and AR-15 Carbine) Malfunctions
http://www.defensereview.com/an-operators-view-of-m4m4a1-carbine-and-ar-15-carbine-malfunctions/

LaRue Tactical Stealth 16-Inch Upper-Config AR Carbine: Range Report
http://www.defensereview.com/larue-tactical-stealth-16-inch-upper-config-ar-carbine-range-report/