A leaked US Army report about the Battle of Wanat criticizes the reliability of the M4. On July 13, 2008 200 Taliban fighters attacked 48 US and 24 Afghan troops. Outnumbered 2.7 to 1 the M4 Carbines, which the troops were carrying, could not function reliably under the sustained fire they were required to put downrange. Fox News reports:

The platoon-sized unit of U.S. soldiers and about two dozen Afghan troops was shooting back with such intensity the barrels on their weapons turned white hot. The high rate of fire appears to have put a number of weapons out of commission, even though the guns are tested and built to operate in extreme conditions.

…

“My weapon was overheating,” McKaig said, according to Cubbison’s report. “I had shot about 12 magazines by this point already and it had only been about a half hour or so into the fight. I couldn’t charge my weapon and put another round in because it was too hot, so I got mad and threw my weapon down.”

Snowflakes In Hell, via Michael Bane’s blog, correctly points out that assault rifles are not machine guns:

No assault rifle is going to stand up to sustained automatic fire. They aren’t machine guns, and even a machine gun needs to have its barrel changed out if it’s been firing a lot.

The M4 has a very short 14.5″ barrel and a relatively lightweight barrel profile. This allows the barrel to heat up much faster than a longer and heavier rifle or machine gun barrel. When the barrel of a closed-bolt gun gets very hot, cook-offs,when a round is ignited from the heat in the chamber, become a significant problem … not to mention the fact that a soldier cannot fire a gun that is to hot to hold!

The Marines have been criticized by many for their plans to introduce an Infantry Automatic Rifle (IAR) into the mix of weapons issued to their troops. The IAR is not intended to replace the SAW but would be deployed alongside it, giving some riflemen a light weight weapon that can sustain automatic fire.

FN IAR. Switches from closed-bolt to open-bolt when automatically when barrel temperature increases.

The Army would do well to look into the concept.

At the end of last year the Marines announced they were awarding contracts for the development of IAR prototypes to Colt, H&K and FN. Since then I have heard nothing about the IAR.

There are discussions about the M4 failure at Wanat over at Snowflakes In Hell, via Michael Bane’s blog and SaysUncle.

Many thanks to Jerry, Caedis, Lee and Lance for emailing me links about this story.