The Washington Times has a lengthy article on shortcoming and defects with the M-4 carbine. It states, in part:
Army Senior Warrant Officer Russton B. Kramer, a 20-year Green Beret, has learned that if you want to improve your chances to survive, it’s best to personally make modifications to the Army’s primary rifle — the M4 carbine.
Warrant Officer Kramer has been dropped into some of the most ferocious battles in the war on terrorism, from hunting Islamists in the mountains of northern Iraq to disrupting Taliban opium dealers in dusty southern Afghanistan. He was awarded the Silver Star for his bravery in Operation Viking Hammer to crush the terrorist group Ansar al-Islam in Iraq.
The warrant officer said he and fellow Special Forces soldiers have a trick to maintain the M4A1 — the commando version: They break the rules and buy off-the-shelf triggers and other components and overhaul the weapon themselves.
“The reliability is not there,” Warrant Officer Kramer said of the standard-issue model. “I would prefer to use something else. If I could grab something else, I would.”
Documents obtained by The Washington Times show the Pentagon was warned before the Afghanistan and Iraq wars that the iterations of the M4 carbine were flawed and might jam or fail, especially in the harsh desert conditions that both wars inflicted.
U.S. Special Operations Command in 2001 issued a damning private report that said the M4A1 was fundamentally flawed because the gun failed when called on to unleash rapid firing.
In 2002, an internal report from the Army’s Picatinny Arsenal in New Jersey said the M4A1 was prone to overheating and “catastrophic barrel failure,” according to a copy obtained by The Times.
The test findings also carried ramifications for the regular Army. By 2002, soldiers were carrying thousands of the conventional, light-barrel M4, of which the service ultimately would buy nearly 500,000 and send them into long wars in Iraq and Afghanistan. The M4, at times, has been called upon to perform the same kind of rapid fire as the M4A1.
... In 2011, a decade after the Sept. 11 attacks, the Army announced that it was converting M4s to the commando version with a heavier barrel and automatic trigger firing.
Some of the problems uncovered in 2001 and 2002, such as stoppages or jamming, became evident in the conventional firearm, most infamously in the 2008 Battle of Wanat in Afghanistan in which nine U.S. troops lost their lives.
“Realistically speaking, there’s been loss of life that is unneeded because there was a dumbing-down of the weapon system,” said Scott Traudt, who advised the Army on how to improve the M4 a decade ago.
... Mr. Traudt said he thinks the jamming problems encountered by a significant segment of troops over the past decade could have been avoided if special operations continued developing Green Mountain’s Reliability Product Improvement Kit.This is not something new to the M4. All American service rifles in the last century (and probably before) have had "teething" problems. Some have been with manufacturing (e.g., the Springfield M1903, which had problems with the heat treating of its receivers), design (the M14 had many issues when it was first introduced which was one of the reasons for the rapid adoption of the M16 in the first place), and cartridges (the cartridge for the Springfield M1903 was completely redesigned). In fact, most firearms go through a similar process of refinement as companies improve designs and address problems.
The kit was tested at the Naval Surface Warfare Center in Crane, Ind., in 2001 and at Picatinny in 2002. It included replacing the extractor spring, ejector spring, gas tube and gas plug with more heat-resistant ones, and moving to a one-piece, four-coil system that was engineered from more thermally durable materials to make the gun function better.
“An M4A1, when equipped with those parts, will fire continuously on full-automatic magazine after magazine until its barrel disintegrates,” Mr. Traudt said. “In our tests, M4A1 barrel failure occurred at 1,375 rounds. A normal Army M4A1 is out of action at 840 shots fired when equipped with its standard, metallurgically and technologically antiquated parts — and this isn’t even barrel failure. It’s gas system or bolt failure.”
At the time of the tests, internal reports by SoCom and Picatinny said the M4A1 was terribly flawed and not suited for commando missions.
But I also think the article is beating a dead horse. The reports upon which the Washington Times relies were written over 10 years ago. Many of the reliability issues have been addressed, as discussed in this 2010 article at the New York Times. The author of the NYT's piece, while embedded with troops in Afghanistan, looked at this very issue, and wrote:
The reliability questions interest me most, for two reasons. First, a rifle’s range and lethality are moot points if the rifle will not fire when a soldier needs it to fire. And second, effective range and lethality are related in part to allied cartridge choice for all NATO forces and to bullet composition — two decisions that are beyond a manufacturer’s purview.
So far this year, the photographer Tyler Hicks and I have spent roughly three months in the field in Afghanistan with American troops, many of whom are engaged in some of the most regular and intensive fighting of the war. As part of our work, we have been observing rifle performance and querying soldiers and Marines about their experiences in combat with what is arguably the most important piece of equipment they carry.
The question before us was simple: How do the reliability complaints about M-4s and M-16s we hear in the States line up against what we see and hear in the field, where the war is being fought? Put another way, could we verify the troops’ reported dislike of the rifle because of its reliability, and demonstrate the nature of any problems behind the reported disaffection?
The answer was a surprise: The M-4 and M-16 were not seen to be suffering from reliability problems, at least not among people whose paths have crossed ours.
Simply put, in observations in many firefights in harsh conditions, and in the experiences of Army and Marine grunts queried this year, the issue of rifle reliability seems much less pressing than it has appeared in accounts of widespread worries about or dislike of the M-4 and M-16.
... To be equally clear, no sample of 100 or so grunts is enough to settle any longstanding argument. But after years of carrying an M-16 (the A2 version, in the 1980s and 1990s) and years of observing them in the field, often in firefights, I have yet to see a modern M-16 or M-4 fail in the ways described in others’ reports, and I have not found significant reliability complaints from troops using the rifles in trying environments. (Interestingly, two Web sites that closely follow military equipment decisions, www.military.com and www.defensereview.com, reported late last month that the special operations community had dropped its program to replace M-4s with a rifle colloquially known as the SCAR, in part because the SCAR was not living up to its early billing – a common trait among rifles in development – and because it was not regarded as offering an upgrade on the M-4 that was worth the investment.)