The M4 Carbine’s Uncertain Future

In honor of Veterans Day it seemed appropriate to discuss a firearm that is relevant to our military. The M4 Carbine has been in service since the early nineties. Anyone that has served in the U.S. Armed Forces from the Vietnam era on is likely familiar with this gun, or one of the other rifles in the M16 family of firearms. We will take a look at the features and background of this infantry carbine, but also explore some of the controversy that surrounds its future as a primary service weapon.

Ground troops in the Army and Marine Corps are equipped with a standard issue M4 Carbine, and in certain capacities it is assigned to troops throughout the Navy and Air Force as well.

The sleek M4 is a 5.56mm caliber lightweight, magazine fed, shoulder fired, close combat weapon. This carbine weighs just over seven pounds when fully loaded with a thirty round magazine, and features a short 14.5” barrel and a telescoping stock that measures just 33” when fully extended. Designed for versatility the M4 incorporates a flat top receiver and Picatinny rail system that allows for individual customization. A variety of add-on equipment can be mounted to the firearm to suit the individual soldier’s needs with little sacrifice of its close combat prowess. These accessories can include, but are not limited to night vision devices, M26 MASS shotguns, and M203 under barrel grenade launchers.

It features an air-cooled, gas-operated, direct impingement system. This action utilizes the gas generated from a fired cartridge by venting it through a thin aluminum tube attached to the barrel. This produces an intense force of gas pressure that makes direct contact with the bolt carrier at the opposite end of the tube to cycle the action. The direct impingement is a simplified and lightweight design that keeps all recoiling parts of the gun in line to help preserve the sight focus during rapid firing. However, a disadvantage to this system is that it can accumulate foreign matter in the bolt area as the gas emissions condense, requiring frequent cleanings to assure proper operation.

No change to the direct impingement has taken place on the M16/M4 platform, but these guns have continued a trend of retrofitted improvements in many other areas. Some of the modifications included upgrading the barrel and trigger, and the addition of ambidextrous controls.

Early M4 models included a selective fire control that featured options for semi-automatic and three round burst. The burst mode was abandoned on the newer M4A1 Carbine and replaced with a full automatic fire setting. A change in the selective fire function has also alternated with each of the four M16 full-length rifle generations.

The M16 is the base of the platform and was the military adaptation of the Armalite Rifle (AR-15) that was engineered by Eugene Stoner back in the late fifties. In the early stages of the military adoption, the rifle was designated as the XM16E1 and incorporated the very first modification - a forward assist feature not originally included on the AR15.  The modification was added at the government’s request. This was the earliest M16 variant placed into service during the Vietnam War.

The rifle offered many of the characteristics that the military was looking for at the time, as they moved to replace the M14 and the few aging M1 Garands that were still in service. It was lighter and delivered far less recoil than either of the other two rifles, and it offered the full auto select fire feature with a twenty round magazine.

The XM16E1 rifles sent to Vietnam were widely criticized for their inability to stand up to the harsh elements and demands of combat. The Army received countless complaints regarding jamming and malfunctioning during its introduction period. Although nothing could be done to eliminate the muddy and dusty terrain, the military did take steps to remedy the initial concerns with the rifle. They made a switch to a cleaner propellant powder in the 5.56x45mm cartridges to reduce build up in the bolt from gas emissions and they chrome plated the bores of the next waves of rifles to be sent to troops. Satisfied that this appeared to remedy the situation, the improved version was soon standardized as the M16A1. It went on to officially replace the M14 as the U.S. Military standard service rifle in the late sixties.

Nearly twenty years after its introduction the second generation M16A2 would feature several more modifications. Among these were the addition of a case deflector and ergonomic improvements to the handguard, pistol grip, and butt stock. It was also the first change made to the trigger group; the military did away with the full auto function in the A2 and replaced it with the three round burst feature. A move likely geared towards conserving ammunition and increasing accuracy of the shots fired.

Even though two more generations of the M16 were yet to come, this is the point where the M4 Carbine came to fruition. Based upon the M16A2, Colt produced the smaller XM4, which would later be designated by the military as simply M4. The carbine held over eighty-percent commonality with the larger service rifle, but offered some notable differences such as the shorter barrel and telescoping stock.

The first M4 carbines began slowly entering service in the early nineties, but as conflicts escalated in the Middle East, post 9/11, the Army and Marine Corp accelerated the issuance of the weapon for use by ground troops.

Since then the reviews of the carbine have been somewhat mixed. While a number of troops have praised the versatility and reliability of the M4, other feedback has not been quite as positive. According to an article written by Rowan Scarborough in the Washington Times back in 2014, an independent survey was conducted among soldiers returning from Iraq and Afghanistan. Twenty percent of these soldiers reported that the M4 jammed during battle and a fifth of them stated that the stoppages made a large impact on the outcome. These issues were reminiscent of those reported with the first XM16E1 fifty years earlier. This riled some critics of the platform and although most acknowledge that the carbine possesses some great attributes, they feel that we can do better for our troops.

One of the most outspoken voices against the continued use of the M4 in the infantry is retired U.S. Army Major General Robert H. Scales, who by his own account experienced the M16 debacle first hand while commanding troops in Vietnam. This past May he was afforded the opportunity to speak in front of the Senate Armed Services Committee where he outlined his grievances with the current infantry carbine. His full Statement for the Record is readily available to the public online.

Two main deficiencies that Major General Scales pointed out were with the direct impingement gas system and the stopping power and range of the 5.56 caliber.

He advised the committee that the infantry should be equipped with a firearm that utilizes a gas piston system rather than the vulnerable direct impingement. Noting that a piston system would move a solid operating rod and the bolt as one unit, something akin to the Soviet AK-47 or the HK-416. He explained that the solid attachment of a piston system would prevent debris from jamming the action and would require less frequent field cleaning. A flaw in the direct impingement system that he claims has contributed to a staggering number of unnecessary deaths over the years.

The piston system has also earned the trust of others in the military. Special Operation units such as Delta Force and SEAL Team Six have already added the Heckler & Koch carbine to their arsenal to replace some of the M249 Light Machine Guns. In 2011 the HK-416 variant (Military designation M27) gained notoriety as the gun that the SEALs used to take down al-Qaeda leader Osama Bin Laden. The argument that the Major General makes is that if top-tier units such as these recognize the need for a more reliable weapon, than so should those in charge of arming our front-line troops.

The other main issue addressed was the inefficiency of the 5.56 cartridge during combat. A round that was developed by Robert Hutton, and Eugene Stoner for the AR-15 in an effort to meet the military requirement of reducing recoil to allow for automatic fire. During the testing phase this ammunition managed to meet the stringent demands of velocity and helmet penetration at 500 yards, but it would never possess the knockdown power of the 7.62x51 NATO or the .30-06 Springfield calibers that it ultimately replaced. Nevertheless, the smaller round impressed the decision-makers thanks in part to Stoner’s rifle trials. It would later become the basis for the popular varmint sporting round .223 Remington, and after modifications to the projectile and loading it would eventually be officially adopted as NATO ammunition. However, the Major General and other critics believe it is just simply too small for modern combat.

The replacement that Scales suggested would be between 6.5 and 7mm with a lightweight casing. Presumably something close to a military adaptation of the .270 Winchester sporting caliber, which would provide a much longer range, medium recoil, and suitable stopping power.

It’s hard to say if Scales input has made enough of an impact to help move the infantry rifle to the top of the acquisition list, but at the very least he gave them something to consider.

It is nearly certain that one day the M4 and M16 will become idle like the rifles that preceded them, and be stock piled in some warehouse alongside the Springfields, Krags, and Garands; but their place in our military history is already assured. There is little doubt that as technology advances, there will be more modular and far more effective infantry weapons produced. Those too will likely be both praised and criticized; although, the true test of any infantry firearm’s success will be tallied in the number of our troops that return home safe from battle.

As civilians we cannot truly fathom the confidence and trust that a soldier must place in their rifle. So although we can evaluate its engineering and viability from afar, those who carry it into harm's way should always be the primary judges of its adequacy.