The Army Is Once Again Looking to Replace the 5.56mm Cartridge

The U.S. Army is once again looking into what it would take to replace the venerable 5.56mm cartridge and weapons that use it like the M16 and M4. Kickstarted at a time of major firearms developments across the U.S. military, it’s still not clear whether the new plan will succeed where previous efforts have failed.

In May 2017, Army Times revealed that the Army was working steadily on a replacement for the M16 family of weapons, along with a new cartridge for whatever gun came next. The service reportedly hopes to have a prototype or prototypes ready by 2020.

“Right now the platform we have is a workhorse and very effective in the hands of a trained soldier or Marine,” U.S. Army Major Jason Bohannon, in charge of the lethality branch at the Maneuver Center of Excellence at Fort Benning, Georgia, told Army Times. “Our next investment will likely be in a new operating platform.”

Bohannon and others are still trying to determine the specific requirements for the new gun and settle on a caliber. Army officials will be able to really get to work once the results of the Small Arms Ammunition Configuration study are ready. The service expects this work, which has been going on since 2014, to wrap up no later than August 2017. There a lot of ideas already out there, though.

US Army

Decades of debate

At the core of the existing research is the long-standing search for a so-called “intermediate cartridge,” and an associated rifle or shortened carbine, which would give average troops the ability to perform well at both long- and short-ranges. After decades of existing studies, the Army shifted from historically employing guns shooting .30 caliber and 7.62mm bullets to the M16 and its .223 caliber projectile, later known formally as the 5.56x45mm. An intermediate round would be one that sits, size wise, in between these two standards at somewhere between 6mm and 7mm.

When the M16 entered service, the over-arching belief at the time was that guns firing a smaller round, and more of them, would have less recoil and therefore be more accurate. The Army had also considered small darts called flechettes and cramming multiple bullets into single cartridge cases to improve hit probability.

US Army

There  was considerable evidence that lightweight projectiles would reliably tumble,  fragment, or otherwise create horrific wounds, more than making up for  their relatively small size. On top of that, the lighter cartridges simply meant that troops could carry more ammunition, again helping making up for any loss of power compared to older designs. In addition, experience in World War II and the Korea War suggested that, on average troops engaged the enemy at relatively short ranges and that relative training and experience would have generally precluded them from doing otherwise.

“The average effective infantry fire with weapons lighter than the machine gun was consistently less than 200 yards,” U.S. Army Brigadier General S.L.A. Marshall, then acting as a historian and combat analyst, noted in a 1951 report on infantry operations and weapons usage during the Korean War. He could find no example of American troops ever bringing an enemy force to a halt with rifle and carbine fire alone.

On paper at least, the M16, with a rate of fire of approximately 750 rounds per minute, and its cartridge, officially useful out to a maximum range of 600 yards against a specific enemy, seemed to fit most of these requirements. In theory, individual soldiers could take aimed shots using the rifle’s semi-automatic firing mode, while automatic riflemen could provide suppressing fire in full-automatic. Despite near legendary teething problems during the Vietnam War, the rifle went on to prove its worth in the short-range combat of Southeast Asia’s jungles.

US Army

5.56mm fares poorly in Afghanistan

Fast-forward to the mid-2000s and there were rumblings in the Army that things had changed based on combat in Afghanistan and Iraq. Insurgent snipers and long-range weapons teams, along with the threat of manually-detonated improvised explosive devices (IEDs), reinvigorated the debate over the M16 and its caliber. These experiences are the clear impetus for the Army’s latest development.

Study after study seemed to point to the specifics of the 5.56mm cartridge as a major limiting factor. In 2006, the Joint Service Wound Ballistics–Integrated Product Team released a report that suggested a projectile between 6.5mm and 7mm was the ideal bullet size. Three years later, then-U.S. Army Major Thomas Ehrhart, wrote a now often-cited paper at the service’s Command and General Staff College, which referenced this and other research and called for a new, standard infantry weapon.

A U.S. Army soldier with a refurbished M14 rifle., US Army

“While the infantryman is ideally suited for combat in Afghanistan, his current weapons, doctrine, and marksmanship training do not provide a precise, lethal fire capability to 500 meters and are therefore inappropriate,” Ehrhart contended. “There are several ways to extend the lethality of the infantry… A better option to increase incapacitation is to adopt a larger caliber cartridge, which will function using components of the M16/M4.”

In Afghanistan more so than Iraq, insurgents employed Soviet-era 7.62x54mm SVD rifles, RPGs, recoilless rifles, and mortars and seemed to routinely out-range American squads armed primarily first with M16s and then the shorter M4 carbine. Though handier for close-quarters combat and when getting in and out of vehicles, the M4’s 14.5-inch barrel only reduced the terminal impact and effective range of the 5.56mm bullet.

Things were bad enough that troops had taken to firing expensive Javelin anti-tank missiles at enemy fighters in order to hit them from a safe distance and get at them behind hard cover, such as rock outcroppings and earthen barriers. Both the U.S. Marine Corps and the Army, along with special operations forces, initially built specialized designated marksman versions of the weapon, before beginning to reissue larger 7.62mm NATO rifles. In addition, the Army obtained a number of Mk 48 Mod 0 machine guns, a 7.62mm relative of the 5.56mm M249 Squad Automatic Weapon, and sent them to units Afghanistan. More dramatically, the service dug out Vietnam War-era M67 recoilless rifles and rushed them into service, all while pouring money into other hard-hitting explosive weaponry.

New bullets

When it came to new standard infantry weapons and cartridges, the Army, Marine Corps and U.S. Special Operations Command all punted, choosing to develop an further improved 5.56mm cartridge, which was by far the cheaper and simpler option. All three groups had entered the Global War on Terror using the already updated M855 cartridge, a heavier Belgian design featuring a steel penetrator tip for increased armor penetration.

“The muzzle velocity required for M855 to be effective is not achieved when this round is fired from the M4Al Carbine due to its 6” shorter barrel,” the U.S. Navy explained in one 2009 contract document relating to a purchase of new Mk 318 rounds for special operators and Marines. “Not only has the military’s primary weapon changed since the time M855 was fielded so has the threat target.”


However, highlighting the very active nature of the debate, the Navy still reported that the majority of engagements in Afghanistan were occurring at 100 yards or less. The Mk 318 had a new 62-grain bullet specifically designed to bust through cover, including car windows and house doors without losing too much velocity, breaking up, or tumbling wildly in the process. The round also featured better effective range from the M4’s shorter barrel, but this was a relative upgrade over the poor performance of the M855 in the gun rather than an overall increase.

A complete M855A1 EPR cartridge and the bullet itself., US Army

It’s important to note that the special operations community had previously obtained a dedicated long-range round, the Mk 262, with a significantly heavier 77-grain projectile, specifically for marksman rifles. This round subsequently filtered out to the regular services, too. Various other specialized rounds for certain tasks and training purposes also came into service.

The Army chose to craft an updated version of the M855. Critics slammed the somewhat controversially named M855A1 Enhanced Performance Round (EPR) of getting its improved characteristics at the cost of exerting almost dangerous amounts of wear and tear on M4s and other guns. Army officials attributed the worn out barrels and broken bolts mainly to quality control problems as production of the new rounds ramped up, claiming they had been resolved by the end of 2011. The round remained in service as of 2017.  

A U.S. Army special operator moves out during a sniper competition., US Army

Existing alternatives to 5.56mm

As with previous reviews, Small Arms Ammunition Configuration study will undoubtedly recommend finally abandoning these incremental improvements to the 5.56mm round and instead adopting a new intermediate cartridge.

“The term ‘old’ has an entirely different meaning in the world of small arms,” Mike Friedman, then director of Logistics for the Army’s Project Manage Soldier Weapons, told the service’s reporters in 2014. “Small arms weapon systems don’t share the same obsolescence cycles as some products like electronics or computers do. Age is not the yardstick, performance is.”

This is hardly the first time the Army, or its sister services, have toyed with the idea of a standard infantry weapon, along with other guns, firing an intermediate cartridge. There had been a particularly notable attempt to create a 6x45mm universal machine gun during the late 1970s that was both light enough to be a squad automatic weapon and powerful enough to perform as a light machine gun. Ultimately, the Army decided to field the 5.56mm M249 and keep larger machine guns, such as the M60 and M240, in 7.62mm.

A U.S. Marine Corps special operator fires at a target during a sniper competition., US Army

As of 2017, the Army and SOCOM were actively considering a slew of new cartridges, but primarily for long- and short-range work. The War Zone has already written extensively about the .300 Blackout round and its applications for close-in combat.

Then, on May 4, 2017, the Army put out a contract notice looking for suppliers of .338 and .300 Norma Magnum rounds, likely as part of SOCOM’s Advanced Sniper Rifle (ASR) program. A precision rifle in one of these calibers – or able to quickly switch between – would offer additional range and terminal benefits over existing weapons chambered in either .300 Winchester Magnum. The guns would also have extended range, but still be relatively light and compact when compared to larger weapons such the .50 caliber Barrett M82 and M107. With those characteristics in mind, General Dynamics had earlier designed a prototype .338 Norma Magnum lightweight machine gun as a possible replacement for the iconic .50 caliber Browning M2 in certain roles.

Army officials told Army Times that SOCOM was also evaluating smaller precision rounds that are popular in the civilian target shooting community, including .260 Remington and 6.5mm Creedmoor. These rounds “stay supersonic longer, have less wind drift and better terminal performance than 7.62 mm ammunition,” U.S. Army Major Aron Hauquitz explained to the reporters.

The special operators are looking at the Army Marksmanship Unit’s in-house .264 USA, as well. Defense contractor Textron previously pitched the idea of using cartridge in everything from carbines and light machine guns, akin to the old 6x45mm universal round. One of the company’s own internal studies boasted the round had “terminal effects greater than 7.62 mm NATO out to 1,200 meters,�� according to Army Times.

US Army

Money is the real factor

But in spite of this flurry of interest and development, it’s not entirely clear why the Army believes this concept is more likely to gain more traction now than it has in the past. Just by itself, the service can point to a number of stalled-out projects, including a push to include an intermediate cartridge as part of an most recent abortive attempt to upgrade or replace the M4, which ended in 2014.

More so than anything, the ultimately factor in any decision is likely to come down to cost. Replacing hundreds of thousands of standard infantry weapons and buying millions of rounds all new ammunition is a massive and expensive undertaking. In the last 75-years, the Army has done it exactly twice, first when it switched from the .30-06 Springfield to the 7.62mm NATO cartridge for standard infantry rifles and then when it moved from the 7.62mm round to the 5.56mm ammunition when it adopted the M16.

A prototype squad automatic weapon that fires cased-telescoped ammunition., US Army

The service then became the driver of similar shifts throughout the U.S. military. And the transition was by no means quick in either case. By the 1970s, one could still find second- and third-line units in the Army and its reserve components, especially those in combat support or rare non-combat functions that still necessitated small arms, using older 7.62mm M14s. By the 2000s, there were still enough M14s in storage to convert to designated marksman rifles for American troops and ship overseas to foreign allies, including the Baltic States of Estonia, Latvia, and Lithuania. The Army would have to be entirely sure that the benefits are worth the costs and complexity of such a decision. Just look at how long it took the Marine Corps to find an argument for purchasing even a relatively small number of new 5.56mm rifles

In the past, the Army has rejected the idea of adopting any new traditional metal-cased cartridge in favor of work on polymer-cased, cased-telescoped, and caseless ammunition. Cased-telescoped rounds involve nestling the bullet inside the cartridge case with the propellant to reduce overall length, while caseless rounds dispense with this disposable container for the gunpowder altogether. In theory, these options offer reduced weight, the elimination of the need to buy metal to make casings, and revolutionary shapes that could lead to radically new small arms designs. In spite of decades of near constant work, they continue to be prohibitively expensive and unreliable.

Experimental cased-telescoped, above, and caseless ammunition., US Army

The push to have the weapons ready by 2020 might be another problem. In April 2016, U.S. Army Major General Walt Piatt, head of operations, readiness and mobilization, within the service’s top headquarters’ G-3/5/7 office, said that was when he wanted “the entire Army to be fully ready – manned, trained and equipped.” These comments referred to a loss of overall readiness in the face of budget cuts and other uncertainty imposed by the process known as sequestration. At the time, Piatt said only a third of his forces were adequately prepared for combat.

Though President Donald Trump has made increasing the Pentagon’s overall budget a priority, there are concerns about how and when his funding proposals could pass through Congress. The U.S. government continues to operate on short-term continuing resolutions with the ever present fear of a shutdown over domestic political issues. The Army will have to weight just how much it wants to and actually can spend on small arms development as it also tries to update its armored vehicles, helicopters, and other major equipment.

In short, while the results of the Army’s Small Arms Ammunition Configuration study and any prototype guns that emerge as a result of its recommendations may well become the latest rallying cry for critics of the 5.56mm, it may still not be enough to move the U.S. military bureaucracy to act.

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Joseph Trevithick Avatar

Joseph Trevithick

Deputy Editor

Joseph has been a member of The War Zone team since early 2017. Prior to that, he was an Associate Editor at War Is Boring, and his byline has appeared in other publications, including Small Arms Review, Small Arms Defense Journal, Reuters, We Are the Mighty, and Task & Purpose.