Thursday, June 13, 2024

Biting the Silver Bullet 4: Lethality of the 5.56 NATO Caliber

By Sanjay Soni

Sanjay Soni, Managing Director of Hughes Precision Manufacturing Pvt. Ltd

In continuation to my last article on improving lethality of ammunition, let us look at the lethality of the most popular round used by NATO forces – the 5.56x45mm M855.

Before we get into that, let us examine how the 5.56 became the caliber of choice for NATO forces.

Back in the early 1950s, the fledgling North Atlantic Treaty Organization (NATO) set about looking for a single rifle cartridge that could be adopted throughout the alliance, making it easier and cheaper to procure and distribute ammunition force-wide and adding interoperability to the widely diverse military forces within NATO.

Despite some concerns about recoil, the 7.62 x 51 mm NATO round was adopted in 1954, thanks largely to America’s belief that it was the best choice available.

Left to right: 7.62 mm NATO, 5.56 mm NATO, and 9 mm NATO cartridges.

The 7.62 x 51 mm cartridge actually remains in use today thanks to its stopping power and effective range, but it wasn’t long before even the 7.62’s biggest champions in the US began to recognize its shortcomings.

These rounds were powerful and accurate, but they were also heavy, expensive, and created a great deal of recoil when compared to the service rifles and cartridges of the modern era.

As early as 1957, early development began on a new, small caliber, high-velocity round and rifle platform. These new cartridges would be based on the much smaller and lighter .22 caliber round, but despite the smaller projectile, US specifications also required that it maintained supersonic speed beyond 500 yards and could penetrate a standard-issue ballistic helmet at that same distance.

What the US military asked for wasn’t possible with existing cartridges, so plans for new ammo and a new rifle were quickly drawn up.

The Remington .222 Special and 5.56 x 45 mm NATO

In order to make a smaller round offer up the punch the US military needed, Remington converted their .222 round into the .222 Special. This new round was designed specifically to withstand the amount of pressure required to make the new projectile meet the performance standards established by the Pentagon. The longer case of the .222 Special also made it better suited for magazine feeding for semi-automatic weapons.

Eventually, the .222 Special was redubbed .223 Remington — a name AR-15 owners may recognize as among the two calibers of rounds that your rifle can fire.

Strips of 5.56 mm ammunition collected by Alaska Army National Guard soldiers during M249 light machine gun training at Joint Base Elmendorf-Richardson, Alaska, March 3, 2018. US Air Force/Alejandro Peña

That led to yet another new round, which FN based off of Remington’s .223 caliber design, that was dubbed the 5.56 x 45 mm NATO. This new round exceeded the Defense Department’s requirements for muzzle velocity and range, and fired exceedingly well from Armalite designed rifles.

Early tests showed increases in rifleman accuracy as well as decreases in weapon malfunctions when compared to the M1 Garand, with many experts contending at the time that the new rifle was superior to the M14, despite still having a few issues that needed to be worked out.

Ultimately, the decision to shift from 7.62 x 51 mm ammunition to 5.56 x 45 mm came down to simple arithmetic.

The smaller rounds weighed less, allowing troops to carry more ammunition into the fight. They also created less recoil, making it easier to level the weapon back onto the target between rounds and making automatic fire easier to manage. Tests showed that troops equipped with smaller 5.56 mm rounds could engage targets more efficiently and effectively than those firing larger, heavier bullets.

As they say in Marine Corps rifle teams, the goal is to locate, close with, and destroy the enemy — and the 5.56 mm NATO round made troops better at doing precisely that.

Is there a problem with the lethality of the 5.56mm caliber?

This is not a simple question to answer.

We will discuss the benefits of the 5.56mm NATO caliber, compare it with its bigger brother 7.62, look into effects of barrel length and finally how to improve the lethality of our soldiers.

As I stated in my last article, there are two ways to incapacitate an enemy:

  • Hit to the central nervous system. This is the brain and upper part of the spine. It will cause immediate incapacitation regardless of caliber or type of bullet.
  • Loss of blood pressure by massive bleeding. This area corresponds to the rest of the central body and incapacitation can take time. Hunters aim for the lungs and heart when they hunt. A deer shot right through the heart can run quite some distance.

Soldiers are top priority within NATO and the soldier’s primary weapon is his rifle.  To use it effectively he must be well trained for any possible encounter with the enemy and it is very important that he “trains as he fights.”  In his final training there must be pop up and moving targets at unknown distances.  He must be under stress and be able to respond immediately.  

There has been small arms lethality discussions within NATO for several years, but to clarify things once and for all a NATO Workshop on Small Arms Lethality was hosted by the United Kingdom in February 2009 at their Defence Academy in Shrivenham.  The conclusion was that shot placement is the most important parameter, and that this is achieved through good and realistic training.

There are two major problems with current and future soldier systems: weight and power supply.  Individual soldiers can carry 60 kg (132 lbs) into operations. This includes weapons, ammo, body armor, water, etc. Many nations are trying to lighten soldiers’ load incrementally by lightening each new item during new procurements. 

Most accessories use batteries. These are often of different sizes and have different life expectancies. NATO is currently studying several industry solutions of a powered rail system, where the power is centralized in the pistol grip or buttstock and is sent to the rails where the flashlight, for example, would only consist of a reflector. This reduces weight and volume of the device and increases battery life expectancy.

The Belgian small arms producer FN Herstal – formerly FN (Fabrique Nationale d’Armes de Guerre) developed a weapon family in the mid 70s consisting of the FNC rifle and the Minimi LMG (light machine gun).  To increase the range for the LMG, a round that could penetrate the NATO plate (3.5mm mild steel) out to 600m was developed.  It had a dual core (steel tip and lead rear), and was designated M855 or SS109 and required a one in nine inch rifling twist.  There was no requirement to penetrate body armor.  The L110 tracer round however required a fast one in seven inch rifling twist.

In 1970, NATO decided to try and standardize a common rifle and a second rifle caliber. During 1977-1980 NATO therefore performed tests with rifles and ammunition.  

The calibers tested were:

  • 5.56mm rounds with increased penetration from

Belgium (FN SS109) and USA (XM777)

  • A British 4.85mm round. This was a necked down

5.56mm cartridge

  • A German 4.7mm caseless round

However, no weapon could be agreed upon as many of the weapons were prototypes. The SS109 round was found to be the best, and was standardized as NATO’s second rifle caliber in 1980.

One quite often reads of the benefits of 7.62mm over 5.56mm. The truth is, however, most of the time the opposite.

The benefits of 5.56mm over 7.62mm are:

  • Equal lethality against unprotected enemies
  • Half the mass (12g – 24g)
  • Half the volume
  • Reduced recoil and signature (noise and flash) that

allows for a faster second shot

  • Better penetration in thin metal plates
  • Flatter trajectory and shorter time of flight out to 700m
  • Lighter weapons
  • Higher hit probability

A higher hit probability is possible when the soldier is not afraid of the recoil and noise, and can concentrate on his stance, weapon control, aiming, and trigger pull.  Several nations have reported this when they changed from 7.62mm caliber to 5.56mm.


The benefit of 7.62mm is that it has more energy.  The impact energy of the 7.62mm is more than twice of the 5.56.  If the target is not protected, that energy level is not really needed.  A 5.56mm or 7.62mm ball round will normally pass right through an enemy all the way out to over 600m.


NATO realizes that different nations spend time and ammunition for training differently, and expect soldiers to perform to different levels of marksmanship.  This resulted in Spain hosting a NATO Workshop on Marksmanship Training.  The results showed that only few nations teach shooting to ordinary infantry soldiers beyond 200-300m.  

The reason nations do not teach their soldiers to shoot at longer ranges is that it is very difficult to hit at longer range due to:

  • Shooter’s dispersion
  • Moving targets
  • Unknown range
  • Wind drift

Swedish units in ISAF rely on 12.7mm HMG for long range.

Let us look at a comparison between 5.56mm and 7.62mm with equal barrel lengths (20-inches – 508 mm):


As can be seen, 5.56mm has a flatter trajectory.  So now let us compare a 5.56mm M4 barrel (14.5 inches) with a 7.62mm long barrel (20 inches).  They are identical.  There has been some debate that the “short” M4 barrel is the cause of some “lack of lethality” issues.  This is simply not true.  The same thing applies to time of flight for these.

 This is an important issue because it affects the required target lead when engaging moving targets.

Let us look at some interior ballistics.  With caliber 7.62, the barrel is typically around 20 inches (508mm).  The bullet will have 50% of its velocity within 80mm (3 inches) of travel.  If you shorten the barrel you will lose some muzzle velocity, and you will increase the muzzle pressure (noise and flash).


To scientifically investigate the effect of barrel length and muzzle velocity the Spaniards took a brand new Colt M16A2 barrel and cut it down in 30mm increments and measured the velocity.  They used NATO reference ammunition, fired at +21° C.


The effect of a long barrel has often been greatly exaggerated. The trajectories for the M16 (20-inch barrel) and M4 (14.5-inch barrel) resulted in a difference of only 16 mm (0.6 inch) when zeroed at 250m.

The difference in time of flight is also very low, only 2 cm (0.75 inch) per meter per second of traverse target movement at 300m.  An enemy normally walks at 2m/s and runs at 5m/s.

Looking at the data, one can assume that the 5.56 is as effective as a 7.62 round at distances between 150-400 meters. However, in reality that is not so. The issue is with the lethality of the 5.56 M855 round in actual combat.

Many have criticized the 5.56mm round as lacking sufficient terminal effectiveness in combat. Combat veteran and military small arms expert Jim Schatz explains that “the disturbing failure of the 5.56x45mm caliber to consistently offer adequate incapacitation has been known for nearly [twenty] years.” He describes one Special Forces (SF) mission in Afghanistan when an insurgent was shot seven to eight times in the torso, got back up, climbed over a wall, and reengaged other SF soldiers, killing a SF medic. The insurgent then was shot another six to eight times from about twenty to thirty yards before finally being killed by a SF soldier with an M1911 handgun. 

Schatz knows experienced law enforcement snipers who no longer use .223/5.56 sniper rifles even if they can shoot superior non military hollow-point projectiles “because this cartridge is simply not considered an effective ‘one-shot man-stopper.’” Rob Maylor, a former Australian SAS sniper, has “on several occasions witnessed bad guys being hit multiple times by 5.56mm . . . at varying ranges and then continue to fight.” He explains that while the 5.56mm round is designed to yaw and fragment, “this isn’t happening all the time and as a result projectiles are passing through the body with minimal damage. The bestselling book Black Hawk Down gives vivid accounts of the less-than-lethal performance of the Army’s green-tip 5.56mm bullet (M855) in the Battle of Mogadishu in 1993.

In my interview with several army men from the Infantry, they universally complained about the inadequate stopping power of the 5.56 round. They have witnessed this first hand in actual combat against Pakistani soldiers and Kashmiri terrorists; wherein the enemy has sustained 5.56 round hits but still continued fighting with little impairment in their fighting abilities. The enemy has been able to effectively retaliate despite getting hit and cause damage to our soldiers. Therefore, the infantry is veering towards adopting a heavier round like the 7.62 notwithstanding the limitations we talked about earlier.

5.56mm vs. 6.8mm

There has been longstanding debate within the military community about which caliber round is most effective in combat. Based on data from more than 10,000 test shots at various distances with multiple caliber rounds, the 2006 U.S. Joint Service Wound Ballistics Integrated Product Team (JSWB-IPT) concluded that the optimum caliber for terminal performance is not the 5.56mm round but the 6.8mm round. 

The next generation of combat rifles likely will use a more effective intermediate caliber round between 6.5 and 7.0mm rather than the smaller 5.56mm round.

Sanjay Soni is the Managing Director of Hughes Precision Manufacturing Pvt. Ltd., India’s first small caliber manufacturer in the private sector. An MBA from the Indian Institute of Management, Bangalore, he has been involved with the ammunition industry in India and abroad since the last 8 years.


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