Saturday, 19 July 2014

The Great Internet Calibre debate, part 1,651,198....

If you want to kick off a lively discussion on a military based website then you have several choices. Aircraft carriers are one. Inter-service rivalries are another. Probably the grand daddy of them all though is to talk about gun calibres with respect to service rifles. It can get very heated at times.

The problem with such discussions is that it's very easy to make an unsupported assertion based on "common knowledge", but it takes a long time to systematically refute such arguments in the sort of detail that is required to satisfy even casual observers who have no dog in the fight. It's almost impossible to turn a "believer" against their chosen opinion, even with large quantities of what is practically irrefutable data.

One of the reasons I started this blog was so I could essentially write such responses in one place and then in future just drop a link to save myself much typing. Today I'm going to do just that for the infantry calibre debate, something that if you include underlying research I've been working on now for many years.

The Sturmgewehr 44
To understand why we've arrived where we are now with the NATO standard 5.56mm calibre round you have to go all the way back to the war of 1939-1945. Much study of this conflict would later inform decision making surrounding the adoption of the 5.56, but for now there was one major change that took place which would set the course for the future.

The German Sturmgewehr 44 is widely accepted as the worlds first true assault rifle. Combining the ability to hit targets out to around 500 yards with individual shots in a semi-automatic mode, as well as the ability to fire rapidly in fully automatic mode (almost 600 rounds per minute) the StG 44 represented a bridge between short ranged sub-machine guns and longer ranged bolt action rifles.

Despite its 1944 designation the concept and early development behind the weapon had begun even before the war. Investigations by the German General staff of the 1914-18 war had identified that most infantry actions rarely took place at ranges over 800 yards, which was significantly shorter than the maximum range of the standard Mauser Model 1898 rifle.

In essence the full power round being fired from a 29-inch barrel was a complete waste. A shorter weapon firing a less powerful round would still be able to cope with the vast majority of infantry engagements while providing a lighter weapon and permitting a greater amount of ammunition to be carried. 

The smaller, lighter weapon would come in the form of the Karabiner 98k, but this was still a bolt action weapon with a limited magazine capacity. In 1938 work began to find a replacement with higher magazine capacity and a higher rate of fire, which would eventually lead to the introduction of the StG 44.

The new weapon had obvious advantages. It could still engage individual targets out to the upper end of the most commonly encountered ranges. Importantly it could also be used as a suppressive weapon when a nearby machine gun was reloading, in effect becoming a light machine gun. In the close assault it could suppress enemy positions while other soldiers threw grenades and in urban combat it was small enough and had sufficient firepower to act as a substitute for a sub machine gun.

All in all the StG 44 was a well rounded weapon and a trend setter. The trend was quickly adopted by the Russians with their AK-47, but it would take the Western nations a little longer to catch on.

Project ALCLAD
After the second world war the US army began conducting research to help it learn the lessons of its previous campaigns, as well as preparing it for potential future threats. As part of this effort it began to contract the services of the Operations Research Office (ORO) of the John Hopkins University in Baltimore, Maryland, for help in conducting the scientific analysis of various aspects of ground warfare.

On October 1st, 1948, the ORO began Project ALCLAD, a study into the means of protecting soldiers from the "casualty producing hazards of warfare". In order to determine how best to protect soldiers from harm, it was first necessary to investigate the major causes of casualties in war.

After studying large quantities of combat and casualty reports, ALCLAD concluded that first and foremost the main danger to combat soldiers was from high explosive weapons such as artillery shells, fragments from which accounted for the vast majority of combat casualties. It also determined that casualties inflicted by small arms fire were essentially random.

Although the main purpose of this study was to analyse methods of protecting soldiers in the future*, the research that went into the study laid the ground work for a later project; Project BALANCE.

*For those that are interested - and I know this has been a much debated topic for soldiers serving in Afghanistan - Project ALCLAD concluded that body armour (aside from a good helmet) was largely a waste of time for infantrymen. The weight of the armour necessary was considered to be too limiting on the mobility and combat effectiveness of the soldier.

On the 12th February, 1951, the ORO began Project BALANCE. This project was designed to study weapon effectiveness and to make recommendations about the optimum nature of various weapon systems for ground warfare, including the standard issue infantry weapon.

As part of this study BALANCE looked at battlefield visibility. One of the reasons that infantry engagements often take place at such short ranges is simple; there are very few places on Earth where you can actually see in a straight line for more than about 1,000 yards. 

Having taken around 18,000 readings of terrain in Canada, France, Germany, the United States, Korea and North Africa, it was demonstrated that a prone infantryman would be be able to see an erect human target at no more 300 yards in 70% of the readings, and at no more than 700 yards in 90% of the readings.

Even on what appears at first to be very flat, featureless terrain (such as in the desert), the contours of the land will restrict visibility markedly. Tank crews had a similar problem, being rated a 1% chance of detecting an enemy tank at 2,000 yards and facing a maximum practical visual limit of 1,000 yards for 90% of the time.

Thus the nature of sight lines coupled with the efforts of enemies to protect themselves by using cover and concealment, along with the use of armoured vehicles to cross open terrain, severely hampers the ability of soldiers to locate and engage one another with small arms at anything other than relatively short distances.

The researchers also went back and re-examined the casualty data from Project ALCLAD. It had been noticed during this study that the distribution of injuries around the body from small arms fire was almost identical to that of fragments from exploding bodies, or in other words "aimed" small arms fire was in fact no more accurate than the randomness of a nearby mortar round.

Further to this, study of the more specific circumstances surrounding injuries from small arms fire demonstrated two key trends. Firstly, that the level of exposure to incoming fire was the main determinant in how likely a person was to be hit and where such a hit would land. Aimed fire had almost no impact on wound distribution.

Secondly, that large quantities of ammunition expenditure were required to achieve each hit, and that as the amount of rounds fired went up, so did the number of hits. This can best be visualised by imagining throwing darts at a dart board. Even someone who is a poor darts player will eventually hit the bulls eye if they throw enough darts at it.

Perhaps more worrying for marksmanship fans was that BALANCE looked at two other (external) studies, one from Normandy in world war two and the other of Turkish soldiers wounded in Korea, that showed that most hits were received at ranges of less than a hundred yards.

Two additional studies were reviewed to collect further data about weapon usage. One was a British study of weapons usage in Europe during the second world war and the other was a study done by the ORO itself of soldiers in Korea. Both studies - conducted independent of one another, by two different teams, on two different sets of soldiers, who fought in two different theatres of war - produced a remarkable degree of agreement; that 80% of rifle and light machine gun fire was conducted at ranges of less than 200 yards, and 90% at less than 300 yards.

All of this data matches the pre-war German investigations that lead to the StG44 and as such lead the Project BALANCE researchers to a similar conclusion; that the M1 Garand rifle and its ammunition were massively over powered for the typical ranges at which infantry combat actually took place.

But in order to learn more about the influence of marksmanship, particularly accuracy at different ranges and under stress, the Project BALANCE researchers decided to run a trial at a firing range at Fort Belvoir, Virginia. 32 soldiers were used in the experiment, 16 of them rated as being "Experts" (the highest marksmanship rating at the time) and 16 were rated "Marksman" (the lowest qualified grade). All used the M1 Garand from the prone position for the tests.

They were split into groups and asked to shoot at static Type E targets (a head and torso target 20 inches wide and about 40 inches tall) at ranges of 110, 205, 265 and 310 yards. They shot first individually, then in groups to simulate some of the noise and distraction of battle. Targets were exposed for three seconds during which one shot was taken, then hidden for three seconds, then exposed again and so on and so forth until each man had fired 8 rounds per target (4 for the group firing).

At 110 yards the accuracy for both groups was pretty good, in particular the experts. But at just 205 yards the experts were already missing around half of their shots. The marksman, as you might imagine, did even worse. At 310 yards the experts barely managed to hit the target with one third of their shots. When firing in groups the average accuracy dropped even further.
The third stage of the test saw 4 marksmen and 4 experts tested on a variation designed to induce greater stress through time pressure. Here two targets (110 yards and 265 yards) were exposed for just one second at a time, in a random order unknown to the shooters, for a total of 8 shots (one shot per exposure).

I think you've probably guessed this already, but suffice to say that the accuracy fell off a cliff even at the closer range, being more comparable to the 310 yard results from the earlier tests. Oddly enough though it was the marksmen that did slightly better, though probably luck had as much role to play in that as skill given the low number of hits.

A number of significant conclusions were thus drawn from these tests. Firstly, that accuracy - even for prone riflemen, some of them expert shots, shooting at large static targets - was poor beyond ranges of about 250 yards. Secondly, that under simulated conditions of combat shooting an expert level marksman was no more accurate than a regular shot. And finally that the capabilities of the individual shooters were far below the potential of the rifle itself.

This in turn - along with the analysis of missed shots caught by a screen behind the targets - led to three further conclusions.

First, that any effort to try and make the infantry's general purpose weapon more accurate (such as expensive barrels) was largely a waste of time and money. The weapon was, and probably always would be, inherently capable of shooting much tighter groups than the human behind it.

Second, that there was a practical limit to the value of marksmanship training for regular infantry soldiers. Beyond a certain basic level of training any additional hours were of limited value*, and the number of hours required to achieve a high level of proficiency would be prohibitive. This was particularly of interest for planning in the event of another mass mobilisation for war.

Although no suggestion was put forward as to why this is the case, it is likely caused by the fact that experienced, high quality shooters derive much of their advantage on a firing range from the time taken to line up a shot carefully, control the trigger, etc. Under the time constrained conditions of battle these measures are seldom practical.

*Please note this is not an argument in favour of little or no marksmanship training, merely that the law of diminishing returns appears to kick in very quickly when it comes to the practical level of marksmanship that can be expected under conditions of or approaching those experienced by combat soldiers.

Lastly, that poor accuracy could potentially be overcome by designing a weapon that fired a salvo of several shots at the same time. Using the missed test shots as a guide it was calculated that a weapon that fired either a 4 or 5 round diamond shaped group (the 5 round group would have one round in the middle), with a 20 inch dispersion at 300 yards, would more than double the hit probability for most soldiers.

In the case of this salvo weapon the researchers made the point that this was more of an idealised concept, acknowledging that such a weapon would be difficult to manufacture and require a significant ammunition load, something which they were trying to avoid.

It was also mentioned that if future technology permitted it then probably the best weapon would be something akin to a grenade launcher that was able to fire rounds with timed fuses, such that the grenades would detonate right over the enemies head and practically guarantee one or more hits.

On a more practical note another test was ordered, this time run by the army, to see if a rapid fire weapon could produce the necessary dispersion without the added complexity. The test at Fort Benning, Georgia, using then contemporary automatic rifles firing large calibre, full power rifle rounds was not a success. In fact it demonstrated that they were completely uncontrollable in fully automatic bursts and that aimed single shots would be more effective, even at close range.

And so it is that we come to the 5.56mm/.22 inch round. Rounds of this calibre had been available for many years, but it was only around this time that Remington made the first commercial rimless .22 cartridge. The Project BALANCE researchers identified this calibre as having the potential to be used in a lightweight firearm that would have sufficiently low recoil to allow firing either rapidly in semi-automatic mode, or in short automatic bursts, in both cases trying to create something approximating the type of dispersion desired.

It's important to note here that when discussing possible designs the researchers emphasised that "the chief point of concern, however, is to strive for the attainment of the pattern dispersion principle so that the greatest possible gains can be derived..." [underlining original]. In other words the concept was more important than the specific application, and as such whatever solution could achieve the closest results within the engineering and financial constraints would be satisfactory.

It was also recognised, as consistent with earlier evidence, that simply the ability to fire more single shots at the same target would increase the likelihood of a hit. If a soldier can hit a plate at 300 yards with only 25% of his shots then on average you would expect him to have to fire at least four shots at it to guarantee a hit. Giving him more ammunition and a lower level of disturbance between shots should increase his chances of hitting the target within a given time window.

One further concern, one that was not covered by BALANCE, is the issue of suppression. The experience of all sides during the second world war demonstrated the value of being able to suppress or "beat down" an enemy with concentrated, high volume small arms fire, forcing the enemy to take cover and thus hindering their movement, observation and ability to fire.

It is broadly accepted that there are two key aspects to effective suppressive fire (snipers excluded); accuracy and volume. The more accurate the fire is, the more of a danger it poses, while the more rounds coming in, the less time in between shots the enemy has to take a peek over the parapet so to speak. With certain weapon types the volume of fire can also affect how well distributed the fire is over a given position.

As we have seen above accuracy under combat like conditions is likely to be poor beyond short ranges, while high powered rifles are generally unsuitable for sustained rapid fire. In the modern context the light machine gun (LMG) generally offers infantry sections/squads the suppressive capability required, as the volume of fire possible also compensates for the inherent inaccuracy of the human using it.

But there are still two significant problems to be solved. Firstly the need to cover for the LMG when it's reloading and secondly to compensate for when the enemy line is dispersed over a wide area, such that the LMG can only cover a small part at any one time. To cover these circumstances it would be desirable for the main infantry weapon to be capable of suppressive fire, at least to an extent.

And this is where small calibre weapons come into their own again. Either firing rapid single shots, or short automatic bursts, a small calibre rifle offers the ability to generate reasonably accurate volume fire on an enemy position without imposing a prohibitive weight penalty on the infantryman.

Now just to come back to Project BALANCE for one last point before we move on, one thing that the researchers made clear is that this was a study to help find a better general purpose infantry weapon and that its conclusions did not abrogate the need to have a small number of longer ranged weapons at the section/squad level.

This often becomes a point of contention when talking to people about small calibre vs large calibre weapons. Advocating for a small calibre, general purpose rifle should not been seen as a stance against any kind of longer ranged weapon. The conclusions of BALANCE support this and identify that niche that exists.

It's important quickly to note that we're talking here about an individual or designated marksman within the infantry section/squad as opposed to the entirely separate role of dedicated, fully trained snipers.

The advantage of having one or two soldiers who are better than average shots, and as such are trained and equipped to exploit this ability, is that the section or squad retains the ability to engage precise targets on its own when needed, even out to ranges of 500-600 yards, while also having a source of more accurate fire support during heated engagements.

The US Marine Corps for example has introduced the Squad Advanced Marksman Rifle (SAM-R), while the US infantry leans on the Squad Designated Marksman Rifle (SDM-R), both of which take the base M16A4 platform and then add better optics, a bipod and a new 20-inch barrel, among other upgrades. 

Here in the UK, the L86A2 with 25-inch barrel plus a bipod filled this role, till being replaced recently by the L129A1, a 7.62mm weapon with just a 16-inch barrel. This does seem an odd choice, given that whatever the small merits may be of the slightly larger round, the weapon is now completely incompatible with the ammunition of the rest the section, something which the US squads have avoided.

Project SALVO and Project NIBLICK
Heading into the mid-1950's the US began a series of projects, which included SALVO and SALVO II, and Project NIBLICK. SALVO was aimed at investigating - surprise, surprise - the potential for salvo firing weapons that could produce the desired dispersion as recommended by BALANCE. NIBLICK was primarily about investigating the potential for a grenade launcher, again as recommended by BALANCE.

The two main areas of investigation for SALVO were multiple bullet loads and flechette rounds.

The multiple loads came in the form of duplex and triplex rounds. In a duplex round, two small bullets are stacked one on top of the other inside the same cartridge. Triplex rounds obeyed the same principle, but obviously with three rounds now stacked inside the same cartridge. After firing the rounds would separate and travel to the target in close proximity. 

Unfortunately there were two issues with the concept. Firstly the rounds did not disperse as was planned, striking within just a few inches of one another even at longer ranges. Secondly, the small rounds made the accuracy problem worse, not better. Triplex loads have the same problem, only worse still.

Flechettes initially had much greater promise. A flechette has quite low mass so recoil is typically lower. The high speed at which they travel means that they have a much flatter trajectory. The long, thin design offered excellent penetration of helmets and other protection. And the weapons themselves proved capable of very high rates of fire.

However there were a number of down sides that ultimately did for the poor flechette. 

In order to shoot accurately they have to be stabilised as they travel along the barrel, which requires some kind of discarding sabot design. As well as making them expensive to manufacture this also posed a hazard to nearby allies when firing, as the sabot pieces would be expelled from the barrel in all directions at very high velocity. These weapons also suffered from a large muzzle flash and loud report.

A more critical flaw was the accuracy. The light flechettes were very vulnerable to the effects of wind and even heavy rain. When they reached the target they also had a tendency to deflect off if they didn't strike point first. At the end of the day flechette weapons proved impractical and subsequent experiments to try and solve these problems have so far proved fruitless.

NIBLICK had a little more success. Although many of the combined grenade/flechette weapons submitted proved to be too heavy, or too complex, the work on the grenade elements led eventually to the development of the M79 40mm launcher, and later the M203 which became the benchmark for modern under slung grenade launchers. 

The advice of BALANCE to try and produce a time-fused grenade however appears to have fallen on deaf ears. Only recently with the development of the Mark 47 launcher, a crew served weapon, has an attempt been made to create such a round.

The M-16
With the failure of SALVO and NIBLICK to produce a practical dispersion weapon it was back to the drawing board. At this point people started taking the concept of a small calibre (.22 inch) weapon seriously once more. It had only taken ten years for the military to finally act on the main recommendation of BALANCE!

And as it turned out it was the US Air Force (USAF) that made the first move in adopting the AR-15, soon to be M-16. The army was going to take some convincing. What followed was a saga of delays, mistrust between the army and the manufacturer, and even a bit of lobbying by the NRA (so the stories go).

It wasn't until more comprehensive testing was done, including a demonstration that showed that 8 men with M-16s could easily out shoot 11 men with M-14s that people really started to sit up and take notice. Problems with poor ammunition plagued the early models, but ultimately the M-16 and its later descendants would go on to prove their worth.

The issue that really plagues modern day small calibre weapons, or at least the debate about them, is the question of lethality, with lethality being defined as "the quality of being deadly".

The main problem with this part of the discussion goes back to what I said at the start about it being easy to make casual assertions without evidence and it taking a long time to prove such assertions incorrect. All too often you hear claims about "stopping power", "terminal energy", "lethality", etc. which come without a shred of evidence to back them up, a problem that is further compounded by a number of myths and legends that have become "common knowledge".

This typically starts with an assertion about the 7.62mm NATO round being a "man stopper", the insinuation being that if you can hit a man with one of these then he won't get back up again. Ever.

If that's the case then someone has some explaining to do. To go back to ALCLAD and BALANCE for a moment, one thing that was brought up from studying the small arms casualties from the second world war was that only around 30% of those hit would actually be killed. 

Bearing in mind that the Germans were firing a 7.92x57mm round out of the 24-inch barrel of the Karabiner 98k, or the same round out of the 21-inch barrel of the MG 42, then there would appear to be a problem; that's a larger, more powerful round from a longer weapon than the FN FAL/L1A1. One shot, one kill? Hmm.

Interestingly what ALCLAD had discovered was something that tallies with all the modern evidence that has been collected about firearms injuries over recent decades; that the location and number of hits was the prime determining factor in whether the injuries were fatal, not what calibre was fired.

Fundamentally most bullets kill people by causing blood loss (head and certain spinal shots being the obvious exceptions). All the theories about energy dump, remote wounding/hydrostatic shock etc, none of them to date have any proven basis in medical science. 

There is some sketchy evidence that very high velocity rounds (exceeding 2,500 feet per second at impact) can create pressure waves that may cause additional, very minor injuries (such as bursting of some capillaries) beyond the raw damage of the bullet itself, but it should be noted that a) there's actually no conclusive proof that the bullet is even causing this, and b) as far as fatal or even incapacitating gunshot wounds go, the injuries are irrelevant.

Back to blood loss then.

Basically as the bullet passes through the target it's doing damage, carving a path through skin, muscle, tissue, blood vessels and so on. The loss of blood caused by these injuries causes blood pressure (systemic arterial pressure) to drop. If it drops too low then oxygenated blood can no longer be pumped to the brain (global cerebral ischemia) which subsequently causes cells in the brain to gradually die. The quicker blood is lost, the quicker this process occurs.

Clearly then the size of the round does matter to a degree. A larger round will cause more damage. But the problem with arguing for the superiority of a 7.62mm round or a 6.5mm round etc. is that the difference in size is fairly minimal. 

As the round will tumble through tissue - typically at least (or close to) a 180 degree revolution within the depth of a human torso - then the length of the bullet, not so much the width is important. The M118 7.62mm bullet is 1.31 inches long, or about 33mm. The M855 5.56mm bullet is 0.906 inches long, or about 23mm. The difference between them, length wise, is just one centimetre. 

That's obviously better, but not by a huge amount. Certainly it's not a game changer. The location and number of hits is. 

A bullet that strikes someone in the hand will do damage, but the blood loss from it is unlikely to be particularly severe, especially if the wound is treated quickly. A bullet that passes through a major perfused organ such as a kidney or the liver is an entirely different matter, as is a bullet severing an artery.

At the same time it should be relatively straightforward to see the connection between multiple hits and increased blood loss. If you hit a kidney and sever an artery in the arm then the rate of blood loss rises dramatically. At close ranges this has always been the advantage of controllable, rapid fire weapons like sub machine guns and small calibre rifles. The ability to inflict multiple hits in quick succession dramatically increase the probability that the target will die.

That's providing of course you can actually hit the target. The old saying "a hit with a 22 is better than a miss with a 45" might be a cliche, but like most cliches it became that way for a reason; because it's true. A bullet that misses does no damage whatsoever. One that hits at least has a chance. And as we've seen above, the ability to fire as many rounds as rapidly as possible with as low a recoil as possible significantly increases your chances of actually hitting something.

But can a 5.56 deliver the fabled one stop shot? 

Well the problem with arguments about one stop shots is that again we come back to bullet placement. One of the great firearms myths is that if you produce a powerful enough round then it will be able to knock back (or knock down) someone who is charging towards you. The simple physics of that problem mean that in order to achieve this with the raw kinetic power of a bullet then you're going to need a very large bullet travelling at tremendous speed (or a small bullet travelling at eye watering speed).

The recorded history of "one stop shots" contains a variety of tales. Many are simple head shots. Many involve the bullet striking and damaging the spinal column, often not killing but causing paralysis (as happened to Nidal Malik Hasan, the 2009 Fort Hood Shooter*). Sometimes a shot in the hip can cause sufficient damage to bring someone to the ground, but without killing them. In a number of cases psychological stress has been cited as the reason, including gunshot victims who have started hyperventilating through panic and effectively knocked themselves out.

*That particular shooting is an interesting study in the effects of gunshot wounds. Nearly all the fatal victims were shot either in the head or chest. Most of those who survived were shot only in the limbs. None of those hit appear to have suffered any kind of "hydrostatic shock", despite being shot at point blank range with a 5.7mm high velocity pistol, muzzle velocity approximately 2,000 ft/s.

On the other hand there are numerous examples of people who have been riddled with bullets during the course of a gunfight and still kept going. Typically this happens when the rounds fail to strike a target of significant value, such as multiple shots that miss the arteries and major organs, but has even included people shot in the side of the face at close range with large calibre pistol rounds. Even with arterial hits though, we still have to consider the fact that blood loss takes time, it's not an immediate process.

Or in other words, the main problem with "one stop shots" is in fact the unrealistic expectations that most people have.  The simple reality is that shooting small pieces of metal at someone is an extremely inefficient way of killing them. The only reason people do it instead of using say, a sword, is because a man with a gun will nearly always win a sword fight. 

If you're expecting to kill your enemy first time every time by firing a small piece of lead into their torso then you have some serious re-evaluating ahead of you, unless that piece of lead happens to be from a .50 BMG, and even then there are absolutely no guarantees.

So why stick with the 5.56mm instead of moving on to something like a 6.5mm or 6.8mm or what have you? Simply put there's very little to actually be gained, despite the significant financial outlay that would be required. 

The increase in killing potential will be marginal at best. The increase in mechanical accuracy will be marginal and doesn't address the major weak link in the process; the human being behind the weapon. The increased recoil makes any kind of rapid fire less accurate. Ammunition capacity in the magazine vs the 5.56 is lower, as is total ammunition carried for a given weight (or more weight for a given number of rounds). Most of these new bullets are also optimised for performance at longer ranges, which is precisely the sort of place where very few military engagements actually take place. 

To put it into slightly clearer terms; they're worse than the 5.56 at all the things that have shown to be important and they're better than the 5.56 at all the things that have shown to be unimportant. Probably the best thing you can do if you want to make a real improvement is to simply make a 5.56 round that has a slightly longer bullet. 

Or, more controversially, make an even thinner, lighter round...


  1. Book marked for those days when I forget the names of the studies

  2. Given the findings of the report quoted, it's interesting that you don't really discuss the XM25 CDTE or the British attempts at an intermediate cartridge with the EM-2. The XM25 is a bit expensive as it is, but it's an interesing idea that fulfils the suggestions of BALANCE and NIBLICK.

    1. Hello Tom,

      This article was more focused on the general purpose rifle, whereas I think the XM25 is more likely to serve in the future (presuming it ever becomes widely adopted) as a squad/section level weapon like the Minimi. Initial reports seem quite promising for it though, if a tad expensive.

      I left aside EM-2 because inevitably the US preferred cartridge size was going to set the tone for the future and because the background behind EM-2, as in the research that led the designers there, is less well documented.