The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC)

© Anthony G Williams

This is a revised and extended compilation of several presentations, including to: the National Defense Industries Association (NDIA) Joint Armaments Conference in Dallas, May 2010; the Defence IQ Infantry Weapons Conference in London, September 2010; and the Small Arms and Cannons Symposium at the UK Defence Academy, August 2012.

Selected slides from the PowerPoint presentations are included: the full set of NDIA slides is available on their website HERE

Last amended March 2014


The conflict in Afghanistan, with its emphasis on targeting specific enemy individuals while avoiding collateral damage, has demanded the use of weapons of high precision and limited destructive effect. As a result, infantry small arms acquired a much more prominent role than that expected in conventional high-intensity warfare and this highlighted the performance of their ammunition to a greater extent than ever before. Now that several NATO nations have started the process of defining their requirements for the next generation of small arms, this is a rare opportunity to ask the question: is the present combination of 5.56 and 7.62 mm rifle and machine gun cartridges optimal, or could we do better in the next generation?

The British Army analysed several hundred small-arms engagements in Afghanistan during the late 2000s. The results are thought-provoking. Ever since World War 2 around 300 metres has been regarded as the normal maximum range for small-arms engagements, but this has not been the case in Afghanistan where ranges have been much longer. Apart from the ubiquitous and rather short-ranged AKM carbines, the Taliban are equipped with PKM light machine guns and SVD sniper rifles chambered in the old but powerful 7.62 x 54R Russian cartridge, and more than half of their attacks were launched from ranges of between 300 and 900 metres.
As the fighting progressed there were indications that the engagement ranges in Afghanistan if anything became longer: THIS article in the American Rifleman states that: "U.S. Army data....reveals that more than half of the war’s small arms engagements are now beyond 500 meters, with the enemy employing heavier weapons and then withdrawing before air support or artillery fire can arrive". The reason for this seems to have been connected with the limited range of the 5.56 mm weapons being carried by most ISAF forces.


British foot patrols were initially equipped only with 5.56 guns; the L85A2 rifle, L86A2 Light Support Weapon, and L110A1 Minimi Para light machine gun. Similarly, US troops were primarily armed with the M4 Carbine (Army) or M16A4 rifle (USMC) plus the M249 LMG (Minimi). These all fire the standard NATO ball ammunition, designated SS109 (M855 in US service). However, this ammunition has proved inadequate at long range. Whatever performance they may demonstrate on a firing range, a combination of battle experience and the testing of ammunition terminal effectiveness has led to a judgment that weapons with the 500 mm (c.20 inch) barrels the ammunition was designed for  are effective only up to about 300 metres. Weapons with shorter barrels, such as the M4 and the Minimi Para, have reduced ballistics resulting in an even shorter effective range. What this means is that more than half the small-arms engagements take place beyond the effective range of the standard British infantry rifle, and about 70% of the engagements are beyond the effective range of short-barrelled carbines like the M4.

The second problem with 5.56 ammunition is its lack of suppressive effect, which is what most long-range small-arms fire is used for. On most occasions when British foot patrols  came under fire, they never saw their attackers; the Taliban are skilled at selecting concealed positions for ambush. So the soldiers returned fire in the general direction of the enemy in the hope of pinning them down long enough for heavier weapons to be brought to bear. Field testing has revealed that the suppressive effect of a small-arms bullet is directly proportional to the loudness of the sonic bang it generates, and in turn that is directly proportional to its size and of course to how close the bullets pass by. 5.56 bullets have only about half the suppressive radius of 7.62 fire, exacerbated by the fact that the little bullets are more affected by wind drift and therefore less likely to get close to the target at long range. This is supported by battlefield reports that the Taliban take little notice of 5.56 suppressive fire.

This lack of effective range and suppressive effect are the two major concerns with 5.56 ammunition which have been reported by the British Army, but there have also been complaints about two other issues which have long been highlighted in the USA and widely reported: erratic terminal effectiveness, even within its effective range, and poor barrier penetration. Erratic terminal effectiveness is mainly due to the fact that, while the M855 bullet is capable of inflicting incapacitating injuries at shorter ranges, it frequently does not yaw rapidly on impact but may instead pass through most of the body point-first. When this happens, it will inflict a relatively minor injury unless it hits a vital organ. There is anecdotal evidence aplenty of erratic effectiveness in combat (for example in an article in early 2011 in the Royal Marines' magazine, Globe and Laurel, which commented that it could take up to 15 hits to stop an attacker at close range), and this has been confirmed by laboratory testing, which reveals that 85% of the bullets do not start to yaw until they have penetrated at least 120 mm - which could take them most of the way through a body. While no small-arms cartridge is effective 100% of the time, the general consensus of those with combat experience with both 5.56 mm and 7.62 mm rifles seems to be that on average about twice as many 5.56 mm hits are required to cause rapid incapacitation. Problems with penetrating intermediate barriers such as walls or car doors and even windscreens have also been confirmed in laboratory testing. THIS 2008 presentation by Dr Roberts detailed these problems and illustrated the results of laboratory testing. The commander of the German troops in Afghanistan made similar complaints in 2009 about the poor effectiveness and barrier penetration of 5.56 mm ammunition. Interestingly, the British Army adopted a semi-automatic shotgun to provide more reliable close-range effectiveness than 5.56 weapons.

A 2009 analysis by Major Thomas P. Ehrhart, United States Army, of the performance of US Army small arms in Afghanistan makes similar points to the British studies concerning typical engagement ranges and the limited effective range of 5.56 mm weapons, and also stresses the importance of marksmanship training. In 2010 the US Army's Soldier Weapons Assessment Team carried out interviews with soldiers in theatre to discover any issues. The need for their carbines to be effective beyond 500 metres was one of the key requests from troops. The 7.62 M14 Enhanced Battle Rifle is proving so popular that the troops want it to be an organic part of squad equipment. And the 7.62 mm MK48 light machine gun is increasingly being carried instead of the 5.56 M249: as the Team put it; "lethality trumps weight reduction when extended ranges are required".

Not everyone agrees that 5.56mm weapons have such a short effective range. Some proponents argue that in good conditions they can be effective to 500 m in the hands of well-trained soldiers - although the ballistic graphs later in this article demonstrate that they will have a much harder job hitting targets, or getting close enough for suppressive effect, than with larger-calibre weapons. 

These shortcomings mean that British foot patrols started carrying 7.62 mm weapons in place of some of their 5.56 guns; the very effective L7A2 GPMG (similar to the US Army's M240) and the new L129A1 sharpshooter rifle, of which several hundred were purchased from 2010 as an Urgent Operational Requirement specifically to overcome the lack of range of 5.56 mm weapons. The problem with the GPMG is that both the gun and its ammunition are very heavy; most unwelcome given that reducing the burden of around 60 kg (132 lbs)  worn and borne by the infantryman in patrol order is one of the top equipment priorities of the British Army. The Army at one time planned to follow the US lead in adopting lighter 7.62 mm machine guns  - the 7.62 mm version of the FN MINIMI having been selected - to match the characteristics of the Russian PKM, although in the event these have only be acquired for special forces. Little can be done for now about the weight of the ammunition, however; a key issue with belt-fed machine guns.

US forces recently adopted new 5.56 mm ammunition with the aim of replacing the M855. In mid-2010 the US Army started to field the M855A1 EPR (Enhanced Performance Round, previously known as the LFS - Lead Free Slug), while the USMC selected in early 2010 the MK318 Mod 0 SOST (Special Operations Science & Technology). Both rounds are claimed to offer better performance from short-barrelled carbines, improved barrier penetration and more reliable terminal effectiveness. The M855A1 also penetrates more armour and contains no lead. Initial indications are that while the USMC is happy with the more consistent effectiveness of the MK318, the high-pressure M855A1 is causing some problems concerning barrel wear and gun life: the Individual Carbine competition held by the US Army in 2013 was abandoned when none of the competing guns was able to meet the Army's reliability requirements when using the M855A1 ammunition. Even if these new rounds do resolve the M855's penetration and effectiveness issues, their exterior ballistics are not good enough to eliminate the need for larger-calibre small arms to cover the longer ranges, and in any case they may not be acceptable to European nations, as we shall see.



That brings us up to date. 7.62 mm guns are being used much more widely, although their ammunition is big and heavy and generates nearly four times as much free recoil energy as 5.56 mm. Heavy recoil in a rifle makes it more difficult to train recruits, reduces accuracy, slows down rapid semi-automatic fire and makes fully automatic fire virtually uncontrollable. I have tried the 7.62 FN SCAR-H currently being acquired by the US Special Operations Command and recoil is sharp even in semi-auto fire: I was told by a soldier with extensive small-arms experience that only the first round of an automatic burst was likely to hit the target. But the 7.62 gets the job done, so do we really need a new cartridge? The 7.62 weapons can deal with the long-range work, with 5.56 carbines retained for short-range fighting.

One problem with this is that it may not be possible to draw neat lines around scenarios: a patrol may be clearing houses in a village at one moment then come under long-range fire as they leave. It means that those carrying 7.62 weapons will be less well equipped for the close-quarter battle, while those with 5.56 guns will be unable to participate effectively in long-range engagements or even to pass their ammunition over to those with 7.62 guns, thereby reducing the effective firepower of the section. Finally, it still leaves us with the 7.62's weight and recoil, plus the erratic terminal effectiveness and poor barrier penetration of the 5.56 M855.


Furthermore, the sudden proliferation of new small arms has increased the total number of portable rifles and MGs in the British section to five (not including sniper and special forces rifles): the three original 5.56 guns and two 7.62 ones: the L129A1 and L7A2. Even worse, the US Army and Marine Corps use eight between them: four in each calibre (M4, M16, M27 and M249 in 5.56; M14EBR, M110, M240 and MK48 in 7.62). This proliferation of weapons has obvious practical disadvantages in terms of procurement, training and maintenance. The evidence presented below suggests that it is possible to meet military requirements with a much smaller number of weapons. The key to this is the ammunition.


The performance of the ammunition determines the  potential of the weapon. So the design of future rifles or machine guns should start by defining the required terminal effects of a bullet against soft and hard targets out to a specified range (bearing in mind the likely growth in the use of body armour by potential opponents), and the exterior ballistics out to the maximum range for effective suppressive fire, in terms of the bullet's trajectory, susceptibility to wind drift and remaining velocity. Add in the expected barrel length and that provides most of the factors controlling the cartridge design. The gun should then be designed around the cartridge. That's the logical priority order anyway, although in practice it it doesn't usually happen that way - as demonstrated by the recent US Individual Carbine competition, which was theoretically open to calibres other than 5.56 mm, but in reality was not. Gun designers tend to be stuck with existing cartridges even though far greater improvements in capability could be achieved by changing the ammunition than by changing the guns.

Let us first consider what we want infantry rifles and light machine guns to achieve. I suggest the following:

First, their bullets should be capable of reliably inflicting sufficiently serious wounds to provide a high probability of an enemy being rapidly incapacitated by a centre-mass (torso) hit, within the effective range of the weapon and allowing for the current preference in many armies for short-barrelled carbines.

Secondly, their bullets should be capable of penetrating a wide range of intermediate barriers while still maintaining their trajectory afterwards; what's known as "barrier blind".

Thirdly, sharpshooter rifles and LMGs should have the effective range to at least match an enemy using full-power 7.62 weapons, since these are in widespread use and likely to remain so.

Finally, the weapons and their ammunition should have the lightest weight and lowest recoil consistent with the first three requirements.

These requirements are all essentially dependent on the right choice of ammunition. The first three can clearly be met by the 7.62 cartridge but this falls down badly on the fourth. The 5.56 round delivers the opposite results.


There are several possible approaches:

1. Retain the 5.56 and 7.62, but introduce an improved 5.56 loading.

2. Return to using the 7.62 in all weapons, preferably with an improved loading.

3. Replace the 5.56 with a more effective short to medium range cartridge, retaining the 7.62 in sharpshooter rifles and MGs.

4. Replace both existing rounds in the dismounted infantry section with one new general purpose cartridge (GPC) with good long-range performance.

The pros and cons of these options can be summarised as follows:

Option 1: Various attempts have been and continue to be made to upgrade the performance of the 5.56 mm cartridge; in US service we have seen the MK262 and now the MK318 Mod 0 and the M855A1, and these all offer some improvements in performance. These new rounds may mitigate to some degree the M855's penetration and effectiveness problems, but their exterior ballistics are not good enough to eliminate the need for larger-calibre small arms to cover the longer ranges. In any case, the degree of improvement is fundamentally limited by the small size and modest power of the cartridge. It's worth remembering that in many US states and in the UK, the 5.56 cartridge is considered insufficiently powerful to hunt anything other than small game, even when loaded with the more effective expanding bullets which are banned for military use.

Furthermore, the MK262 and MK318 have open-point bullets, which are regarded as unacceptable by the British and other European countries, for reasons which are worth a short digression. Declaration III of the 1899 Hague Convention, states that: "The Contracting Parties agree to abstain from the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions". US lawyers argue that the bullets are not designed to expand, so the clause does not apply; European lawyers point to the specific wording which prohibits jackets which do not entirely cover the core (leaving aside the fact that the base of nearly all military rifle bullets is not covered by the jacket anyway - the wording of Hague is rather sloppy). The M855A1 bullet also has a jacket which does not cover the steel tip, which is exposed. What's more, like the M855 the M855A1 appears to rely on bullet fragmentation to maximise its soft-target effectiveness (it fragments to lower impact velocities, i.e. at longer ranges) which is also regarded as unacceptable by UK lawyers because of the rather vague wording of the Geneva Conventions which prohibits the use of "weapons, projectiles and material and methods of war of a nature to cause superfluous injury or unnecessary suffering". The UK Manual of the Law of Armed Conflict (Ministry of Defence, 2004) states in its chapter on weapons: It is prohibited to use in international armed conflicts "bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core or is pierced with incisions. This prohibition is aimed at soft-nosed bullets that mushroom on impact or bullets whose casing is designed to fragment on impact causing, in either case, unnecessarily serious injuries". The original British L2A1 5.56mm ball bullet did fragment in a similar way to the M855, but this was made less likely in the L2A2 and subsequent patterns by using a thicker jacket. As a result of all this, the US rounds are very unlikely to be approved as NATO standards, although they may of course be adopted by individual NATO nations depending on the particular interpretation of international law which they accept. It also seems unlikely that the British lead-free 5.56 round currently being developed by BAE, which has a steel core, will offer the effectiveness improvements claimed for the M855A1 (it is intended only to match the effectiveness of the SS109/M855).

Option 2: The 7.62 M80 (the standard NATO ball round) is an old design which is effective but not very efficient. It is not efficient for two reasons. First, because the bullet does not usually yaw very rapidly on impact. Second, it has an unimpressive long-range performance for its calibre due to the poor aerodynamics of the bullet which sheds velocity quite quickly. It is effective simply through the size and power of the bullet which delivers considerable terminal effectiveness and barrier penetration, but that power has a serious cost in weight and recoil. Some improvements could be made by introducing a more modern and efficient loading, but apart from sniper loadings the only one to emerge so far - the new MK319 - also relies on an open-point bullet. The US Army plans to introduce in the near future an M80A1 using a lead-free bullet which is basically a scaled-up version of the M855A1, so that will also feature an unjacketed steel tip. These will also do little or nothing to mitigate the weight and recoil issues.

In the longer term there may be the possibility of using a combination of a significantly lighter but better-shaped lead-free bullet which matches the ballistics of the existing M80, in combination with a mostly polymer case. Such a case would not only reduce weight considerably, but could be moulded around the bullet, enabling the use of a more tapered, long-nosed shape in the interests of aerodynamics. Such a reduction in weight (and to a lesser extent recoil) would be very attractive and could be usable in existing weapons. However, such technologies have yet to be proved, and these weight saving methods could of course be applied to any calibre.

Option 3: To achieve a worthwhile performance increase over the 5.56 it is necessary to move to a larger calibre with increased case capacity. There will be some penalties in the form of increased weight and recoil, but these can be considerably less than the figures for the 7.62. The most thorough recent attempt emerged a few years ago as a joint effort between Remington and some soldiers within SOCOM; the 6.8 x 43 Remington Special Purpose Cartridge, or SPC. Muzzle energy and ammunition weight are half-way between the 5.56 and 7.62. Tests indicate that its terminal effectiveness and barrier penetration are very impressive, albeit achieved with an open-point bullet. In comparative shooting tests
(courtesy of Heckler & Koch) I found that the additional recoil appears to be quite modest, feeling much closer to the 5.56 than it does to the 7.62, despite the fact that the HK416/6.8 is lighter than the big HK417. However, the long-range performance, while better than the 5.56, is not good enough to replace the 7.62 as it is limited by the relatively short and light bullet needed to keep the overall length the same as the 5.56mm. The 6.8 mm Rem has achieved service status, being adopted for certain guard units first by Jordan and then (much more significantly in terms of numbers) by Saudia Arabia. However, the special loading developed for Saudi Arabia uses an even lighter bullet optimised for use in short-barrelled carbines and is only intended to be effective within about 300 m.

Another option for improving on the performance of the 5.56 mm are the almost identical .300 Whisper/Blackout rounds based on the 5.56 mm case, but in their supersonic loadings these do little more than replicate the ballistic performance of the Russian 7.62 x 39 M1943 cartridge in a smaller package.

Option 4: This option is based on the fact that once you are in the size and performance class of the 6.8 Remington, the right choice of calibre and - especially - bullet can in theory match the long-range performance of the 7.62 M80 with a much lower ammunition weight and recoil. This therefore opens the possibility of one common general-purpose cartridge (GPC) used by the weapons carried by the dismounted infantry section. While the extra range would initially benefit sharpshooters and LMGs and may not be needed in assault rifles, it does give them the potential for delivering long-range suppressing fire given the increasing use of telescopic sights and bipods, provided of course that appropriate training is given. Furthermore, advanced sights currently under development (incorporating laser rangefinders and ballistic computers) could enable all riflemen to fire more effectively at long range. If a single GPC could be achieved, the benefits resulting from all of the weapons within the squad/section being suited to use at all combat ranges and being able to share ammunition, plus the simplification of weapon and ammunition acquisition, logistics and training would, I suggest, make this the most attractive option. 


It is worth taking a brief look at what we can learn from cartridges developed in the past, before considering the specifications which could deliver Option 4.

One of the early small-calibre cartridges was the Japanese 6.5 mm Arisaka. When introduced in the late 19th century it had a round-nosed bullet but from 1905 the pointed-bullet Type 38 loading was introduced, and this remained in service until 1945. It was recognised to be an impressive performer, with terminal effectiveness comparable with the later 7.7 mm MG round. It developed a muzzle energy of 2,590 Joules (1,920 ft lbs), a figure worth remembering.

The US Army came close to adopting a reduced power, general-purpose cartridge eight decades ago. Following exhaustive testing by the Army's Caliber Board, the .30'06 round was very nearly replaced in the 1930s by the .276 Pedersen, which developed 2,390 J of muzzle energy. The British were very interested in this cartridge and even established an ammunition production line (the example in the photo below was made in England) but it was rejected by the US Army mainly on cost grounds, because of the large stocks of .30'06 ammunition.

The next attempt took place in the years following World War 2 during the trials to select NATO's first standard rifle and machine gun cartridge. As a result of WW2 experience there was a strong wish in both the US and British armies to adopt one general-purpose selective-fire rifle to replace the proliferation of weapons in service. The British wanted a rifle compact and controllable enough in automatic fire to replace sub-machine guns as well as the .303 rifle, the Americans wanted one which would replace their M1 Garand rifle, M2 Carbine, Browning Automatic Rifle and M3 sub-machine gun. For the NATO tests Britain submitted a new reduced-power 7mm round co-developed with Belgium and supported by Canada. Various designations were used as it developed, starting with the .276, then the .280, the .280/30 and finally the 7mm Mk 1Z, although it is now often referred to as the 7 x 43. This used a long, heavy bullet which lost velocity more slowly than the 7.62's, enabling it to deliver more energy at long range despite a lower muzzle energy (initially c.2,450 J)  with less weight and recoil. The British designed the EM-2 bullpup rifle around this cartridge in order to achieve the short gun needed for urban fighting combined with the long barrel needed for long-range fire. This combination was compact and controllable enough to replace sub-machine guns as well as the old .303 rifles. It was, for a time, officially adopted by the British Army. However, this had to be cancelled when the US Army insisted on their new .30 calibre cartridge which was duly adopted as the 7.62 NATO. Unfortunately, at 3,200-3,400 J this is just as powerful as the old full-power rifle/MG rounds which had seen service in both World Wars and, as we have seen, generates so much recoil that effective automatic rifle fire proved impossible. The M14 rifle in this calibre was therefore only able to replace one of the four weapons it was intended to: the M1 Garand rifle, over which it was only a modest improvement.

There have since been other attempts at a new cartridge, intermediate in power between the 5.56mm and the 7.62mm. The British developed an interesting 6.25mm cartridge around 1970, but this was not designed for very long range and used a relatively light bullet. A more promising approach is the 6.5 x 40, a recent private venture by Mitch Shoffner, which is basically a 6.8 mm Rem necked-down to the smaller calibre and shortened to allow the use of long, aerodynamic bullets while still being compatible with 5.56 mm actions. While this is not powerful enough to replace the 7.62 x 51, its long-range performance would probably be good enough to make the carrying of 7.62 mm weapons by dismounted troops normally unnecessary. Another recent private-venture experimental round is the 7 x 46 UIAC by Cris Murray, which is in effect a lengthened and necked-out 6.5 mm Grendel. Thishas plenty of performance, but may be too close to the 7.62 mm to stand much chance of adoption.

The other two shown in the slide above are particularly relevant because they achieved a good long-range performance from a small cartridge by using a heavy bullet at a medium velocity. One was a US Army project from around 1970; the 6 x 45, for use in a squad automatic weapon. This was intended to provide superior long-range performance to the 5.56 but was abandoned when improved 5.56 ammunition was promised. Well, this eventually arrived as the M855. The most recent production round to deliver high energy to long range by firing a heavy, reduced calibre bullet at a moderate muzzle velocity is the 6.5mm Grendel from Alexander Arms (6.5 x 38).

Let's look at how the two most recent intermediate-power cartridges perform compared with the service rounds. This chart of bullet energy at different ranges compares the 7.62 with the 5.56, the 6.8 Remington and the 6.5 Grendel. Both the Remington and the Grendel rounds can develop up to 2,500 J muzzle energy - very similar to the 6.5mm Arisaka, the .276 Pedersen and the 7 x 43.

Two things are obvious: first, that the initial performance gaps between the 5.56 and the 6.8, and between the 6.8 and the 7.62, become steadily wider with increasing range. The second point is that the 6.5 performs differently; while starting with a muzzle energy similar to the 6.8, its longer, thinner and more aerodynamic bullet allows it to match the 7.62 at long range. It also offers a flatter trajectory and much less wind drift despite its lower muzzle velocity, as demonstrated in the graphs below. The four rounds are shown together here with their bullets. Note that the design of both the 6.8 and the 6.5 was constrained by having to fit within a converted AR-15, so the total length had to be the same as the 5.56. This prevents the 6.8 from using long bullets with good long-range performance. With a new calibre and family of weapons, this need not be a constraint.


One important reservation concerning the impressive performance of the Grendel is that these results were obtained with the use of a low-drag, lead-cored target bullet. The US Army has since chosen to develop lead-free small-arms bullets to minimise the risk of environmental pollution on practice ranges; the M855A1 EPR is the first, but a 7.62mm equivalent is planned to enter service in 2014/15. Other nations generally accept, however reluctantly, that they will eventually have to follow suit as far as ball ammunition is concerned, although lead-cored bullets may well be retained for special purposes like sniping, for which ammunition expenditure is extremely low. Therefore a GPC must be able to deliver results with lead-free bullets; but it is very difficult to match the performance of a lead-cored target bullet with a mass-produced lead-free military ball round, as we shall see, and this indicates that the Grendel may be just too small to do the job required.

There are three alternative metals to lead commonly found in bullet cores: steel, copper and tungsten. Of these, tungsten is the only one which is more dense than lead (170% of the density) but is reserved for armour-piercing ammunition because of its high cost (20 times as much as lead). In any case, all heavy metals tend to be toxic to some degree, so there would be little environmental improvement from using it. So in effect mass-produced lead-free bullets are limited to copper (or copper alloy, such as brass) and steel. Copper has 80% of the density of lead but is about four times the price; steel has 70% of the density but is only a quarter of the price (although specially hardened alloys to improve penetration will be costlier). Machine-turned solid brass bullets are often used in very low drag designs for long-range target shooting as they can be made with great precision, but they are costly in materials and manufacturing and do not penetrate armour as well as hardened steel. So for the EPR, the US Army selected a large hardened-steel penetrator in the nose backed up by a copper slug, the two held together with a copper-alloy semi-jacket. This is replacing the M855, which has a smaller steel penetrator in the tip of an otherwise conventional lead core, with a jacket covering the lot. The standard NATO 7.62mm ball round, the M80, just has a jacketed lead core.

The lower density of copper and steel means that to achieve a given weight, they need to be longer than bullets with lead (or mostly lead) cores of the same calibre. Assuming that a bullet is 50/50 copper/steel by volume, then its overall density and therefore mass will be only about 75% of that of a bullet of the same size and shape with a plain lead core (it isn't quite as simple of that, because lead-cored bullets have jackets of a different material - copper alloy or steel - but I'll ignore that to avoid undue complication). This means that to bring the mass up to the same as the lead-cored version the bullet must increase in volume by something like 30%; which in any given calibre, means it must increase in length by about that much. This potentially causes two problems: packaging the ammunition, and stabilising the bullet.

For an existing cartridge, in which there is usually no room to have the bullet protruding further from the case without exceeding the limits on overall cartridge length (above which the ammunition may not fit into the gun actions or magazines), it is necessary for the lead-free bullet to extend more deeply into the case, reducing the space for propellant. Unless a more volume-efficient propellant with the right pressure characteristics can be found, this means that the muzzle velocity and energy achieved at any given chamber pressure will be reduced.

Bullet stabilisation depends on the relationship between its length/diameter ratio (L/D) and the barrel rifling twist. In any given calibre, the longer the bullet, the tighter the rifling twist needs to be. In practice, there is a limit in the L/D of about 6:1, beyond which stabilisation by rifling is no longer feasible (e.g. a calibre 6 mm bullet cannot exceed 36 mm in length; in fact, standard military bullets typically have L/Ds of around 4:1). Which is why long, thin, discarding-sabot projectiles are stabilised by fins at the end and are preferably fired from smooth-bored guns. Of the bullets shown above, the performance champion is the 6.5mm Grendel's 123 grain (8 gram) Lapua Scenar, which has a purely lead core.  It is good because of its long thin shape, but this means it already has an L/D of about 4.5:1. Adding 30% to its 30 mm length would bring this up to about 39 mm, with an L/D of 5.8:1 - extremely close to the absolute limit and requiring the tightest possible rifling twist. Bearing in mind that any military machine gun ammunition must include tracer bullets and these are almost invariably longer than the ball bullets (as their chemical contents are much less dense than core metals), this is simply too long. The extra 9 mm of length would also have to be packaged somehow.  In practice, around 7 grams (108 grains) is probably around the maximum feasible in 6.5 mm calibre for a copper+steel EPR bullet. This will be about 34 mm long, giving an L/D ratio of about 5:1. Just about acceptable, although probably too long for the Grendel, which is why I said it is just too small for a GPC. It also means that the lighter EPR-type bullet will not match the ballistic performance of the 8 gram lead-cored bullet, as I will illustrate later.

Incidentally, the smaller the calibre, the harder it becomes to achieve a low-drag bullet in lead-free materials. The best ballistic performer of the 5.56 mm loadings to have seen military service, the MK262, uses a lead-cored target bullet weighing 77 grains (5 grams). This is 25 mm long, giving an L/D ratio of 4.4:1. An EPR bullet of the same weight would be around 32.5 mm long, giving an L/D of 5.7:1 - too long, once tracer bullets are added. Yet the MK262, although a very good performer by 5.56mm standards, doesn't even match the 7.62 mm M80 in its ballistic performance (it has a slightly worse G7 ballistic coefficient of .190 - see below)  and, as we have seen, the M80 is a very mediocre performer compared with the Grendel.


Taking all of these issues into account, it is possible to draw up the characteristics of cartridges to meet the requirements. The calibre could be anywhere between 6 mm and 7 mm, although at the smaller end of the scale designers may struggle to provide a worthwhile improvement over the 5.56 mm (especially with lead-free bullets), while at the larger end the problem will be a weight and recoil which may be too close to the 7.62 mm to be worth the cost of changing.  Some useful pointers emerged from some practical tests carried out by the US Army's ARDEC (Armament Research, Development and Engineering Center) Small Caliber Munitions Technology Branch to determine the optimum calibre for a military rifle, with the results emerging in March 2011. A wide range of criteria were examined including: penetration; terminal effectiveness; accuracy; initial, retained and striking energy; wind drift; stowed kills; and recoil. 5.56 mm and 7.62 mm rounds were compared with 6 mm, 6.35 mm and 6.8 mm, all loaded with lead-free copper+steel bullets to represent the EPR. The overall outcome of the study was that both 6.35 mm and 6.8 mm comprehensively outperformed the others in their overall balance of characteristics. In 2012 AMU - the US Army Marksmanship Unit - carried out another study by into the optimum cartridge for a future infantry carbine, and that this concluded that the cartridge length and diameter should be greater than 5.56 x 45, the calibre should be 6.5 mm and the muzzle energy around 2,500 J, with low-drag bullets (G7 BC =.250+; see below) being used to provide good long-range performance, bettering that of the 7.62 mm M80.

These conclusions are supported by a growing view that the next US rifle should be effective at ranges of up to at least 600 m and that 5.56 mm could not deliver this, no matter what bullets were loaded. The outcome of these studies should hardly be a surprise, since as Major Ehrhart observed in his study mentioned above: "The 2006 study by the Joint Service Wound Ballistics – Integrated Product Team discovered that the ideal caliber seems to be between 6.5 and 7-mm. This was also the general conclusion of all military ballistics studies since the end of World War I."

ARDEC did not study the 6.5 mm calibre, but as this is bracketed by their two preferred calibres as well as being the apparent preference of AMU, it seems reasonable to select 6.5 mm in order to work up some examples of how a purpose-designed GPC might perform. The examples which follow are therefore merely to illustrate the potential; the optimum characteristics including the calibre would only be determined after extensive practical testing of various options.

The impressive ballistic performance of the Grendel gives some clear goals at which to aim for our concept demonstration cartridges. This indicates that the muzzle energy, weight and calculated recoil of the GPC should be approximately midway between the 5.56 and 7.62 - similar to the 6.8 Remington and 6.5 Grendel. The bullet's performance at 1,000 metres should be comparable with the 7.62 M80 ball, as measured by hit probability (a function of trajectory, flight time and susceptibility to wind drift) and damage potential (bullet energy and penetration). In order to achieve this the GPC needs to use a low-drag bullet (more technically, one with a high ballistic coefficient, or BC) to minimise the velocity loss with range. This is important because a low-drag bullet brings substantial benefits. As it loses velocity more slowly, achieving a given performance at maximum range means that it can start off at a lower velocity than a higher-drag bullet; which means that less propellant will be needed, the cartridge can be smaller and lighter and will generate less recoil. The current 7.62 NATO bullet has a very mediocre ballistic coefficient, or BC; the 5.56 is worse still.

I should note at this point that there are two different methods of calculating the BC of rifle bullets: the standard commercial one is designated G1, and applies to pointed bullets with flat bases; the more appropriate one for low-drag boat-tailed bullets (i.e. tapering towards the base, as with all the examples shown here) is designated G7. The difference matters, because G1 figures come out at around twice as high as G7 (which is probably why commercial manufacturers like using them - they look better!). All of the BCs quoted here are G7.

There are two factors which determine the BC of a bullet in any given calibre: the mass (heavier is better) and the shape, or form factor (FF). The problem with adding mass is that it increases both ammunition weight and recoil; so the FF needs to be as good as possible. That means the bullet needs a long, gently tapering nose. Are there any current military rifle/MG bullets with a good FF which can be taken as a model? Yes, there is one - the standard Russian 5.45 mm ball bullet as used in the ammunition for the AK-74 assault rifle and RPK-74 squad automatic weapon.


The slide above shows the standard Russian 5.45mm ball bullet in comparison with the NATO 5.56 and 7.62, with their form factors and ballistic coefficients as measured by the US Army's Ballistic Research Laboratory. These figures show that the FF of the 5.45 is better than that of the other two bullets (a lower FF is better, in contrast with the BC in the final column in which a higher figure is better). I have included in the yellow box figures for a couple of theoretical 6.5mm bullets, an 8 gram lead-cored one and a 7 gram one which, as discussed above, is probably around the maximum feasible length for a lead-free bullet in this calibre. Simply matching the 5.45's FF in such bullets would provide the potential for a good long-range performance, even in a lead-free version, as you can see by the BCs in the bottom right of the chart. These bullets would lose velocity more slowly than the 7.62 ball, let alone the 5.56. Incidentally, the 5.45 mm is not the first to have such a good FF: the German 7.9 mm heavy ball, made by the billion in WW2, had an FF in the .900s.

The slide above involves a bit of photoshopping to illustrate these issues. The first two pairs of cartridges show the current 5.56 and 7.62 next to what they would look like with scaled-up 5.45 bullets. As can be seen, these cartridges cannot accommodate such finely-tapered low-drag bullets because that would make them too long to fit into rifle magazines and gun actions. They are therefore fundamentally restricted in the ballistic improvements which are possible. The last two photo mock-ups show two different 6.5mm cartridges with similar bullets (these are not meant to represent the ideal, they are just to illustrate what might be possible). The cases have different lengths and diameters but are both approximately the right size to provide a muzzle energy of around 2,500J, midway between the 5.56 and 7.62. The first one is based on the 6.8 mm Rem case (10.7 mm diameter) slightly lengthened and, more important, with a much longer overall length to allow the low-drag bullet to be used. The second is based on the Grendel (11.3 mm diameter), only lengthened by a few mm to provide a greater case capacity and of course also with a greater overall length. How might these perform?

The next few charts, compiled using the JBM ballistic calculator, compare the performance of the 5.56 mm and 7.62 mm NATO rounds with these two 6.5 mm cartridges. 20 inch (508mm) barrels are assumed in all cases for comparison purposes (armies may choose shorter barrels for their rifles, but the resulting reduction in performance is likely to apply more or less equally to all calibres). The first one (above) shows the velocities with range; the 8 gram 6.5 mm bullet starts off the slowest but overtakes the 7.62 by 200 metres, while the 7 gram bullet remains faster throughout its flight; the 5.56 starts the fastest but after 400 m becomes the slowest.

The second chart shows the energies with range; the heavy 6.5 catches up with the 7.62 by 500 metres, the light one by about 700 metres; the 5.56mm is outclassed at every range, and drops ever further behind as the distance increases.

The third chart shows the bullet drop in centimetres from rifles zeroed at 100 metres; at 1000 metres both 6.5s will have dropped about 12.5 metres below the line of sight, the 7.62 more than 15 metres, the 5.56 nearly 17.

The fourth shows the wind drift in a 10 mph cross-wind, an important element in long-range hit probability; at 1000 metres the heavy 6.5 will be blown sideways about 3 metres, the light lead-free 6.5 about 3.3 metres, the 7.62 about 4.25 m and the 5.56 about 5.4 m. Even at shorter ranges, this can make the difference between solidly hitting a target and entirely missing.

The fifth chart shows the time of flight of the bullet in seconds; both 6.5 bullets take about 1.9 seconds to reach 1000 metres, the 7.62 about 2.1 seconds and the 5.56 about 2.2.

The sixth slide shows the potential for armour penetration (assuming similar AP bullet designs); this is calculated by dividing the energy by the cross-sectional area of the bullets. The numbers on the chart represent joules per mm˛. There isn't much difference at close range, but the gaps widen as the range increases, the 6.5s gaining a clear advantage while the 5.56 suffers particularly badly.

Barrier penetration is calculated differently from armour penetration as it requires momentum rather than energy to plough through thicknesses of material. This chart is the result of multiplying the bullet weight by the muzzle velocity and then dividing the result by the cross-sectional area of the bullet. The numbers on the chart represent grams x metres/sec divided by mm˛. Again, it's the 6.5s (especially the heavy lead-cored one) which lead the way with the 5.56 trailing badly.

The 6.5s have two other advantages over 7.62 as shown here: their weights achieve an estimated reduction of around 25% (particularly useful in belt-fed MGs), and the free recoil energy in equivalent guns is reduced by 40-50% (important in rifles). Not surprisingly, these are the only areas where the 5.56 has a clear advantage over the other rounds, but since its poor performance at long range means that it is incapable of fulfilling the role of a GPC, that is rather academic.

To sum up, the 6.5s don't just match the 7.62's long-range performance; they are clearly superior to it despite their much lower muzzle energy, even when suffering the performance penalty of a lead-free bullet. And that's by using a bullet of a shape which the Russians have been churning out by the million for four decades, so no unrealistic assumptions have been made. Needless to say the 5.56 trails badly in most of these comparisons and becomes completely outclassed at longer ranges. Something like the lead-free 6.5 shown above would provide a substantial weight saving over 7.62 without losing anything in long-range ballistics or penetration at any range. Combined with a recoil midway between 7.62 and 5.56, this would make it a viable candidate for a GPC.


The preferred US Army EPR design features an exposed steel penetrator, and it seems likely that the same design would be adopted in any other standard rifle/MG calibre. However, to satisfy European requirements, the standard (ball) bullet must be compliant with their interpretation of the Hague and Geneva Conventions. Which is to say that in a jacketed bullet, the jacket must fully enclose the nose and sides of the bullet. Furthermore, the bullet must not only not expand on impact, it should be designed so that it does not readily fragment either. It is possible for a non-jacketed bullet to meet these requirements; the solid brass target bullets already mentioned will neither expand nor fragment (amazingly, one of the early "small calibre" military bullets, the French 8 mm Balle D of 1898, was made from solid brass, and was the first to have a finely-pointed nose, and was the first to have a boat-tail to minimise drag at long range; it is an impressive performer even today).  Both RUAG and Nammo offer steel-cored fully-jacketed lead-free loadings in military calibres now, so such designs could easily be applied to a GPC. Another possibility is the RUAG 7.62 mm HC type, which is basically a steel bullet with the sides and rear enclosed by a brass "shoe" to take the rifling: however, it may be more difficult to get this to work with a 6.5 mm high-BC bullet, because of the L/D problem described earlier. In any case, armour-piercing and tracer rounds also need to be developed at the same time (although with any steel-cored types, providing AP performance may be merely a matter of using harder steel).

One aspect of bullet performance which is difficult to quantify is the terminal effectiveness against unprotected human targets. As we have seen, with non-fragmenting, non-expanding bullets this depends on the rapidity and reliability with which the bullet yaws after impact. Rapid yaw means that the bullet is more likely to stop within the target (or at least exit at low velocity) and therefore less likely to result in collateral damage by continuing on to strike someone else. The problem is that this aspect of performance can be significantly affected by quite minor changes in bullet shape or construction so is difficult to predict with any confidence: a great deal of experimental work would be required to maximise the probability that the bullet does not over-penetrate in human targets.

As already mentioned, the bullet also needs (as far as is feasible) to be "barrier blind" - maintaining its trajectory after passing through intermediate barriers, such as windscreen glass, on the way to the target. This again is difficult to predict in advance.

All in all, the design of a bullet to meet these varied requirements (some of which may be in conflict with each other) will be a complex exercise in juggling priorities and will involve a lot of trial and error in the development programme, but it is important to the success of the GPC concept to get it right: the bullet is the key!  

You may have noticed that I have said little so far about advanced ammunition concepts; cases of stainless steel, light-alloy or polymer or entirely caseless, and perhaps of telescoped design. That is because I am primarily concerned with the performance of the bullet after it has left the gun; how it gets to that point is a secondary issue. I will merely comment that if an entirely new gun and ammunition system such as LSAT, using plastic-cased telescoped cartridges of cylindrical form, were to be adopted, it would in my opinion be a terrible waste of an opportunity if this merely replicated a calibre we already have, simply because we already have it. An LSAT GPC would weigh no more than the current 5.56mm, which would of course make the GPC concept even more attractive: the arguments for LSAT and for a GPC are mutually supportive. Even if LSAT leads to nothing, current developments in lightweight conventional cases (especially part-polymer) as briefly described under Option 2 above, promise weight savings of 25-30% over brass-cased ammunition, which will apply whatever their calibre.


Finally, I would like to address a few of the objections to the proposed general purpose cartridge, because I've heard a lot of them!

1. "The problem is not the ammunition, it's the training: just train soldiers to shoot straight." Of course, training is by far the most important element in soldier performance, and given the current emphasis on infantry small-arms the development and maintenance of rifle-shooting skills should be a high priority for all infantry, not just for a few marksmen. However, it is unrealistic to expect soldiers in combat to hit a small strip a few inches wide running from the forehead to the upper chest, as I have seen suggested as a solution to the 5.56's effectiveness problem. In any case, we go to a lot of trouble and expense to make sure that our troops are well trained and equipped; why shouldn't they also have the most effective weapons we can provide? At the very least, it can't hurt morale to have weapons which the soldier is confident can do what's needed over any likely engagement ranges.

2. "The 5.56mm performs well at long range; troops can hit targets out to 500-700 metres." The 5.56mm can hit targets at long range in ideal circumstances and with skilled shooters: but it is far more subject to drift in cross-winds than a GPC would be; the smaller sonic bang as it goes past has less of a suppressive effect (and the bullet becomes subsonic earlier anyway); and it has far less energy to do work when it gets there. It is significant that as soon as Taliban attacks started to be launched from long range, ISAF troops were willing to carry 7.62 mm rifles and machine guns, despite their extra weight. The 5.56 mm was thought to be perfectly satisfactory in peacetime, but the test of combat proved otherwise.

3. "Ammunition with very long range capability is wasted in a rifle anyway, because only snipers and marksmen are trained to shoot that far." For now, the long-range capability would primarily be of benefit in LMGs and sharpshooter rifles, although it would also aid ordinary riflemen in delivering effective suppressive fire - the main purpose of  long-range small-arms fire - for which a lesser standard of accuracy is required than that for scoring hits. However, advanced sights currently in development include laser rangefinders and ballistic computers and can also take into account crosswinds and other variables. Although initially intended for snipers, it is not difficult to predict that they will become small and inexpensive enough to be available for infantry rifles within the foreseeable future. These will do for long-range rifle shooting what precision guidance kits have done for aircraft bombs, and will enable an average soldier to deliver accurate rifle fire to long range - provided that the ammunition is effective at such a range.

4. "The extra weight of an intermediate cartridge over the 5.56 would increase the soldier's burden." With ammunition weight midway between 5.56 mm and 7.62 mm, the overall weight burden for a given number of rounds will depend on the mix of weapons in the squad; if more 7.62 mm than 5.56 mm ammunition is currently carried, then there will be an overall weight saving with the GPC.  In any case, when engagements take place beyond the effective range of 5.56 mm weapons (as they have done about half the time in Afghanistan) the 5.56 mm weapons and ammunition become useless dead weight, whereas GPC and 7.62 mm weapons will be effective at any range. Furthermore, advanced ammunition developments such as part-polymer cases or the LSAT programme have the potential to keep the GPC weight down to levels comparable with the current 5.56 mm.

5. "Soldiers within a section don't exchange ammunition between rifles and belt-fed machine guns anyway, so ammunition sharing isn't realistic". That misses the point: a British 8-man infantry section normally includes one 7.62 mm belt-fed MG, one 5.56 mm belt-fed MG, one 7.62 mm rifle, and 5.56 mm rifles. The US Army has a similar mix. So the machine-gunners can't share MG belts, and the riflemen can't share magazines across the calibres. That adds a significant element of tactical inflexibility. This is even more significant if the LMG is magazine-fed, as it is in some forces, since a GPC will allow magazines to be exchanged between all members of a squad.

6. "Fiddling with the calibres isn't worth the effort; there is no such thing as a 'golden bullet' that will put the enemy down first shot every time." This is true, but it's a question of probability: how often will the cartridge fail to do the job? Both combat experience and lab testing indicate that, other things being equal, the smaller and less powerful the cartridge, the more likely it is to fail to incapacitate the target rapidly.

7. "The GPC concept is untried: it's just an internet fantasy". Every concept is untried until it's actually made and tested. However, the calculations are firmly based in reality, not fantasy. The bullet FF is the same as the Russian standard military bullet; the cartridge sizes and muzzle energies are closely based on existing production rounds; the ballistic calculations are standard and reliable. There is no reason to doubt that it will perform as it should. What is uncertain is the terminal effectiveness, but that is true of any new bullet.

8. "A GPC would be such a compromise that it would be bad at everything". The ballistic calculations are based in reality (see above) and show that the GPC can match or beat the 7.62 mm in virtually every performance criterion, with the exception of terminal effectiveness which is unknown (but we do know that the 7.62 mm M80 is not a stellar performer for its calibre, since it yaws only slowly on impact). The GPC's ballistics would be superior to the 5.56's in every respect (again, the terminal performance would need to be tested).

9. "A GPC would just add one more calibre: the 5.56 mm and 7.62 mm will remain in service." The focus of this concept is on the needs of dismounted infantry who have to carry their weapons by hand. For them, the GPC would mean carrying one type of ammunition, one type of rifle, and one type of machine gun, rather than two of each, so keeping them supplied would be simpler. There would be no urgency about replacing vehicle-mounted 7.62 mm MGs, although the GPC could be expected to take over eventually. Similarly, 5.56 mm (especially in lightweight carbines) could be expected to remain in service with non-infantry troops as personal defence weapons for an indefinite period - although the cartridge is not optimal in short-barrelled guns, so ultimately a better solution may be found.

10. "The GPC bullet requires such a high BC that it would never work in practice." Not true. The BC is a function of the calibre, the weight and the form factor. The assumed FF is the same as the mass-produced Russian 5.45 mm, so we know it can be done.

11. "Why choose 6.5 mm calibre with a muzzle energy at 2,500 Joules?" That is chosen for illustrative purposes only. The end result of a lot of evaluation might well have a smaller or larger calibre, and be more or less powerful. I think that 6.5 mm and 2,500 J represent the approximate mid-point of the likely range of values, however, as indicated by number of previous intermediate cartridges around this figure: the optimum calibre of around 6.35-6.8 mm was also identified in the US Army's ARDEC trials of 2010/11, and both the calibre and muzzle energy are supported by the 2012 AMU study.

12. "Why not settle on one specification for the GPC, instead of leaving it open?" Because there is uncertainty over the outcome of the extensive comparative trials which would be needed before the final configuration could be decided: and the NATO armies (especially the US Army) would have to lot to say about the final outcome.

13. "The historical trend for well over a century is for ammunition to become steadily smaller: anything new would probably be smaller than the 5.56 mm". Considering that the 5.56 mm was adopted mostly by accident (it was pushed on the US Army as a short-term expedient which they did not want) and that there has been a vocal body of opinion ever since that while something smaller than the 7.62 mm NATO was needed the 5.56 mm was a step too far, that seems unlikely. The fundamentals of exterior ballistics remain the same, regardless of technical developments.

14. "Small arms don't matter at long range - immediate heavy fire support will always be on call." This may not necessarily be the case in counter-insurgency scenarios when foot patrols may be thinly spread over a wide area. And even when it is, the risk of collateral damage may restrict its use: US artillery and air support has been considerably restricted in Afghanistan for this reason. As General Petraeus said: "Every Afghan civilian death diminishes our cause." Use of excessive force, he argued, could turn "tactical victories" into "strategic setbacks".

15. "The calibre of the small arms will have no effect on the outcome of a war." The same could be said about most other military equipment, and it isn't really the point: the effectiveness of their small arms makes a great deal of difference to the soldiers whose lives may depend upon them.

16. "It would cost too much to change calibres, there are other priorities for our limited funds." Clearly we have budgetary problems and I am not suggesting any immediate change - developing new ammunition and weapons will take years anyway. However, the guns are wearing out and a new generation of small arms needs to be introduced in due course, providing an opportunity to phase in a new calibre. This would especially be true if LSAT were to be adopted. And adopting one general-purpose cartridge would halve the number of different weapons required, saving money in the long run on acquisition, training and support.

17. "Afghanistan is not typical in its emphasis on long-range fire; if we changed calibres we would be equipping for the last war, not the next one." Current thinking in both the British and US Armies is that counter-insurgency warfare will remain the most probable type of conflict. That means the infantry and their weapons will remain key elements. If you look at the less stable parts of the world, such conflicts are just as likely as not to take place in areas where there are opportunities for long-range fire. It is worth emphasising that full-power 7.62 mm rifles and machine guns are still in common use around the world, and facing an enemy armed with these puts troops equipped with 5.56 mm weapons at a disadvantage, increasingly so as the range lengthens. It is unlikely to be an accident that Taliban attacks are so frequently launched at long range - they will know the limitations of the 5.56. Besides, what would be the downside of adopting an intermediate calibre even if future combat is at shorter ranges? We would still benefit from ammunition that is designed to be much more effective than 5.56 at any range while being lighter and more controllable than 7.62. Would that be so bad?

18. "We would never get all of the NATO nations to agree to change to a new intermediate cartridge." We don't have to. The US Army unilaterally adopted the 5.56 mm round about fifteen years before NATO (and even then, some NATO nations didn't switch to the 5.56 mm for a long time). For pistols and SMGs the 9x19 is the only NATO-standardised cartridge, which hasn't stopped Germany and Norway from adopting the 4.6 mm or Belgium the 5.7 mm. Even the fervently law-abiding UK has adopted the .338 LM for sniper rifles - which is not NATO standardised. And does anyone seriously imagine that if the US decides to go for LSAT they would wait until all of NATO agreed before making the move? Realistically, it would be problematic for any single country to adopt a new standard rifle/MG cartridge without the USA being on board; but if they are, what the rest of NATO decides doesn't really matter.


In 2011 a report emerged from the
US Army's Program Executive Office Soldier: Soldier Battlefield Effectiveness. This analysis covers a lot of ground and is well worth reading, but I have selected just a few quotes concerning the ideal characteristics of infantry rifles and their ammunition:

"A Soldier must be able to engage the threat he’s faced with – whether it’s at eight meters or 800."

"To be effective in all scenarios, a Soldier needs to have true “general purpose” rounds in his weapon magazine that are accurate and effective against a wide range of targets."

"Weapons….must be accurate and capable of engaging the enemy at overmatch distances."

In 2013 the US Army announced a 'Caliber Configuration Study' to support two new small-arms programmes, designated CLAWS (Combat Lightweight Automatic Weapon System) and LDAM (Lightweight Dismounted Automatic Machinegun). The announcement was made at an NDIA (National Defense Industries Association) conference held in mid-November at the Army's Picatinny Arsenal.

CLAWS is intended to result in the eventual replacement of all of the existing 5.56 mm rifles, carbines and light machine guns by one modular weapon family with interchangeable barrels, stocks and accessories. This is expected to consist of a carbine (barrel length c.300 mm), assault rifle (c.400 mm), squad designated marksman rifle (c.500 mm), and a squad automatic weapon / light machine gun (c.600 mm barrel).

LDAM is seen as an eventual replacement for the 7.62 mm M240 medium machine gun (FN MAG) and the .50 calibre (12.7 mm) heavy machine gun in dismounted applications.

The calibres of the new weapons have yet to be determined, but the requirements indicate the replacement of the existing 5.56 mm and 7.62 mm NATO rounds that have been in US service for 50 and almost 60 years respectively. LDAM is intended to match the effective range of the .50 Browning with much less weight, so it needs to fire a considerably larger and more powerful cartridge than the 7.62 mm. The obvious existing candidates are the .338 inch (8.6 mm) Norma and Lapua Magnum rounds which differ only slightly, with weapons designed for one being readily adaptable to the other. The Lapua round is in widespread use in long-range sniper rifles (including the British Army's L115 from Accuracy International), while the Norma cartridge was selected for the General Dynamics LWMMG (Lightweight Medium Machine Gun) revealed in 2012. This weighs little more than the M240, although the ammunition is significantly heavier.

If the supporting fire role is to be filled by weapons in 8.6 mm or similar calibre intermediate in power between the 7.62 mm and 12.7 mm, that implies that the CLAWS weapons will need to replace some of the lighter current 7.62 mm rifles like the M14EBR and M110 (the British equivalent being the L129A1 'Sharpshooter'), plus light machine guns such as the MK48 (FN 7.62 mm Minimi). A reduction in effective range will probably be unacceptable, which means that whatever cartridge is chosen for CLAWS will need a longer range than 5.56 mm can provide - in other words, it would need a specification similar to that of the GPC discussed above.


1. The limited, counter-insurgency type of warfare seen in Afghanistan is likely to recur in future conflicts. Such conflicts put the emphasis on dismounted infantry operations, because of the need to provide a reassuring presence to the population. The need to minimise the risk of civilian casualties or other unintended damage also puts the emphasis on high-precision weapons of limited destructiveness, particularly small arms.

2. Small arms engagements may take place anywhere between 0 and 800+ metres. The US Army's PEO Soldier report identifies the need for general purpose rifles and ammunition effective at all ranges.

3. 5.56 mm ammunition has limited range, and effectiveness problems even at short range when using NATO-standard ammunition; 7.62 mm ammunition suffers from weight and recoil issues. Neither is capable of significant improvement which would adequately address these problems.

4. It is now technically feasible to develop a combination of weapon, ammunition and sights which is effective across the entire 0-800+ m range. The enhanced firepower and flexibility this would offer over a mixed-calibre infantry section, plus the savings in procurement, logistics and training, make this a desirable aim for the next generation of small arms.

5. Recent work by the US Army's ARDEC and AMU has separately identified similar characteristics for the optimum cartridge for future military rifles: around 6.5 mm calibre, and around 2,500 J muzzle energy.

6. The aims of the CLAWS element of the US Army's Caliber Configuration Study indicate that a calibre between the 5.56 mm and 7.62 mm might be favourably considered for future portable small arms.

7. Work should therefore be undertaken by NATO nations to determine the optimum specification of a general-purpose small-arms cartridge and to develop ammunition, weapons and sights accordingly.

A follow-up article looking at the characteristics of the next generation of military small arms is HERE

A history of the development of assault rifles and their ammunition is HERE


godaddy hit counter