The project to replace the current M4 Carbine, the Army’s standard infantry rifle, started in 2011 with a request for proposals from small-arms manufacturers. An analysis of the proposals resulted in a shortlist of six, with designs from Fabrique Nationale of Belgium, Heckler & Koch of Germany, Beretta of Italy and three US companies: Colt, Adcor Defense, and a joint effort by Remington, Magpul and Bushmaster. The competition reached Phase II – testing the shortlisted carbines – with a decision expected by the end of 2013.
However, earlier this year the competition was criticized by the Defense Department, resulting in the Army announcing in May the suspension of the tests amid rumors of imminent cancellation. To forestall this, the House of Representatives Armed Services Committee voted in June in favor of an amendment to the 2014 National Defense Authorization Act which would require the Army to complete the competition. Only a few days later the situation changed again, with the Army announcing that “the Individual Carbine (IC) competition will formally conclude without the selection of a winner. None of the carbines evaluated during the testing phase of the competition met the minimum scoring requirement needed to continue to the next phase of the evaluation.” It appears that the high-pressure M855A1 EPR ammunition used in the tests caused problems with achieving the reliability target.
In parallel with the competition, the Army has been running an improvement program for an M4A1 Carbine, involving the replacement of the 3-round burst with automatic fire and the provision of a heavier barrel (with further improvements planned), and orders for the this improved version have already begun to be placed. The winner of the carbine competition was supposed to be tested against the improved M4A1 to determine which should be purchased in the future. The Army now plans to continue acquiring the M4A1.
At the same time, there has been an apparent cooling of interest in the Army’s Lightweight Small Arms Technologies (LSAT) program, involving the development of advanced caseless and plastic-cased telescoped 5.56mm ammunition and associated machine guns and carbines. The weight savings achieved with the prototypes have been in the order of 40%, but the recent statements by the Army indicate that there are no plans to procure a production weapon, at least for the time being. Presumably the new production facilities required for both guns and ammunition are a factor, coupled with the fact that substantial weight savings are also being achieved by prototype polymer/metal hybrid versions of conventional cartridge cases fired from conventional guns – a technology involving far less cost and risk.
So if both the new carbine and LSAT are out of the picture (at least for the time being), what next? Will the U.S. Army continue to rely on the 5.56mm M4A1 for the foreseeable future? Or will the opportunity be taken to rethink the characteristics of the standard infantry rifle, which will necessarily involve changing the performance requirements of the ammunition? A Congressional study currently underway indicates that the possibility of a change in caliber may be seriously considered.
The Congressional Study
The House of Representatives Report 112-705 on the National Defense Authorization Act for Fiscal Year 2013 was published in December 2012. Section 158, titled Study on Small Arms and Small Caliber Ammunition Capabilities, included the following provisions:
“Not later than 30 days after the date of the enactment of this Act, the Secretary of Defense shall enter into a contract with a federally funded research and development center to conduct a study on the requirements analysis and determination processes and capabilities of the Department of Defense with respect to small arms and small-caliber ammunition that carries out each of the following:
(A) A comparative evaluation of the current military small arms in use by the Armed Forces, including general purpose and special operations forces, and select military equivalent commercial candidates not necessarily in use militarily but currently available.
(B) A comparative evaluation of the standard small-caliber ammunition of the Department with other small-caliber ammunition alternatives.
(C) An assessment of the current plans of the Department to modernize the small arms and small-caliber ammunition capabilities of the Department.
(D) An assessment of the requirements analysis and determination processes of the Department for small arms and small-caliber ammunition.”
Further paragraphs specify that this study shall take into account a number of factors, including current and future operating environments, capability gaps in small arms and small-caliber ammunition identified by the Department, and the results of any studies carried out by the Department of Defense Small Arms and Small-Caliber Ammunition defense support team.
The Secretary is required to submit to the congressional defense committees a report containing the results of this study no later than September 30, 2013.
The story behind this study is complex but of considerable significance.
The Background – NATO Ammunition
The current NATO rifle and machine gun cartridges on which this congressional study will be focusing are the 5.56mm and 7.62mm rounds. The 7.62mm (technically, 7.62×51) was developed in the USA and adopted by NATO in the 1950s in order to obtain one standard, all-purpose small-arms cartridge used by all NATO nations and interchangeable between the weapons of NATO armed forces.
The 7.62mm NATO proved to be hard-hitting and long-ranged, but the experience of fighting in Vietnam began to reveal some disadvantages: it was unnecessarily powerful, requiring heavy guns to fire it, generated too much recoil for automatic rifle fire to be controllable, and the ammunition weight limited the quantity that could be carried, especially important for machine guns. Meanwhile, the enemy was supplied with light and compact Kalashnikov carbines that fired the less powerful 7.62×39 Russian cartridge and were thereby capable of effective automatic fire.
The U.S. forces acquired some lightweight M16 automatic rifles in the 1960s, intended as an interim solution, using a new 5.56×45 cartridge made by Remington. After initial teething problems this gun and ammunition combination proved well suited to the close-quarter jungle fighting and saw increasing use throughout the army, eventually virtually replacing 7.62mm M14 rifles in the U.S inventory. The 7.62×51 ammunition was mainly retained for use in machine guns and sniper rifles.
By the 1970s there was a clear consensus among the NATO nations that a smaller and less powerful cartridge should be adopted to supplement the 7.62mm. At the end of that decade the 5.56×45 was chosen, albeit in a new loading with a longer effective range, known as the SS109 (or M855 in U.S. service). Various automatic rifles and light machine guns were developed to use this cartridge, which weighs only half as much as the 7.62mm round and also generates much less recoil. The effective range was acknowledged to be shorter than the 7.62×51, but it was comparable with the Russian 7.62×39 and the newer 5.45×39 Kalashnikov rounds, and was deemed to be adequate for the battle conditions expected in a European war. In many NATO armies, 5.56mm weapons entirely replaced 7.62mm ones at squad level, with the heavier 7.62mm machine guns being moved back to the support role.
The Small-Caliber Ammunition Problem 1: Effectiveness
The first concerns about the performance of the 5.56mm M855 began to appear after the fighting in Somalia in 1993, when some U.S. troops complained that the bullets were often proving to be ineffective even at short range. Similar anecdotes appeared following the invasion of Iraq in 2003, but were countered by other examples of the ammunition’s effectiveness. It took some time and much laboratory research to discover what was going on. It was found that the effectiveness of the M855 bullet varied considerably, depending on its angle of yaw when it struck the target. Yaw in flight affects all pointed bullets to some degree, but the M855 proved to be unusually sensitive to this, resulting in dramatic variations in its effectiveness.
After this problem was identified, work commenced in the U.S. to develop 5.56mm bullets that would deliver more consistent effects. The U.S. Army wanted at the same time to convert to “green” (i.e. lead-free) ammunition, due to concerns about lead build-up on practice ranges. A protracted development effort during the 2000s eventually resulted in the M855A1, known initially as the LFS (lead-free slug) and subsequently as the EPR (Enhanced Performance Round), which began to enter service in 2010. This replaces the lead core with a copper one but retains the steel tip intended to give the M855 enhanced penetration, although this is larger and is exposed instead of being concealed within the jacket. It is claimed that the M855A1 delivers improved terminal performance and penetration. However, to provide such performance from the short-barreled M4 carbine, the chamber pressure is higher than the M855 (apparently 62,000+ psi instead of 55,000 psi), reportedly resulting in increased barrel wear and a reduced gun life.
In the meantime, the U.S. Marine Corps became impatient with the long development of the M855A1 and acquired an entirely different new loading of the 5.56mm, the MK318 Mod 0 SOST (Special Operations Science & Technology). This is basically a copper-alloy bullet with a lead core in the nose. It is said to provide both more consistent anti-personnel performance and improved barrier penetration – an inherent weakness of the light 5.56mm bullets, which cannot plough through as much material as the heavy 7.62mm.
These new loadings may go some way towards resolving the erratic short-range effectiveness that afflicts the M855. It is unlikely that they will ever achieve NATO standardization, however, since neither of them complies with the wording of the Hague convention of 1899 (subsequently subsumed into the Geneva Conventions), which bans 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.” In neither the M855A1 nor the MK318 does the bullet jacket enclose the tip. U.S. lawyers argue that the Hague wording was intended to prohibit expanding bullets, and as neither of the new 5.56mm loadings are designed to expand they comply with the spirit of the Conventions, but British and some other NATO lawyers take a more literal view of the text.
The Small-Caliber Ammunition Problem 2: Range
An additional and even more serious problem with the 5.56mm became evident in the open-country fighting that has characterized much of the conflict in Afghanistan. The maximum effective range of the NATO cartridge depends very much on the circumstances and particularly on any crosswinds, since the little bullet is relatively easily blown off course at longer ranges as well as shedding energy rapidly. While acknowledging that the gun and ammunition combination is capable of precision long-range shooting in the right hands, many military sources therefore put the practical effective range in the 300-400 meter bracket.
The insurgent forces opposing the ISAF troops quickly noted this shortfall and began to make more use of their PKM light machine guns and SVD rifles rather than the AKM carbines, since these guns fire the old 7.62x54R Russian round, which is at least as powerful and long-ranged as the 7.62×51 NATO. The result is that the normally expected 300 meter limit for most small-arms engagements was suddenly extended to 900 meters, with some reports indicating that more than half of the insurgent attacks were being launched from 500 meters or more. 5.56mm weapons were never intended to cope with such long-range engagements, and they cannot effectively do so.
Furthermore, the 5.56mm weapons are much worse at suppression (one of the primary functions of small-arms), partly because the bullets are less likely to pass close by the target due to wind drift, partly because the sonic bang they make is quieter since that is linked to bullet weight. As a result, 5.56mm fire has little suppressive effect at longer ranges, according to a 2009 British Army study into target suppression in combat.
The result of this range crisis was that ISAF forces rushed their old 7.62×51 weapons back into the infantry squad as quickly as possible, even manually-loaded bolt-action sniper rifles being pressed into service. Thousands of old self-loading M14 rifles were updated and re-issued to U.S. troops, and new 7.62mm rifles and LMGs have been acquired by several armies. The existing 7.62mm FN General-Purpose Machine Gun (M240) in common use by ISAF forces made a welcome return to the front line, but with the most unwelcome consequence of increased weight. Western infantry is already burdened by massive combat loads, and doubling the weight of ammunition belts to be carried just adds to that problem. But as the PM Soldier Weapons Assessment Team reported in 2010: “lethality trumps weight reduction when extended ranges are required.”
To add insult to injury, the insurgents’ PKM machine gun is only about two-thirds of the weight of the M240, despite having a similar performance. Some armies have therefore acquired the FN 7.62mm Minimi (MK48) to replace at least part of the 5.56mm inventory, but that does nothing to reduce the ammunition burden.
In summation, recent combat experience has shown that, even with improvements in effectiveness, which are unlikely to prove acceptable across NATO, the 5.56mm cartridge is inadequate at extended small-arms ranges. This should not have caused any surprise as the little cartridge was never designed for that. In contrast, the 7.62mm does the job, but is too heavy and generates too much recoil. So NATO is left carrying two small-arms suites in two calibers, neither of which is satisfactory in providing the basis for a standard rifle and machine gun weapon system.
What that means on the ground is that infantry patrols routinely carry weapons in both calibers, since they are unlikely to know in advance whether any small arms engagements will be at long range, short range or both. The obvious problem that this causes is that only those with 7.62mm weapons will be able to engage the enemy effectively at long range, while only those with 5.56mm weapons will be well-equipped for close combat such as house-clearing. So in most engagements, only a part of each squad will be fully effective. The two-caliber solution also causes issues with ammunition sharing and resupply.
Studies Into Alternative Calibers
The question implicitly being asked by the congressional study is really this: is there a viable alternative to the existing two calibers? Can one general-purpose cartridge have the characteristics necessary to match or beat the 7.62mm at long range, while weighing a lot less and developing much less recoil? Several studies suggest that this is entirely feasible. Just to focus on the most recent and relevant ones, reports from both ARDEC (the U.S. Army Armament Research, Development and Engineering Center) and AMU (the U.S. Army Marksmanship Unit) point the way forward. Neither report has been released to the public, but some of their findings have become known.
An ARDEC review in 2009-10 examined several different calibers for future infantry rifles in terms of performance metrics that included: penetration; terminal effectiveness; accuracy; initial, retained and striking energy; wind drift; stowed kills; and recoil. 5.56mm and 7.62mm rounds were compared with 6mm, 6.35mm and 6.8mm, in all cases when loaded with lead-free copper and steel bullets to represent the EPR. The outcome of the study was that both 6.35mm and 6.8mm comprehensively outperformed the others in their overall balance of characteristics.
In 2011-12 AMU also carried out a study into the optimum cartridge for a future infantry carbine, and concluded that the cartridge length and diameter should be greater than 5.56×45, the caliber should be 6.5mm and the muzzle energy around 2,500 J. Low-drag bullets would be used to provide good long-range performance, enabling the smaller bullet to catch up with and eventually beat the 7.62mm in terms of retained velocity and energy, flatness of trajectory and wind drift.
It isn’t just the U.S. which is conducting such studies. The Department of Applied Military Science in Canada recently carried out a Small Arms Intermediate Calibre Study as part of their Small Arms Modernization and Small Arms Replacement Projects. They compared the external ballistics of the 5.56mm and 7.62mm NATO with commercially available 6.5mm and 6.8mm rounds of intermediate power, and concluded that the 6.5mm round firing low-drag bullets delivered by far the best long-range ballistics, including resistance to wind drift.
The case for such a general-purpose cartridge was strongly made in a report that emerged from the U.S. Army’s Program Executive Office Soldier in 2011: Soldier Battlefield Effectiveness. This analysis covers a lot of ground but the following quotes concerning the ideal characteristics of future infantry rifles and their ammunition are the most relevant:
“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.”
The Options
Are there any cartridges available off-the-shelf that could provide the basis for the general-purpose round identified by ARDEC and AMU? A survey of existing commercial ammunition indicates “not quite.” There are some powerful 6.5mm cartridges, such as the 6.5×47 Lapua and .260 Remington, which comprehensively outperform the 7.62mm in virtually every respect, but they provide little in the way of weight or recoil reductions. Conversely, there are some smaller cartridges, particularly the 6.8mm Remington and 6.5mm Grendel, which meet the weight targets and are almost good enough but have been handicapped through being limited to the same overall length as the 5.56mm round in order to fit into modified 5.56mm weapons.
On paper, the 6.5mm Grendel can deliver the kind of performance identified by AMU. However, that is only by using a long barrel and firing lead-cored target bullets. A shorter barrel, more typical of current military practice, requires a more powerful cartridge to achieve the same performance. Furthermore, a lead-free bullet will be longer than a lead-cored one of the same weight, thereby extending further into the case and usurping space needed for propellant; this is even more true of tracer bullets. Finally, any new cartridge must be suitable for adaptation to a polymer/metal hybrid case to save yet more weight, but such cases are thicker and thereby reduce the propellant space some more. Add all of these factors together and it is clear that the Grendel, while coming closer than anything else, doesn’t have enough case capacity to deliver the performance needed to replace the 7.62mm.
Where Next?
If the congressional study results in a demand for a standard infantry cartridge a new one will be needed, roughly half-way in caliber, size, weight and power between the 5.56mm and 7.62mm rounds, but with a superior long-range performance due to the use of a low-drag bullet. Analyses of the requirements for such a cartridge keep zeroing in on a caliber of around 6.5mm and muzzle energy of about 2,500 Joules. It would not be difficult to develop such a cartridge and adapt existing rifle and MG designs to fire it.
Despite the emphasis on the ammunition, acquiring new weapons in a new caliber would not be sufficient by itself to obtain the maximum benefit from the improvement in long-range performance. Advanced sights will be needed, capable (as a minimum) of measuring the range and adjusting the aiming point accordingly. Adequate training will also be needed for soldiers to get the most from the systems.
Finally, for those concerned about the cost to change to a new caliber and weapon system, it should be noted that the driver for change is the needs of the dismounted infantry. Other branches of the armed forces could be expected to keep 5.56mm carbines in a self-defense role for the foreseeable future, and most vehicle-mounted 7.62mm machine guns also would not require rapid replacement, so the changeover could be phased over a long period.
The long-running debate over the optimum military small-arms caliber has been growing in volume in recent years, with interest in a new approach being expressed within several NATO armies. Perhaps this congressional study will at last provide the impulse to take some practical steps to resolving this issue.
