The Small Arms Calibre Debate


In an era of ‘shock and awe warfare where a deadly cocktail of sophisticated combat aircraft and smart munitions can deliver unprecedented destructive firepower, any debate about military small arms calibres may seem redundant. However, recent asymmetric campaigns in Iraq and Afghanistan show that collateral damage seriously impedes efforts to win the hearts and minds of the local population, something that has proved essential to the achievement of a wider military and political goals. This not only mitigates against the indiscriminate use of area weapons but reasserts the importance of the humble infantry soldier equipped with small arms capable of neutralising enemy threats with surgical precision. The need to select the optimum mix of weapons and ammunition has understandably re-ignited interest in small arms calibres.

The conflicts in Iraq and Afghanistan also represent the first sustained combat use of the NATO 5.56 mm (SS109 / M855) round selected in 1979. Previously, this calibre had only seen service in Vietnam where most engagements took place at short ranges and seldom beyond 200 metres. This calibre was a controversial choice at the time and despite a series of upgrades remains so today.

The thinking behind 5.56 mm ammunition is simple and compelling: the more rounds a soldier has, the greater his chance of hitting a target. With this in mind, the USA developed a round that would be smaller and lighter than the existing NATO 7.62 mm cartridge. The new calibre utilised a very small bullet (4 grams) fired at a very high velocity (940 meters per second). To compensate for low mass, lethality was dependent on the cavitation effect of the bullet, i.e. the size of the hole created as it passes through a target. The original 5.56 mm round, the US M193, was designed to become unstable upon impact. This meant that it would tumble after hitting a target to create a much larger wound track and thus inflicting increased damage. It was a highly innovative concept that allowed soldiers to carry significantly more rounds for a given weight of ammunition.

When NATO adopted 5.56 mm, reservations about performance were overcome by redesigning the bullet to offer better penetration against armoured plate. This was achieved through greater stabilisation and the addition of a steel core. NATO testing showed that the new SS109/ M855 round could defeat a steel helmet at 500 metres.

It seems hard to believe, but NATO 5.56 mm ammunition did not receive a proper baptism of fire until 14 years after it was adopted. This happened during the US ‘Blackhawk down’ incident in Mogadishu in 1993. US soldiers reported that it had often taken multiple hits to incapacitate a single enemy combatant. British forces may have experienced the same problems during an equally brief but intense skirmish in Sierra Leone during 2000, but in both instances there simply wasn’t sufficient data to draw any conclusions.

However, since military operations began in Iraq and Afghanistan in 2002, a stream of negative feedback concerning 5.56 mm ammunition’s effectiveness has reached the public domain. Much criticism is due to the US Army’s adoption of the short-barrel M4A1 carbine, which has a 14.’5” barrel versus 20” of the standard M16A4 rifle; (a shorter barrel is likely to reduce the ballistic performance of any ammunition). Then, in 2007, operational reports from British troops serving in Afghanistan, supported by the UK MoD’s own analysis, suggested that 5.56 mm ammunition performance was also a problem for British soldiers. Then a secret German report, made public in 2009, showed that the Bundeswehr had experienced the same issues in Afghanistan. Problems with 5.56 mm ammunition fall into four categories:

1. Lack of effective range. More than 50% of infantry engagements in Afghanistan take place at ranges above 300 meters. When 5.56 mm ammunition was adopted, it was believed that 90% of combat engagements would take place under 300 meters. It frequently results in situations where ISAF troops cannot return fire when engaged by enemy snipers. 5.56 mm ammunition is meant to be effective at 500 metres, but combat feedback suggests that this is not the case.

2. Inconsistent lethality. There have been instances where enemy combatants have not been neutralised by 5.56 mm bullets, sometimes despite receiving multiple hits. This has happened at longer ranges, but also, surprisingly, at shorter ranges.

3. Poor barrier penetration. In certain situations, 5.56 mm ammunition has been defeated or deflected by barriers obscuring a target, including car windows, car doors, light masonry and woodwork. Even when a 5.56 mm succeeds in penetrating an intermediate barrier, its energy may be depleted so that lethality is compromised.

4. Inadequate suppressive effect. The UK MoD’s own analysis suggests that insurgent forces are not suppressed by 5.56 mm ammunition, whereas larger calibres have a more notable psychological effect.

Independent testing by US ballistic experts using gelatine blocks to simulate human tissue was conducted to examine lethality concerns. The results showed that NATO 5.56 mm ammunition does not yaw consistently. Sometimes, the bullet will travel straight through a target, like a hypodermic syringe, making an extended hole, but inflicting limited damage and failing to incapacitate. This is consistent with UK reports of malnourished Taliban insurgents running away despite being shot with several 5.56 mm rounds.

The UK MoD responded to criticism in late 2009 by publicly stating that it was entirely satisfied with the performance of Radway Green’s L2A2 version of the NATO standard SS109 5.56 x 45 mm round. Since that time, there have been a number of interesting developments which suggest that the above concerns are more than justified.

The US Army has now fielded an improved 5.56 mm round, the M855A1 EPR cartridge, while the US Marine Corps has developed its own improved ammunition, the Mk 318 SOST MOD 0 round. Both rounds provide American troops with better terminal effectiveness and barrier penetration at all combat ranges. With greater length and mass, they incorporate what is effectively an open tip bullet design enabling them to fragment upon impact. This allows energy to be transferred into the target more reliably, although their legality under the terms of the Hague Convention is questionable.

In August of this year, the UK MoD announced the intention to field its own improved 5.56 mm ammunition, the so-called “Dirty Harry” round, which also offers improved performance thanks to a longer, heavier bullet. Compared to US ammunition, the new UK round does not have an open tip. Although better than the existing L2A2 round and legal, the new round is likely to be less effective than its American counterparts because the bullet does not fragment.

While such improvements are likely to be welcomed by troops on the ground, there is an emerging consensus that 500 meters may be the maximum effective range for all 5.56 mm calibre weapons.

When 5.56 mm ammunition was adopted, future war scenarios envisaged mostly urban combat engagements and limited open country skirmishes, so a maximum range of 300 meters was seen as sufficient. The conflict in Afghanistan has challenged this belief. Vast open planes, high mountains overlooking wide valleys, plus bright sunshine and clear visibility enable small arms engagements to take place at much longer distances. Taliban insurgents already know this and have been using snipers equipped with full-calibre 7.62 mm x 54R ammunition very effectively to engage ISAF troops at ranges well above the capabilities of the latter’s 5.56 mm weapons, typically at 600 meters plus. This suggests the need for small arms that are effective at 1,000 metres.

US, UK and German forces have responded to this threat by readopting 7.62 mm weapons. The previous NATO standard calibre (the 7.62 mm x 51 M80 ball round) was never criticised for a lack of performance. On the contrary, it was only ever supplanted by 5.56 mm x 45 ammunition because the former calibre was felt to be too big, heavy and powerful.

The UK has now acquired a 7.62 mm AR-10 derivative from LMT, the L129A1, as a ‘Sharpshooter’ rifle. Equipped with the latest x6 optical combat gun sights, this weapon represents a significant step-up from the old FN FAL or L1A1 SLR rifle used prior to the adoption of the L85A1 SA80. However, with only 440 in service, they are in scarce supply. The US Army has also reissued a 7.62 mm rifle, the M14, which is used before adopting the M16. Other NATO forces deployed in Afghanistan have also readopted 7.62 mm as well as other large calibre weapons, including .338” sniper rifles and .50” machine guns. Such weapons give troops a significant long-range capability.

The resulting toolbox of small arms is often described as a ‘golf bag’ approach to weapon selection. For short-range and urban use, troops have 5.56 mm weapons. For long-range, open country engagements, they have 7.62 mm weapons.

Proponents of intermediate calibres believe that the dual calibre fleet of infantry small arms is a flawed approach. What happens when soldiers equipped with 5.56 mm weapons come under fire from an enemy at long range? And vice-versa, what happens when soldiers with heavy 7.62 mm weapons are involved in close hand-to-hand fighting? Dual calibre solutions may result in situations where only half of a squad/section can bring their weapons to bear.

The procurement cost of multiple weapon types, the extra logistical burden, additional training requirements and increased weight of typical combat loads suggest that a reduction in ammunition types is desirable. British forces are not merely using 5.56 mm and 7.62 mm ammunition, but also 9 mm, 8.59 mm, 12.7 mm and 12-gauge shotgun shells.

The alternative view is that a single type of ammunition that lies somewhere between 5.56 mm and 7.62 mm could be a better option. A calibre of between 6.5 and 7 mm is seen as the ideal compromise. This point of view is often based on the previous UK development of 7 mm ammunition designed for the aborted EM2 rifle project in the early 1950s. UK MoD tests unequivocally showed that 7 mm was effective at long ranges while weighing less than full-calibre alternatives and with lower recoil. Ballistic experts believe that a modern version of this calibre could even exceed the performance of 7.62mm ammunition at 1,000 meters while weighing 50% less.

The view of many soldiers, especially those with experience of larger calibre ammunition, tends to advocate a wholesale return to 7.62 mm ammunition. The truth is they want a round that is combat-proven and which offers the best possible chance of rapidly incapacitating an enemy. The rule of thumb is the larger the calibre, the more certain the terminal effectiveness. However, any bullet has to hit a target before it can be effective.

The rationale for the adoption of 5.56 mm ammunition was increased hit probability. Few would disagree with the statement that a hit with a small calibre round is always better than a miss with a larger calibre round. The problem with larger calibre rounds is that they have much greater recoil. This can cause shooter discomfort and limit shooting effectiveness. There’s no point in having a large round if you can’t hit the target with it. Perhaps the most important factor in favour of a small calibre is that troops can carry 200 rounds of 5.56 mm ammunition versus only 100 rounds of 7.62 mm ammunition.

To be certain of rapidly incapacitating a target, any bullet (5.56 mm or 7.62 mm) needs to hit the central nervous system (CNS). That means it must strike the head or upper torso, which represents a small and narrow target area. This makes shot placement very important; something that most NATO armies’ training emphasises. With the adoption of optical combat gun sights, marksmanship standards have improved so that more experienced shooters can reliably hit the enemy in the desired spot. While soldiers using 7.62 mm weapons can also shoot more accurately than when they had iron sights, the ease with which soldiers can be trained to shoot accurately with low-recoil ammunition tends to favour 5.56 mm weapons over 7.62 mm weapons.

Perhaps the reason why many soldiers nevertheless prefer 7.62 mm ammunition is because of what it does if it fails to hit the CNS: it makes a much larger hole that is likely to cause rapid incapacitation if not death through catastrophic blood loss. In contrast, if 5.56 mm ammunition fails to hit the CNS, it may not create such a large hole or reliably incapacitate. In many combat situations, stress may prevent the kind of accurate shooting achieved so easily on the range back at barracks.

So does a small calibre give you a better chance of hitting a vital spot or does a larger calibre make up for it in case you don’t? The arguments that favour one calibre over the other is compelling. It is hard to choose which is the right one.

It could be said that neither calibre is ideal. 7.62 mm may be too large given its weight, recoil and energy. The bullet is effective well beyond 1,000 metres, with few soldiers possessing the shooting ability to hit targets at that distance. Conversely, 5.56 mm may be too small, because of range and lethality issues.

Quite possibly, the latest versions of 5.56 mm ammunition may fix performance concerns, but even if this calibre is now lethal at to 500 metres, NATO troops in Afghanistan still need a long-range capability to 1,000 metres. A round smaller than 7.62 mm (e.g. 7 mm) could be made lighter and with less recoil without compromising range or lethality requirements. Similarly, a round larger than 5.56 mm (e.g. 6.5 mm) could also have greater range and more consistent lethality without imposing a significant weight and recoil burden on troops using it.

Those who advocate the ‘golf bag’ approach to fielding multiple calibres argue that an intermediate round has all the disadvantages of both large and small calibre ammunition. The author’s view is that, whether a dual or single calibre solution is preferred, 5.56 mm may simply be too small to achieve consistent results against human targets.

What also makes the small arms debate increasingly relevant is that many UK units are firing more than a million rounds of ammunition per month. The wear and tear on the current fleet of weapons is intense. If the current tempo of operations continues, then the anticipated replacement date for SA80 of 2020 may need to be bought forward. Given long and drawn out procurement timetables, the MoD is already starting to think about what should replace the SA80 family. This makes now a good time to reopen the calibre discussion.

Concerns about ammunition performance are unrelated to the previous criticism of SA80. The story surrounding its conception, development, deployment and failure is an object lesson in how not to procure a weapon system. However, after hundreds of millions of pounds of additional expenditure, the latest versions of SA80, the L85A2 and L85A3, are at least reliable and accurate. Unfortunately, the only accolade that can be attached to this weapon is that it is the world’s heaviest assault rifle. As good as it may now be, there are many newer, better-designed systems that totally outclass it.

One key future design requirement is the need to reduce infantry loads. This tends to favour the retention of small calibre weapons rather than adopting new larger calibre ones. The US Army is already looking at future developments. One particular new system that is attracting interest is the Lightweight Small Arms Technology (LSAT) program. This is centred around case-telescoped and caseless ammunition prototypes that offer between 40%-50% weight reduction versus existing 5.56 mm cartridges. The technology is calibre neutral so it would be easy to change to a larger calibre if required. The increased complexity of LSAT technology means that it needs a considerable amount of further testing before it becomes proven battle-worthy technology. That said, it offers a unique opportunity to select the ideal calibre.

Other new developments include more powerful propellants and lightweight steel and aluminium cartridge cases. These could be lower cost, lower risk options compared to LSAT while saving the same amount of weight.

The most critical factor affecting future weapon and ammunition choices is not user requirements but the politics of change. It is unlikely that any NATO member would independently select a new calibre without endorsement from other allies, especially the USA. However, what the USA decides to do is likely to influence the rest of its allies. It should be noted that the USA unilaterally adopted 7.62 mm and 5.56 mm calibres, effectively forcing the rest of NATO to do the same.

In seeking to field new infantry small arms, the US DoD recently announced that, it would evaluate calibres other than 5.56 mm and 7.62 mm. These include 6.5 mm, 6.8 mm and 7 mm. Given that the USA previously developed two very good intermediate calibre prototypes, the .276 Peterson in the 1930s and the 6 mm SAWS rounds in the 1970s, it could be a case of third time lucky for the USA and NATO.

In summary, many NATO armies have bigger fish to fry than reviewing small arms choices. More helicopters and FRES Utility are certainly a greater priority at this time than any SA80 replacement. So, the most likely scenario is the retention of both 5.56 mm and 7.62 mm weapons. However, if China, Russia or Iran were to adopt an intermediate calibre, this might well be the catalyst for change that is needed to overcome an uneasy status quo.

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