ASSAULT RIFLES AND THEIR AMMUNITION:

HISTORY AND PROSPECTS

Revised 21/10/2006

 

Anthony G Williams

 

Introduction

First, I need to define what I mean by an "assault rifle", as there are various definitions around. The one I use is:

"A military rifle, capable of controlled, fully-automatic fire from the shoulder, with an effective range of at least 300 metres".

This has some clear implications for the ammunition such weapons are chambered for. First, it excludes all weapons designed around pistol cartridges (i.e. sub-machine guns - SMGs) as they only generate around 500 joules muzzle energy and cannot meet the range requirement. Second, it excludes the traditional "full power" military rifle/MG cartridges such as the .303", the .30-06, the 7.92x57 and the 7.62x51 NATO (typically firing 10-12g bullets at 750-850 m/s, and developing around 3,000-4,000 joules), as these are so powerful that their recoil is uncontrollable in fully-automatic fire from the shoulder. Assault rifles therefore need to be designed around a cartridge intermediate in power between pistol and full-power rifle rounds; in practice, approximately in the 1,250-2,500j range depending on the calibre.

Attempts have been made to extend the effective range of SMGs by developing more powerful cartridges for them. However, there is a limit to the degree to which this can be achieved as the basic API blowback mechanism used by most SMGs is not suited to high-powered ammunition. Attempts have also been made to design automatic rifles around full-power cartridges, perhaps the most famous example being the German FG 42 paratroop rifle in 7.92x57. Some of the early rifles in 7.62x51 NATO, such as the American M14, were also capable of fully automatic fire, but the recoil problem made them incapable of accurate fire on full-auto and they cannot be classified as assault rifles.

There have been two contrasting approaches to the design of a suitable intermediate cartridge with the appropriate compromise between long range and light recoil. One is to retain the same 7.6-7.9mm calibre as the full-power round, but with a shorter cartridge case firing a lighter bullet at a lower muzzle velocity (lets call these "full calibre assault rifle", or FCAR, rounds). The other is to reduce the calibre while retaining the same, or a higher, velocity (reduced calibre, or RCAR rounds).

FCAR rounds score well in the traditional methods of measuring stopping power (which are dominated by calibre and bullet weight) and also by being less affected by the bullets striking foliage etc on their way to the target. However, they have a relatively steep trajectory and a rapid velocity loss due to the short, fat bullets, which quickly reduces their effectiveness at long range.

A decision to reduce the calibre raises the immediate question; by how much? At the large end of the RCAR scale (7mm), bullet weight and muzzle velocity can be much the same as in the FCAR cartridges, but the better ballistic coefficient due to the longer and more slender bullet will reduce velocity loss and improve long-range performance. However, there is potentially some loss in stopping power. As the calibre decreases, so the recoil and the ammunition weight become lighter and the velocity can be higher, thereby flattening the trajectory; all good things. The downside is that the stopping power becomes more controversial (relying on velocity rather than calibre and bullet mass; which according to combat reports sometimes works, sometimes doesn't) and the long-range performance begins to decrease again as small-calibre bullets generally have poorer sectional density ratios, and thereby ballistic coefficients, than large-calibre ones.

Different nations have made different choices in developing assault rifles, and the purpose of this article is to describe and analyse them in order to examine the future prospects for this type of weapon.

Development before World War 2

The elements of an assault rifle were in place surprisingly early in the history of automatic weapons. Self-loading rifles were developed before the end of the 19th Century and the first selective fire (semi or full auto) rifle using a medium-power cartridge was probably the Italian 6.5mm Cei-Rigotti, developed between 1900 and 1905, but this was not adopted. Mannlicher introduced their m/1901 carbine in a purpose-designed 7.65x32 calibre, but the loading was relatively weak and it also was not adopted.

Small-calibre rifle cartridges were also in use or under development for military purposes. The USN's 6mm Lee of 1895 is probably the best known, but the curious 5.2mm Mondragon of 1894 was also made (the odd shape resulting from an internal piston to give the bullet an initial kick up the barrel) and the 5mm Sturtevant was being developed towards the end of WW1.

From left to right: 7.62x51 for scale, 6mm Lee, 5.2mm Mondragon, 5mm Sturtevant

The first service weapon which can be identified as conforming to the specification of an assault rifle dates back to the First World War; the Russian Federov Avtomat of 1916.

This was a selective fire weapon using a short-recoil action and was chambered for a military rifle cartridge of intermediate calibre and power - the 6.5x50SR Arisaka - large quantities of Japanese rifles in this calibre having been acquired by Russia. This was an excellent choice, as the cartridge combined moderate recoil with a good long-range performance, but only about 3,000 Avtomats were made. They were used in action in the Russian Civil War and thereby earned their place in small-arms history.

The French also nearly made it into the record books with the first selective-fire rifle using purpose-designed intermediate ammunition. During WW1 they made some use of the semi-automatic Winchester Model 1907 in .351 and .401 Win SL (self-loading) cartridges; the rifle design was very simple, being blowback only. While these were mainly used by aircrew, in 1917 France placed an order for 2,200 of an automatic version of the M1907 for use by special assault soldiers. At the same time, they were modifying the .351 SL cartridge by necking it down to accept an 8mm bullet, creating the 8mm Ribeyrolle. The war ended before anything could come of this.

Interest in assault rifles on the part of the major powers then largely disappeared from view until the Second World War, although experiments continued in some smaller countries. Switzerland developed the Furrer short-recoil carbine in 7.65x35 in 1921 and made a 7.65x38 cartridge in the late 1930s, and in the early 1930s Denmark made limited numbers of the delayed-blowback Weibel (or Danrif) assault rifle in 7x44 calibre. In 1939 a light automatic weapon was advertised in Greece in a 7.92x36 calibre, apparently based on a shortened and neck-out 6.5mm Mannlicher case.

Elsewhere at this time, the prevalence of trench warfare and the associated close fighting had focused attention on short-range automatic weapons, in complete contrast to the prewar obsession with accurate long-range rifle fire. This resulted in three different lines of development: pistols which were modified with longer barrels and stocks and sometimes adapted to fully-automatic fire; purpose-designed SMGs; and the Pedersen Device (which replaced the bolt in the US Springfield Rifle with an automatic mechanism to fire small .30 cal (7.62x20) rounds developing less than 400 joules; it was never used in anger). 

Pistol-based carbines were a natural extension of the occasionally recurring fad for equipping pistols with detachable shoulder stocks in order to permit more accurate aiming. Longer barrels further extended the effective range (partly through increased velocity, partly because of the longer sight base) and so weapons such as the Mauser C96 and P08 produced carbine derivatives, usually only capable of semi-automatic fire. These were relatively expensive to make, however, so the future in short-range automatics lay with the much simpler API blowback SMG. The first of these (if you discount the curious twin-barrel Villar Perosa) was the Bergman MP18 in 9x19 Parabellum calibre, which was the ancestor of the Thompson, the MP 38/40, the Sten Gun, the PPSh and so on.

Attempts to improve the power and range of the small automatics, such as the use of the 9x25 Mauser Export round in the Solothurn and Kiraly SMGs (which saw some service), did not catch on. The late-WW2 efforts in Finland, producing such cartridges as the 9x40 Lilja and the 9x35 Lahti, were no more successful. In fact, despite the evidence that most shooting during WW1 was at short range, armies continued to show an interest in full-power rifle/MG rounds. The Japanese Army even planned to replace their 6.5x50SR cartridge with a new 7.7x58 calibre, although they never completed the changeover. The Italians were similarly caught at the start of WW2 part-way through a change from their 6.5x52 Mannlicher-Carcano rifle to a 7.35x51 calibre.

Why was this? Probably because the need for a full-auto rifle was generally resisted, on the grounds of economy (automatic rifles being much more expensive and requiring more maintenance than bolt-action ones), and also the fear that soldiers would just spray ammunition around at a great rate, causing increased cost and supply problems (this latter concern was, of course, fully justified, but has been addressed by improving supply arrangements). So even the one nation wealthy enough to afford an automatic rifle - the USA - restricted the M1 Garand to semi-auto fire, and full-power rounds biased towards MG use prevailed. Incidentally, the USA did of course have the Browning Automatic Rifle in service, but that was too heavy to be a rifle replacement and was used as a light machine gun.

There had been some efforts towards considering intermediate calibres, with the US Ordnance Board sponsoring comparative trials in the early 1930s of the effectiveness of different rifle cartridges using anaesthetised pigs and goats to assess wounding effectiveness. They concentrated on a .25 (6.35mm), a .276 and the existing .30. The .25 (8g at 820 m/s, for 2,700 joules) most impressed the testers, but the Board chose the .276 Pedersen (7x51) a medium-power round developing 2,400 joules, which would have made an effective assault rifle cartridge. At this point, the top brass insisted on the new rifle being chambered for the .30-06 (7.62x63), so another opportunity was lost.

Rounds for early automatic rifles: the 6.5x52 Carcano, 7.65 Mannlicher Carbine, .30 Pedersen, 8mm Ribeyrolle (replica), Swiss 7.65x35, .276 Pedersen, Swiss 7.65x38 with bullet alongside, 9x40 Lilja, 9x35 Lahti

There was one rather odd American development not followed by any other country - the M1 Carbine. This was a light, semi-automatic rifle chambered for an intermediate, straight-cased 7.62x33 round. It was not originally intended for front-line troops, but more as a self-defence weapon for second-line units, on the sensible grounds that it was much easier to shoot accurately than a pistol. The M2 version came with a full-auto option, and thereby comes close to our definition of an assault rifle, but the cartridge was rather weak and the light, blunt-nosed bullet lost its modest velocity too quickly.

World War 2 and after - the Assault Rifle Emerges

The modern line of assault rifle development started with the Germans. Various experimental cartridges from 7mm to 8mm calibre were tried, and even before WW2 one gun - the Vollmer Maschinenkarabiner M35 - was built around a 7.75x40 Geco cartridge. In 1938 Polte were given a contract by the Heereswaffenamt to develop a new, short-cased infantry cartridge. After much development work, this resulted in the final version of a new round, adopted in May 1942. This followed the FCAR route, shortening the usual 7.92x57 K98 rifle/MG case to 33mm, and loading a lighter bullet at a reduced velocity. Keeping the same calibre was simply a matter of production convenience.

The MKb42(H) by Haenel and the MKb42(W) by Walther were designed around the new cartridge and produced in some numbers for field testing. This led to the development of the Haenel MP43/44 (later renamed StG 44 for Sturmgewehr or assault rifle).

Despite initial opposition from Hitler, this was the weapon the Army wanted to back-up their MG 42 GPMGs, and it was produced and used in quantity. However, the end of the war stopped the direct line of development of this significant weapon.

Next to emerge was the Soviet Simonov SKS, made in large numbers in various countries but now almost forgotten due to the fame of its successor, the Kalashnikov AK. Both weapons were chambered for a new 7.62x39 M1943 cartridge, but the SKS was not an assault rifle, being capable of semi-automatic fire only.

There is still some sensitivity about the connection between the AK and the StG 44, but two things are clear; despite the apparent similarity, the AK was not a direct copy as it uses a quite different mechanism, but on the other hand Kalashnikov and his team must have known about the StG 44 (tens of thousands must have been captured) and it is difficult to believe that they were not influenced by it, even if only to take it as a starting point for improvement.

The 7.62x39 cartridge, however, was definitely inspired by the German 7.92x33; examples of the Mkb42(H) carbine and its ammunition were examined by a Technical Council in July 1943 and the OKB-44 design bureau was given the job of producing a round of similar but superior characteristics, quickly coming up with the M1943.

It should perhaps be noted that the term "AK-47" was applied by the Russians only to the pre-production version of the gun, of which a few hundred were made for troop trials between 1947 and 1949. Modifications were then made to the design before it was formally adopted as the AK (Avtomat Kalashnikova, or automatic [rifle] by Kalashnikov). However, the production version has always been known popularly if inaccurately in the West as the AK-47.

The AK and its ammunition (also used in the RPD light MG) so dominated the assault rifle field until the late 1960s that it is sometimes difficult to remember that there were other developments, one of which saw service. This was the Czech vz52 rifle chambered for their 7.62x45 (after earlier experiments with a 7.5x45), a superior cartridge to the AK's in terms of range, but it was soon replaced by the vz52/57 (chambered for the 7.62x39) in the interests of commonality with the rest of the Warsaw Pact. The vz52 was only semi-auto, but the Czechs were working on a selective fire weapon based on the round when the changeover to the Russian calibre took place; this assault rifle was the vz58.

Other nations also experimented with short-case FCAR rounds, particularly the French and the Swiss. Cartridges such as the Swiss 7.65x38 MP and 7.5x38, the French 7.65mm Model 48 (7.92x35 - the French also experimented with calibres up to 9mm), the Danish 7x36 Otterup and the unusual Spanish 7.92x40 CETME Model 53 (which used a lightweight but highly streamlined bullet) were all unsuccessful contenders during the 1950s.

Another which very nearly saw service was the British EM2 bullpup rifle

EM-2 (above)

TADEN GPMG (left) and 7.92mm Roman Korsac rifle, which predated the EM-1 and EM-2(below)

initially chambered for a new 7x43 cartridge (later slightly modified as the .280/30) which fired its 8.4g bullet at 730 m/s, for a muzzle energy of 2,240 joules. Unlike the AK 47, which continued to be supplemented by the full-power 7.62x54R Nagant cartridge in MGs and sniper rifles, this was a carefully-judged attempt to produce a weapon which could replace both the 9mm SMG and the full-power .303 rifle in one compact package. A GPMG based on the Bren mechanism but with belt feed, the TADEN, was also developed to use this round and replace both the Bren and the Vickers MMG. It appears to have been very successful and other NATO countries (Canada and Belgium, at least) were very interested in the concept. The British and Belgians made great efforts to meet the objections of the US Army, who thought it wasn't powerful enough, first by stepping up the loading to 2,700 joules, then by developing a longer cartridge (the 7x49 - which actually saw service with Venezuela in the FN FAL rifle). Despite this, the Americans insisted on NATO adopting a common round which had to be of .30 calibre and powerful enough to replace the .30-06 in MGs - which meant by definition that it could not be used in an assault rifle. So the 7.62x51 was adopted, which apart from being half an inch shorter than the .30-06 cartridge represented no progress whatsoever over this fifty-year old design.

 

Unsuccessful postwar experiments: 7x36 Otterup, 7.5x38 Swiss,7.5x45 Czech, 7.5x43 French CRBA, 7.92x40 CETME, .280/30 EM-2, 7mm Compromise, 7.62x47 T65 (predecessor of the 7.62x51 NATO), 7.62x51 with CETME bullet.

American experiments were made in the late 1950s with a range of smaller calibres, such as the .22/30 NATO, the .25" Winchester (6.35x48), the .25/30 NATO (6.35x51) and the .27 NATO (6.85x51), but these led to nothing.

Some experimental US rounds of the 1950s: .223 Remington (for scale), .224 Winchester E2, .25 Win FA-T 116 (6.35x48), .25 Win Duplex FA-T 127 (6.35x53), .22/30 Homologous (5.56x51), .27/30 Homologous (6.8x51), .25/30 Homologous (6.35x51), sectioned 7.62x51 M198 Duplex (which actually saw service).

Frustratingly for the intermediate-calibre supporters, the US Army realised after initial experience in Vietnam that they had made a mistake and cancelled further production of the M14 (which had anyway experienced serious production quality problems). Inspired by experimental work which showed the efficiency of small-calibre rifles, they went to the other extreme in adopting the M16 rifle and its tiny .223 (5.56x45) cartridge, developed from Remington commercial hunting rounds which had been designed for taking small game such as rabbits. This was actually only intended to be an interim purchase pending the perfecting of the SPIW flechette rifle (see below) but as this never happened, the 5.56x45 became the US Army's standard rifle cartridge by default. Much controversy arose about its effectiveness in stopping a determined enemy, but what was clear was that the long-range performance of the little bullet (designated M193) was poor. In the next competition for a new NATO rifle cartridge held in the late 1970s, the 5.56mm was duly adopted but in the new Belgian SS109 loading (M855 being the US version), which has a heavier bullet at a lower muzzle velocity and thereby achieves a better long-range performance and penetration - although its terminal effectiveness on human targets has been even more critically questioned.

Rather surprisingly, the Russians followed suit and adopted a new 5.45x39 7N6 cartridge for their next-generation rifle, the AK 74. This is no more powerful than the 5.56 NATO although it does have an exceptionally good aerodynamic form achieved partly by a hollow bullet tip which sometimes bends on impact and thereby encourage tumbling in the target's body. Despite this feature, it is understood that in some quarters the older M1943 round is still preferred.

More recently, the Chinese have begun to introduce a 5.8x42 calibre for assault rifles and LMGs. The ballistics seem little different from the 5.56mm and 5.45mm weapons, although it is claimed that it outperforms both of them, with penetration superior to the SS109, a flatter trajectory, and a higher retained velocity and energy downrange. The differences are only marginal, however, as the standard rifle round is only loaded to 41,500 psi chamber pressure, compared with 55,000-62,000 for the 5.56x45. Furthermore, the emphasis in the bullet design has been the penetration of body armour; its hardened steel core will punch through 10mm armour plate at 300m, which is in the same class as steel-cored 5.56mm AP rounds. A heavier loading of the 5.8x42 also exists, for use in the GMPG and sniper rifles.

Intermediate service cartridges: 6.5mm Arisaka, 7mm Medium, .30 M1 Carbine, 7.92mm Kurz, 7.62mm AK-47, 7.62x45 Czech, 9x39 Russian (silenced AP - replica round), 5.56x45 SS109, 5.45x39 AK-74, 5.8x42 Chinese

Finally, the 5.7mm FN has achieved some sales, in both the FiveSeven pistol and the P90 SMG. However, despite its improved range performance, this 5.56x28 cartridge only develops 550 joules and is really a 9mm pistol round replacement, so doesn't qualify as an assault rifle. The rival HK 4.6x30 and Chinese 5.8x21 are even less powerful.

Experimental Efforts

Despite the domination of the 5.56mm NATO round (in much of the world) and the Kalashnikov family (in the rest), experiments with new assault rifle and ammunition concepts have of course continued, even with the occasional competition being held. Some of the experiments have been with conventional ammunition, others have been more exotic.

Perhaps the most interesting and instructive series of experiments took place in the UK in the late 1960s, when thorough attempt was made to design an ideal military small-arms round. This started with calculations of the bullet energy required to inflict a disabling wound on soldiers with various levels of protection. The energy varied depending on the calibre, as a larger calibre required more energy to push it through armour. For example, it was calculated that while a 7.62mm bullet would need 700 joules to penetrate modern helmets and heavy body armour, a 7mm would require 650j, a 6.25mm 580j, a 5.5mm 500j and a 4.5mm 320j (this last figure looks wrong and should probably be 420j). This figures applied at the target; muzzle energies would clearly have to much higher, depending on the required range and the ballistic characteristics of the bullet.

A range of "optimum solutions" for ballistics at different calibres was produced. These resulted in muzzle energies ranging from 825 joules in 4.5mm to 2,470j in 7mm. More work led to a preferred solution; a 6.25mm calibre with a bullet of 6.48g at 817 m/s, for a muzzle energy of 2,160 joules. The old 7mm EM2 case was necked down to 6.25mm for live firing experiments, although had the calibre been adopted a new cartridge would probably have been designed. Tests revealed that the 6.25 cartridge matched the 7.62 NATO in penetration out to 600m and remained effective for a considerably longer distance, while producing recoil closer to the 5.56mm.

As related in The .256 British, at much the same time, the US Army was looking to develop a new squad automatic weapon (SAW). The 7.62mm was too powerful, the 5.56mm didn't have a sufficiently long range, so a 6x45 round was developed which proved satisfactory but was not adopted because of concerns about putting a multiplicity of calibres into service. A light-alloy cased version of this round was also produced, with the length extended to 50mm to make up for loss in capacity caused by the need to line the inside of the case with fire-resistant material (light alloy having a tendency to catch fire). The Russians in the 1990s also unsuccessfully developed  various new 6mm cartridges, but these were considerably larger and more powerful than the 5.45mm, intended to be used in long-range MGs and sniper rifles.

The Swiss experimented with at least two cartridges in the late 1970s before adopting the 5.56mm NATO; the 5.6x48 Eiger and 6.45x48 GP 80. The 5.6mm fired a 3.7g bullet at 1,050 m/s for 2,040j (considerably more than the 5.56mm NATO) while the 6.45mm managing to propel its 6.3g bullet at 900 m/s for 2,550j. Both rounds were based on the wide 7.62x51 NATO case and were therefore considerably larger than most other intermediate rounds. With the benefit of hindsight, a heavier bullet at a more moderate velocity might have provided a better general-purpose loading for the 6.45mm.

Some experiments since the 1970s: 6mm SAW, 6mm SAW aluminium-cased, 6.25mm British, 6.45mm Swiss, 6.5x43 German, 6.8x43 Remington SPC (commercial soft-point bullet loading: military bullets are shorter to match the overall length of the 5.56x45), 6.5mm Grendel, 5.56x45 for scale

Despite concerns about the stopping power of the 5.56mm, some experimenters have worked with even smaller calibres. The British proffered a 4.85x49 (actually, 5mm) round for the NATO contest which chose the 5.56mm, the H&K; G11 (described below) used a 4.7mm. Calibres of 4.6, 4.3, 3.5 and 3mm (and possibly more - or less) have been tried, mainly during the 1960s and 1970s. It is difficult to imagine that such cartridges could do anything to improve on the 5.56mm's range and stopping power. There is also the capillary problem with the really small bores; any water which gets into the barrel will be difficult to dislodge. A couple of interesting experiments were the 4.6x36 HK for the HK36 rifle (not to be confused with the current 4.6x30 for the HK MP7, nor with the current HK G36 5.56mm rifle), which featured a 'spoon tip' to the bullet to encourage tumbling on impact, and the US 5.56mm FABRL, which combined a light-alloy case with a lightweight but well-streamlined bullet fired at high velocity.

Experimental cartridges under 6mm: FN 5.56x45 APDS, .12 US (3x47), 3.5x50 FN, 4.3x45 German, .17 US (4.3x46), 4.6x36 HK/CETME (with spoon-tip bullet), 4.85mm British, 5.56x38 FABRL, 5.6mm Eiger

The more exotic experiments have proceeded in different directions, with different aims in mind. Some attempts have been made to improve the hit probability of conventional 7.62mm cartridges with multi-ball loadings, using two (duplex) or three (triplex) lightweight bullets stacked on top of each other. One of these, the US M198 duplex, was even accepted for service. A "salvo-squeezebore" (firing several stacked conical projectiles which were squeezed down to a smaller calibre by a muzzle attachment) was developed for the .50" BMG, and a version in 7.62x51 NATO was also tested with unsatisfactory results.

Others have attempted to achieve the same aim by using flechette technology (in principle, a scaled-down APFSDS tank gun round - APersFSDS?) to achieve an extremely short flight time and flat trajectory resulting from a muzzle velocity of around 1,400 m/s. This gives such weapons an almost ray-gun like performance, with allowances for range, wind-drift and target movement being hardly needed at normal battle ranges. This was first seriously proposed in the American Special Purpose Infantry Weapon (SPIW) project of the late 1960s, in which several manufacturers produced weapons using basically similar ammunition firing 1.8mm diameter darts. Accuracy was not as good as conventional rifles, however, and the cost of the ammunition was very high. Attempting to achieve everything in one weapon by building in a grenade launcher didn't help, either, and the project foundered.

Experimental US flechette rounds: 5.56x45 for scale, sectioned 5.6mm XM216, 5.6mm XM144, 5.6mm XM110, 5.6mm XM645 (all part of the SPIW programme), .330 Amron Aerojet (alloy case, with three flechettes)

Flechette weapons were revived by two of the competitors in the Advanced Combat Rifle (ACR) contest of the late 1980s. This contest was intended to improve the poor hit probability achieved by average soldiers in the stress of battle, which using the M16 was only guaranteed (pH = 1.0) at up to 45m, and dropped to a pH of 0.1 (one shot in ten) by 220m. The theory was that firing three slightly dispersed shots in quick succession should enable the pH to be doubled, and several different weapon concepts were prepared.

The Colt ACR contender was simply an improved M16A2 firing a duplex cartridge, H&K; submitted the caseless G11, while AAI and Steyr (below) offered weapons firing flechette rounds, the Steyr ammunition being plastic-cased.

Although all of the weapons apparently performed well and did increase the hit probability, none of them managed to double it.

Finally, there were several attempts at a multi-flechette weapon; one example being the .330" Amron Aerojet, which contained three flechettes within its 8.38x69 light-alloy case.

Other experiments have looked at different cartridge types to suit novel gun designs. Perhaps the most bizarre was the US "folded" ammunition, stemming from a desire to make the cartridge as short as possible to speed up the firing cycle. These were made in many calibres, including 5.56mm. Another try was the Hughes Lockless (also made in calibres up to 30mm) which concealed the bullet within a flat, rectangular plastic case. This was designed to slot sideways into a simple gun action. Other oddities were the Belgian Schirnecker rounds of various sizes which fired saboted bullets from straight steel cases, and the 9/4mm Kaltmann in which the plastic cartridge case was expected to follow the bullet down the barrel.

Exotic attempts: 5.56x45 with Monad bullet, 4.5mm Schirnecker, 9/4mm Kaltmann (development round, with part-metal case), 5.56mm Folded, 5.56mm Hughes Lockless, 5.56mm US caseless, 6mm Voere caseless, early HK G11 4.7x21 rounds, final G11 4.7x33

The closest to adoption of all of the exotics was the caseless cartridge, in the form of the Heckler & Koch G11 rifle (below). It was actually about to be adopted by the German Army to replace the 7.62mm G3 (Germany never having adopted the 5.56mm NATO) when the Cold War ended and the Berlin Wall came down. Military re-equipment spending promptly halted. H&K were financially ruined by the cancellation of the G11 and fell into the hands of Royal Ordnance, where they have earned their keep by sorting out the long-running problems of the British Army's SA-80 rifle, but that's another story. In 2002, HK were taken back into German ownership. Caseless 5.56mm rounds had also been experimentally developed around 1970 in the USA, and the Austrian firm of Voere even managed to sell some commercial caseless rifles - they are still offered.

Caseless ammunition has obvious benefits. It is much lighter and more compact (no metal case), and it is unnecessary to arrange for the extraction and ejection of the fired case (perhaps the principal source of weapon jams). The disadvantages are that it is much more vulnerable to damage (which H&K; got around by supplying the ammo in sealed plastic see-through packs which clipped directly to the gun) and the propellant is more likely to "cook-off" in a hot chamber; a problem exacerbated by the fact that a brass cartridge case makes an efficient job of transporting heat from the gun. Despite this, H&K; (or rather Dynamit Nobel) cracked the problem by developing a new heat-resistant kind of propellant and produced a battle-worthy weapon.

Current plans

Despite all of these experiments, new weapons currently planned for adoption are relatively conventional, at least as far as the assault rifle element is concerned. The US Army currently appears to favour the M4, a carbine version of the M16 with a shorter barrel.

 

The H&K; G36 (above) is probably the current market leader and was adopted in modified form as the rifle element of the OICW, (below) since shelved due to weight problems.

 

The G36 also formed the basis of the XM8, which was being developed in several versions to replace the M16/M4 family and the M249 SAW. However, the US Army's adoption of this was first held up by a decision to reopen the selection to competition, then that competition was put on hold pending consideration of other services' needs, then it was delayed again to take account of the lessons from Iraq and Afghanistan, before (in early 2006) being deferred for at least five years, apparently because the National Audit Office criticised the project for offering insufficient benefits for the expenditure involved. However, the US special forces (SOCOM) are going ahead with the adoption of the FN SCAR rifle/carbine in Light (5.56x45) and Heavy (7.62x51) versions.

These US weapons are going against the trend by having a traditional instead of bullpup layout. The traditional layout is preferred by many as it is easier to switch sides and use left-handed, but it carries the penalty of a shorter barrel for the same overall length. Compactness for manoeuvring weapons in AIFVs or helicopters, or for use in close-quarters fighting, is evidently considered important as most new developments are bullpups, and traditional designs are now favouring short carbine barrels.

New bullpups include the Chinese QBZ-95, the Israeli Tavor (right), the SAR-21 from Singapore (below) and the FN2000 (bottom). The last of these (a modular system, as is common nowadays, with various add-ons being optional) gets over the left-handed problem by ejecting the spent cases forwards and downwards.

All of these weapons except for the 5.8mm QBZ-95 are chambered for the usual 5.56x45 NATO. The problem with short barrels in this calibre is that they reduce the muzzle velocity, and the 5.56mm bullets rely on a high impact velocity to tumble and fragment. At lower velocities the bullets will not fragment and much of the wounding potential is lost. In the normal 20" (51 cm) barrel the fragmentation distance is 150- 200m, but in the short carbine barrel it can be as low as 50-100m, depending on the bullet. The US Army's current preference for the short-barrelled M4 carbine has restarted this argument, with the terminal effectiveness of the 5.56x45 becoming controversial once again.

The USA spent some time developing the OICW (Objective Infantry Combat Weapon), also known as the SABR and the XM29. This combined a short-barrelled 5.56mm with a self-loading low-velocity 20mm gun. The heart of the weapon was a laser rangefinder coupled to a fire-control computer linked to optronic sights and an electronic fuze-setter. This complex and extremely expensive fire control system meant that the gunner could fire a 20mm shell to explode directly over the target at anything up to 1,000m. However, it proved impossible to reduce the weight from 8.2 kg to the target 6.8 kg, so development was shelved in favour of the XM8 and the XM25, which is a 25mm self-loading grenade launcher.

The French are experimenting with a similar (and even bulkier) system, the PAPOP (below) which has a 35mm grenade element, while the Australians are basing theirs on the Metal Storm technology, in which the grenade shells are stacked within the barrel. Such systems are undoubtedly impressive but whether they will still work when they are several years old, especially after having being kicked around a combat zone for a few weeks, remains to be seen.

The Lessons - and the Future

What conclusions can we draw from all this, and what does the future hold?

Two conclusions about the present situation seem pretty clear. One is that there would be financial and logistical benefits in having only one military rifle/MG cartridge. The other is that it wouldn't hurt to have a rifle cartridge with more reliable hitting power than the 5.56mm. As it happens, both conclusions point in the same direction; towards a cartridge intermediate in power between the 5.56mm and 7.62mm NATO.

Such an "ideal" cartridge would need to combine a long-range effectiveness comparable with the 7.62mm, with a recoil light enough to permit controlled, full-auto fire. Is it possible to achieve this? The evidence suggests strongly that it is. The British aimed to do this with the 7x43 cartridge half a century ago, and by all accounts succeeded admirably. This gives us an upper calibre limit. I don't think that a useful increase in performance over the 5.56mm can be achieved with anything smaller than 6mm calibre, which gives us the lower limit. We need to specify a bullet sectional density ratio of about .230 in order to retain velocity better than the 7.62mm (whose 9.33g bullet has an SDR of 0.217 - the 5.56mm SS109 bullet has an SDR of 0.174,and the new 5.0g Mk 262 is 0.220) and thereby deliver the long-range performance we want. We also need a muzzle energy of no more than 2,500 joules to provide the right balance of power and recoil. Taking into account that smaller calibres need less energy to penetrate armour, this works out as the following range of choices in common calibres:

7mm/.276": bullet weight 8.4g (130 grains) at 770 m/s (2,525 fps) = 2,500j

6.85mm/.270": bullet weight 7.9g (122 grains) at 784 m/s (2,570 fps) = 2,430j

6.5mm/.258": bullet weight 6.9g (106 grains) at 820 m/s (2,690 fps) = 2,330j

6.35mm/.25": bullet weight 6.5g (100 grains) at 834 m/s (2,736 fps) = 2,260j

6mm/.24": bullet weight 5.9g (91 grains) at 854 m/s (2,800 fps) = 2,150j

Any of the above options would do, but for the sake of argument let's take the 6.5mm. A cartridge of this calibre would be smaller than the more powerful 6.5mm Arisaka. If a similar case diameter were retained then length could be reduced to about 45mm. In fact, the case diameter and length would be similar for all of the above cartridges.

So, we have our ideal military general-purpose assault rifle and MG cartridge - the "6.5x45 GP" - and we could have had it many decades ago. What are the chances of such a cartridge being adopted now? Some hopes were raised recently by the introduction of a couple of new rounds which (more or less) fit the above criteria. One is the 6.8x43 Remington SPC (Special Purpose Cartridge) which fires a 115 grain bullet at 2,650 fps from a 16.5 inch barrel (7.45g at 808 m/s = 2,430j); very similar to the 'ideal' 6.85mm listed above. The cartridge case is based on the old .30 Remington commercial round, with a larger diameter than the 5.56x45 (but smaller than the 7.62x51) to increase the case capacity. Overall length is kept within the 57mm limit to fit in the M16 action. This round develops 55% more muzzle energy than the 62 grain SS109/M855 loading at the muzzle, rising to 84% better at 550m due to its superior ballistic coefficient (the SD is 0.214). The trajectory matches that of the 7.62x51 M80 ball out to 500m, and is only 10cm low at 600m. The development of this round was sponsored from within the US SOCOM (Special Operations Command) who were looking for a more powerful cartridge than the 5.56mm, and it has reportedly been successfully tested in action.

More recently, another challenger emerged in the form of the 6.5mm Grendel (6.5x38).This uses a slightly fatter case (the same diameter as the 7.62x39 Russian) which enables it to be shorter, thereby leaving space for longer and more aerodynamic bullets. This enables it to fire a 123 grain Lapua Scenar bullet at 2,530 fps (8.0g at 770 m/s: 2,370j) from a 16 inch barrel, with a far superior ballistic coefficient to the 5.56mm Mk 262 or 6.8mm bullets (SD 0.252). In a longer rifle or MG barrel this provides trajectory and velocity loss figures to match or better those of the 7.62x51 M80 ball round.

There did appear to be some hope that the planned US programme to replace all of their 5.56mm rifles, carbines and MGs with a new family of weapons provided an opportunity to consider a new round like the 6.8mm Remington or 6.5mm Grendel. However, the effective cancellation of this programme now makes this extremely unlikely. Instead, a new Mk 262 loading  for the 5.56x45 has been introduced which, although so far only in limited service (mainly with special forces), appears to have significantly improved the effectiveness of the cartridge from short barrels.

Attention is now focusing on the next generation of infantry small arms, for 2020 and beyond. The UK has already determined that the SA80 family will serve until that date, and has started a project to consider its replacement. Some indication of the form which the ammunition for this might take is beginning to emerge. Flechette rounds have been tried and rejected, at least for now, despite their impressive long-range performance (the Steyr ACR round started at 1,500 m/s at the muzzle and was still travelling at over 1,200 m/s at 1,000m). But the previously rejected caseless techology is being revived, along with plastic-cased telescoped rounds.

The USA is undertaking a Lightweight Small Arms Technologies development programme, with the aim of halving the weight of the current 5.56 mm M249 (FN Minimi) LMG and its ammunition. Two different cartridge designs are being tested, shown here in comparison with the 5.56x45 (top). In the middle is a polymer-cased telescoped round (by ARES), and below that a caseless round (by ATK) based on HK G11 technology. The linked polymer-cased rounds are showing a 33% reduction in weight over conventional 5.56x45 ammunition, the caseless rounds a 51% reduction. The initial calibre and ballistics have been chosen to match the 5.56x45 SS109/M855 for comparison purposes, but in parallel with this, research is being carried out into using the weight savings to produce a "Company" MG which might replace both 5.56mm and 7.62mm MGs.

This programme might therefore result in an MG no heavier than the 5.56mm weapons but with more powerful ammunition to enable it to replace 7.62mm MGs as well. If so, the possibilities of building a new assault rifle round this "intermediate" MG round are obvious.

We may also see something more radical; perhaps a large-calibre weapon following on from the current grenade projects and capable of firing a cluster of flechettes, an HE shell, or a variety of other lethal or non-lethal natures.

Looking even further ahead, perhaps someone will crack the energy supply problem and deliver an electromagnetic weapon capable of extremely high velocities at an acceptable size and weight.

Time will tell; but it could be very long time before we see the last of the 5.56x45 cartridge.

 

Service Cartridges

Metric Size mm

Bullet Weight g

Velocity m/s

Energy joules

6.5 Arisaka

6.5x50SR

9.0

762

2,600

7.92 Kurz

7.92x33

8.1

686

1,900

.30 Carbine

7.62x33

7.0

580

1,200

7.62 M1943

7.62x39

7.9

710

2,000

7.62 vz52

7.62x45

8.4

744

2,320

7mm Medium

7x49

9.0

790

2,800

5.45 AK 74

5.45x39

3.5

900

1,420

5.56 NATO

5.56x45

3.95

930

1,700

5.8 Chinese

5.8x42

4.15

930

1,800

7.62 NATO

7.62x51

9.33

838

3,275

 

Readers wishing to learn more about this subject will be interested in 'Assault Rifle: the Development of the Modern Military Rifle and its Ammunition' by Maxim Popenker and Anthony G Williams. Details are HERE

Sources:

Hogg, I and Weeks, J. Military Small Arms of the 20th century

Dugelby, T.B. Modern Military Bullpup Rifles

Long, D. Combat Rifles of the 21st Century

Stevens r. and Ezell, E. The SPIW: The Deadliest Weapon That Never Was

Huon, J. Military Rifle and Machine Gun Cartridges

Hogg, I. Jane's Directory of Military Small Arms Ammunition

Labbett, P. Assault Rifle Ammunition 5.6mm to 11mm Calibre

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