ASSAULT RIFLES AND THEIR AMMUNITION:

HISTORY AND PROSPECTS

Revised 22 June 2008

 

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 so 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.

Developments up to 1918

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 a Self-Loading Carbine in 7.65x32 calibre, an improved and enlarged version of their Model 1901 pistol carbine chambered for a lengthened version of the 7.65x25 pistol round, which was made in about 1904. It never went past the prototype stage and its ballistics are not known. However, the cartridge case is similar in length as well as calibre to the US .30 M1 Carbine's, but slightly fatter as it is bottle-necked.

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. It was originally chambered for Federov's own purpose-designed 6.5mm cartridge, but  as the Great War was then underway there was no chance of a new cartridge being adopted, so he modified his gun to use the Japanese 6.5x50SR Arisaka cartridge, large quantities of the guns and ammunition having been acquired by Russia to meet a shortfall in their supply of rifles. This was an excellent choice, as the cartridge combined moderate recoil with a good long-range performance, but only a few thousand Avtomats were made. They were used in action in the Russian Civil War (reportedly seeing action as late as the Winter War with Finland in 1939-40) and thereby earned their place in small-arms history.

It can be argued that neither the Cei-Rigotti nor the Federov Avtomat used "intermediate" cartridges, as the 6.5mm Carcano and Arisaka were the front-line rifle/MG rounds in the Italian and Japanese armies respectively. This is true, but it is worth bearing in mind that, in terms of calibre and muzzle energy, they were in the same class as the present-day 6.8x43 Remington SPC and 6.5x38 Grendel, which are today regarded by many as ideal cartridges for assault rifles.

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 the Model 1910 in .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. arguably the first purpose-designed intermediate military cartridge. The war ended before anything came of this, but it is not hard to see that had it lasted for another year or two, French troops would have been equipped with an assault rifle. As it was, neither the Ribeyrolle, nor a 7mm version designed in the 1920s, made further progress.

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 a semi-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.

The interwar period

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, especially Switzerland. Their prolific gun designer Furrer produced a short-recoil carbine with a new bottle-necked 7.65x35 cartridge in 1921. We are now getting very close to the concept except that the cartridge had a round-nosed rather than pointed bullet. A year later a modified 7.65x38 appeared which did have a pointed bullet. Swiss sources indicate that data from the tests of these rounds were passed to DWM in Germany, where they may have influenced later developments. Other pre-Second World War Swiss short-case ammunition designs included a different and rather mysterious 7.65x38 round for which unloaded components were made in some quantity, for an unknown destination, just before the war.

In the aftermath of the Great War a Hauptmann Piderit of the German Rifle Testing Commission advocated a short-cased cartridge and a suitable rifle to fire it, but his was a lone voice. It wasn't until 1927 that DWM (actually, the "Berlin-Karlsruher Industriewerke A.G." as DWM was known between 1922 and 1936) carried out the first tests of short-cased cartridges, possibly as a result of the data they had received about the Swiss rounds, but these had no direct result.

In 1925 Kynoch of the UK proposed a "7mm light automatic rifle cartridge" intended for BSA. The factory drawing shows a bottle-necked case with a length of 41mm and a round-nosed bullet. It is not clear whether the cartridge or gun were ever built.

In Russia, Federov continued to argue for the adoption of a smaller cartridge than the 7.62x54R. In the late 1920s he recommended adoption of the 6.5 mm calibre "if not even smaller" and a rimless or semi-rimmed case with a length shortened by about 20 % (to 40 mm). His ideas were supported in 1930 by V.E. Markevich, of the Red Army's Weapons Scientific and Research Range, who pointed out that an ideal cartridge already existed in the .25 Remington! The .25's bigger brother based on the same case, the .30 Remington, was of course used as the starting point for the development of the 6.8mm Rem SPC.

In the early 1930s Denmark made limited numbers of the delayed-blowback Weibel (or Danrif) assault rifle in a 7x44 calibre. Also in the early 1930s, the US Frankford Arsenal tested an Italian Terni semi-automatic rifle in 7.35x34, but nothing seems to have survived apart from a drawing of the round, which shows it with a pointed bullet of 8.7g. In 1939 a light automatic weapon was advertised in Greece in 7.92x36 calibre, the cartridge apparently being based on a shortened and necked-out 6.5mm Mannlicher case.

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 2,700J - much more powerful than the .25 Rem) most impressed the testers, but the Board chose the .276 Pedersen (7x51) a medium-power round developing 2,400J (similar in power to the 6.5mm Arisaka and to the modern 6.8mm Rem), which would have made an effective assault rifle cartridge. However, the army was still thinking in terms of long-range semi-automatic fire, a mindset which did not change until the 1960s. The .276 cartridge was rejected in 1932, partly for cost reasons but also because it did not offer sufficient long-range performance.

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

World War 2 and after - the Assault Rifle Emerges

In the run-up to World War 2, the focus switches to Germany.  Over a ten year period starting in the mid-1930s, no fewer than five German companies were involved in developing short-cased cartridges suitable for assault rifles: Geco, DWM, RWS, Rheinmetall-Borsig and Polte.

Geco was the first in the field, co-operating with the gun company Vollmer-Werke Maschinenfabrik, to produce the Vollmer SL Model 35 self-loading carbine in a nominal 7.75x40 calibre (the calibre was actually 7.9mm, with a bullet 8.05mm in diameter). This was officially tested with good results, but led to no orders. In 1942 Geco produced a new cartridge also intended for a Vollmer carbine, the 7x45SR. This used a wider case and was far more powerful, with a muzzle velocity of 1,000 m/s. Another cartridge, measuring 7.92x33.5, was designed at Geco and attributed to an H.G.Winter, a director of the firm, but the date and the gun for which it was intended are not known.

DWM designed a 7x39 cartridge in the mid-1930s, for which a Walther self-loading carbine was reportedly made. It was appreciably more powerful than the later 7.92x33 Kurz. However, the interest of the Heereswaffenamt (HWA) was by then focused on Polte developments, so the DWM round also failed to progress further. RWS produced several short-cased rifle rounds in the 1930s, including an 8x45, 8x46 and 7x46, but these developments were taken no further. Rheinmetall-Borsig were involved in a number of prewar experiments concerning 7mm rounds in various case lengths, some of them very long, probably for high-velocity aircraft gun projects. One drawing has been found of a 7x36 cartridge which would obviously have been suitable for assault rifles, but there is no evidence that it was made. The design work may have been done by Polte on behalf of Rheinmetall-Borsig.

This brings us to Polte Patronenfabrik of Magdeburg, who made by far the most significant contribution. The HWA awarded them a contract, probably in 1938, for the development of a short-cased infantry cartridge. This resulted in several different designs of cartridge; 7.9x45, 7.9x30, two different 7.9x33 and a 7x45, all by 1940. In all of these, Polte retained the head and rim diameters of the standard 7.92x57 rifle/MG round, and in all but the 7mm the same calibre as well. This kept production costs to a minimum and no doubt helped to account for the success of their proposals. The final 7.92x33 design (which had less case taper than the first or "transitional" effort) was approved in December 1940, the only subsequent change being to the angle of the extractor groove, which was altered from 45 to 60 degrees in May 1942.

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).

The author shooting the MKb42(W) at MoD Defence Academy The StG 44

 

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.

At the same time as the German work was reaching its conclusion, the USA was developing the .30 M1 Carbine, a light rifle chambered for a new 7.62x33 straight-cased round based on the .32 Winchester Special case. This was not intended as an assault rifle but as what would now be called a "personal defence weapon" for troops who would not normally carry a rifle. However, its handiness meant that some front-line troops carried it in preference to the much bigger and heavier .30 M1 Garand rifle. The M2 version of the Carbine introduced selective fire and was close to the specification of an assault rifle, but the cartridge with its round-nosed bullet was really too small and weak to reach out to 300m (330 yards), considered the desirable effective range as some 90% of fire-fights took place within that distance.

Attention now switches back to the USSR. The key date was 15th July 1943 when a meeting was held of the Technical Council of the People's Commissariat for Armament (NKV). They had met to consider "New foreign weapons firing lower-powered rounds" and studied examples of both the US .30 M1 Carbine supplied by the USA, and the German MKb 42 (H) in 7.92x33 which had been captured while undergoing troop trials. The meeting concluded that the new German gun and cartridge were important developments and decided that a new reduced-power round must be designed. Responsibility for this was handed over to the OKB-44 design bureau, which produced the first prototype of what became the 7.62mm M1943 round only a month later, with the first batch of ammunition loaded with flat-based lead-cored bullets being range-tested that December. This kept the same calibre as the 7.62x54R rifle/MG round for production convenience, but adopted a new case which was slimmer than that used by the 7.92x33. A pilot series-production run began in March 1944, and before the end of the war the round was combat-tested in prototypes of the Degtyarov RPD light machine gun and Simonov SKS semi-automatic carbine. At that time the case had a length of 41mm, but development work continued, resulting in a boat-tailed bullet shape being adopted and the lead core being replaced with mild steel. The case neck was reduced to the final 38.7mm to keep the overall round length the same despite the longer bullets.

The story was not yet over. Federov, the old pioneer and true father of the intermediate calibre selective fire rifle concept, now "Doctor of Services, Professor Lt. General (Technical Engineering Branch) V.G.Federov" and serving as a senior member of the Technical Council of the NKV, continued to argue for a smaller-calibre cartridge. As a result, between 1946 and 1948 several different rounds were made and tested in 6.75mm as well as 7.62mm calibre. Despite this, the 7.62x39 M1943 cartridge was finally selected in 1948, when the AK-47 was already undergoing pre-production troop trials. One of the reasons for retaining the 7.62mm calibre was said to be that the Soviet manufacturing plants did not at that time have the equipment to mass-produce smaller-calibre ammunition and gun barrels with the necessary precision.

Some sources claim that the 7.62x39 was no more than a copy of a German Geco cartridge for the Vollmer M 35 carbine, designed in 1934/35 by the aforementioned H.G.Winter. However, as we have seen, the cartridges designed for that gun were quite different, having larger case diameters. The round often cited as the model for the M1943 is the 7.62x38.5 "Mittelpatrone", but the diameter of that case is also larger than the M1943's and, according to Dynamit Nobel (Geco's postwar parent company), it dates from 1960; it appears that it was in fact inspired by the M1943, not the other way round. There is therefore no known German cartridge of which the 7.62x39 M1943 could have been a copy. The authors of a Russian history of the M1943, who had access to Soviet archives, were unable to find reliable information as to whether the USSR had any previous knowledge of the development of intermediate rounds in the West.

The next assault rifle to emerge after the StG 44 was the Kalashnikov AK (below), also chambered for the new  M1943 cartridge. 

 

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 were captured and examples would certainly have been provided to Soviet small-arms design teams) 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.

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). In 1959 the AK was replaced in production by the AKM, which was lighter and cheaper due to the replacement of the machined receiver by one of stamped steel. However, both AK and AKM have always been popularly if inaccurately known in the West as the AK-47.

The AK / AKM 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 EM-2 bullpup rifle, 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. There is some confusion over the EM-1, since two different weapons appear to have been assigned the same designation:  the first was a full-powered (7.92x57) bullpup gun by Roman Korsak, a Pole working in England, the second EM-1 was a rival to the EM-2 in the same 7x43 calibre, which had a similar bullpup configuration but was made from stampings and pressings rather than machined. Unlike the AK, which continued to be supplemented by the full-power 7.62x54R Nagant cartridge in MGs and sniper rifles, The EM-2 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.

The EM-2 + 7x43 combination appears to have achieved all that was asked of it, and in 1951 the cartridge was briefly adopted by the UK as the '7 mm Mk 1Z', at the same time as the EM-2 was adopted as the 'Rifle, No.9 Mk 1'. However, it faced insurmountable political obstacles. Previously, it had been submitted for comparative testing in the competition to select a new standard NATO rifle/MG cartridge. The 7x43 was regarded by the US Army's testers at Fort Benning as a better basis for development than the new US .30 cal round with which it was competing, 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. A change of government resulted in the British giving way and cancelling the EM-2 and its cartridge in favour of the FN FAL in 7.62x51 NATO, which apart from being half an inch shorter than the .30-06 cartridge represented no progress whatsoever over this fifty-year old design.

 

The EM-2 rifle (above)

TADEN GPMG (left) and 7.92mm EM-1 Roman Korsak LMG (below), which predated the 7x43 EM-1 and EM-2

 

 

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 AK74. 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. There is a small lead element at the back of the tip which moves forward on impact, causing the bullet to destabilise quickly. Despite this feature, it is understood that in some quarters the older M1943 round is still preferred.

More recently, the Chinese have ntroduced 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 is switching to 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. This issue is considered in more detail HERE.

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 (something which is not guaranteed with the SS109/M855 ammunition, even from rifle barrels). At lower velocities the bullets are even less likely to fragment and much of the wounding potential is lost. 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 were experimenting with a similar (and even bulkier) system, the PAPOP (below) with 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

What conclusions can we draw from all this?

One conclusion as a result of recent combat experience is that the performance of the small-calibre, high-velocity rounds (especially the 5.56mm NATO) is erratic; sometimes they work well, sometimes they don't, depending on their impact velocity, the precise manufacturing details and the angle at which they strike the target. There is more on the subject of small-arms terminal effectiveness HERE. These problems, combined with the poor barrier penetration of the SCHV rounds, have led to a revival of interest in 7.62x51 rifles, with manufacturers such as FN and HK offering 7.62mm versions of their new 5.56mm weapons (SCAR Heavy and HK417 respectively). 

While the US Army (the key to the introduction of any replacement cartridge) currently remains adamant in support of the 5.56mm, many observers feel that a more potent cartridge would provide much more reliable performance as well as better barrier penetration.

A larger-calibre, more powerful cartridge than the 5.56mm, but still generating light enough recoil to permit controllable automatic fire when required, might also deliver another side-benefit: its performance could be close enough to that of the 7.62mm NATO to permit the new cartridge to replace both existing 5.56mm and 7.62mm rounds, providing considerable benefits in the costs of small-arms acquisition, training and support. This would incidentally make the term "assault rifle" obsolete, as such a common-calibre gun would simply be the standard infantry rifle.  In fact, this is arguably the case already, as there seems little point in maintaining the distinction between full-power "battle rifles" and intermediate power "assault rifles" when these can just be basically the same weapon in different calibres.

 Is it possible to achieve a suitable common cartridge? 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 middle option, the 6.5mm. A cartridge of this performance could be smaller in length and diameter than the old military 6.5mm rifle rounds such as the Arisaka, the Carcano and the Mannlicher, with a diameter of around 10.5mm and a length of about 45mm. In fact, the case diameter and length would be similar for all of the cartridges in the list above.

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 diameter of 10.5mm, intermediate between the 5.56x45 (9.5mm) and the 7.62x51 (12.0mm). Overall length is kept within the 57mm limit to fit in the M16 action, which limits the length of the bullets which can be loaded. Even so, 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 11.3mm 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.

The designs of both the 6.8mm Rem and the 6.5mm Grendel have been compromised by the need to keep within the 57mm overall length of the 5.56x45, so that existing 5.56mm weapons can be rebarrelled to chamber them. A clean-sheet design would probably result in an overall length of around 65mm.

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.

- and the Future?

Attention is now focusing on the next generation of infantry small arms, for 2020 and beyond. The British Army has already determined that the SA80 family will serve until that date and has started a project to consider its replacement, but given the planning time involved it is inevitable that the new weapons will be bought more or less off-the-shelf and will be chambered for existing service ammunition.

As far as the USA is concerned, it now seems unlikely that a conventional replacement for the 5.56mm and 7.62mm cartridges will ever be selected. The argument will always be that any benefits from a new round will be reduced by disadvantages (e.g. greater bulk, weight and recoil than the 5.56mm), so that the changeover would not be worth the huge cost. This means that a more radical approach would be needed, to provide some substantial advantages - but what? 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 technology is being revived, along with plastic-cased telescoped rounds.

The US Army is funding the 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. AAI Corporation is the lead contractor for the project and is responsible for the gun design. Two different cartridge designs are being tested, shown below in comparison with existing rounds. One is a polymer-cased telescoped round (by ARES), the other a caseless round (by ATK) based on HK G11 technology. The linked polymer-cased rounds are showing a 35% reduction in weight over conventional 5.56x45 ammunition, the caseless rounds a 50% weight reduction plus a 40% reduction in bulk. The preferred solution is the caseless round because of the greater reductions, with the plastic-cased round as a fall-back in case the caseless one meets with insuperable technical obstacles. The plastic-cased round is perceived as a lower risk and has currently made more progress, the gun having been extensively tested. If this project results in a service weapon, the earliest in-service date could be 2015.

A dummy AAI LSAT LMG is shown below. On the right is the belt of plastic-cased ammunition, with a sectioned dummy caseless round resting on the belt to show the size comparison

The initial calibre and ballistics have been chosen to match the 5.56x45 SS109/M855 for comparison purposes, but in parallel with this, consideration is being given to 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, which implies a calibre somewhere in the region of 6.5mm as discussed above. If so, the possibilities of building a new assault rifle round this "intermediate" MG round are obvious, and AAI is already considering this.

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 less-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 a long time before we see the last of the 5.56x45 cartridge.

Current service rifle/MG rounds and potential developments, from left to right: 7.62x54R, 7.62x39, 5.45x39, 7.62x51, 5.56x45, 5.8x42, 6.8x43 Rem SPC, 6.5x38 Grendel, earlier versions of LSAT caseless and LSAT plastic-cased.

 

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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