ASSAULT RIFLES AND THEIR AMMUNITION:

HISTORY AND PROSPECTS

© Anthony G Williams

Amended November 2012

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 standard 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. machine pistols and 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, the 7.62x54R 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 rifle fire from the shoulder. 

Pistols such as the Mauser C96 (7.63x25) and P08 Luger (9x19 Parabellum) produced carbine derivatives with detachable stocks, usually only capable of semi-automatic fire but a few with a burst-fire option. 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 in service (if you discount the curious twin-barrel Villar Perosa) was the Bergman MP18 in 9x19, which was the ancestor of the MP 38/40, the Sten Gun, the PPSh and so on. An honourable mention also to the Thompson, developed separately in the USA from 1916 onwards for their .45 Auto cartridge. An oddity was the Pedersen Device of 1918, which replaced the bolt in the US Springfield Rifle with a semi-automatic mechanism to fire small .30 cal (7.62x20) pistol-type rounds developing less than 400 joules; it was never used in anger.

Attempts to improve the power and range of the SMGs, such as the development of the .45 Remington-Thomson in the experimental Model 1923 Thompson SMG (which used a very powerful loading developing almost three times the muzzle energy of the .45 Auto) and the use of the 9x25 Mauser round in the 1930s Solothurn S1-100 and Hungarian Kiraly 39M and 43M SMGs (which saw some service), did not catch on. There is a limit to the degree to which the performance of such weapons can be increased as their large-calibre, relatively light and round-nosed bullets lose velocity quickly. Also, the basic API blowback system used by most SMGs is not suited to high-powered ammunition, although the Kiraly and Thompson M1923 had more sophisticated mechanisms.

More recently, small-calibre high-velocity PDW ammunition has emerged (described in more detail in THIS article).  The FN 5.7x28 has achieved some sales, in both the Five-seveN pistol and the P90 SMG, as has the rival HK 4.6x30 in the MP7. However, despite their improved range performance, these cartridges only develop around 500 joules so don't qualify as assault rifle ammunition. The  Chinese 5.8x21 DAP-92 is even less powerful.

Above: .30 Pedersen (7.65x20), .30 Mauser (7.63x25), 9x19 Parabellum, 9x25 Mauser, .45 Auto, .45 Remington-Thompson, 5.7x28 FN, 4.6x30 HK, 5.8x21 DAP-92

Although a self-loading rifle did not enter general service as a standard infantry rifle until the US M1 Garand became available in 1937, there were many earlier models, some of which are shown on the left. However, attempts to make such weapons fully automatic ran into difficulties due to the power of their cartridges. Perhaps the most famous example was  the German FG 42 paratroop rifle in 7.9x57. Some of the early rifles in 7.62x51 NATO, such as the American M14, German G3 and some versions of the FN FAL, 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. The most successful attempt at this was probably the Swiss Stg.57 in 7.5x55 but this was significantly heavier than contemporary rifles, the weight helping to absorb the recoil. The American Browning Automatic Rifle (BAR) in .30'06 was very controllable but this was even heavier, weighing about twice as much as a "standard military rifle", so is excluded by the definition.

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. 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 7.5-8mm 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).

Above: some early semi-automatic rifles, from top to bottom: 1918 .303 Farquhar Hill; 1909 Mondragon (7.92mm); 1917 MAT Mk 1917; 1929 Czech Brno Z.H.29 (photo taken at MoD Defence Academy, Shrivenham)

 

FCAR rounds score well in the traditional methods of measuring barrier penetration and terminal effectiveness (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. 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 barrier penetration may be reduced and stopping power becomes more controversial (relying on velocity and rapid bullet yaw on impact rather than calibre and bullet mass; which according to combat reports sometimes works, sometimes doesn't). The long-range performance also begins to decrease 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.

Right: the full-power 7.9x57, 7.5x55, .30-06 and 7.62x51, shown next to the 7.62x39 and 5.56x45 which illustrate the most common FCAR and RCAR rounds respectively

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 7.63x25 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.

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 high-velocity 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 and also as late as the Winter War with Finland in 1939-40, and thereby earned their place in small-arms history.

6.5x52 Italian, 6.5x50SR Japanese Type 30, 7.65x32 Mannlicher, .351 Winchester SL, 8mm Ribeyrolle (replica)

Federov Avtomat 8mm Ribeyrolle

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 intermediate 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 rifle bullet, creating the 8mm Ribeyrolle – arguably the first purpose-designed intermediate military cartridge. This was tested in July 1918 and found to be effective out to 400m. 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 could have been equipped with an assault rifle. As it was, neither the Ribeyrolle, nor a 7mm version designed in the 1920s, made further progress.

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 Fürrer 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 used much later 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) M/32 assault rifle in a 7x44 calibre. From this rifle, the 8 gram (123 grain) bullet reportedly achieved a muzzle velocity of 750 m/sec (2,460 fps) for a muzzle energy of 1,653 ft-lbs. 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.

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 began 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. This happened for several reasons. One was that long-range MG fire was considered essential: the first Japanese Army 7.7mm round was only available in MGs (the first 7.7mm rifles only emerging about a decade later), and other powerful MG rounds (e.g. the 8mm Breda, 8mm Bofors and 8mm Solothurn) were introduced during this period.

For the most part, the introduction of rifles in the new MG calibres seems to have been to simplify ammunition supply arrangements, rather than because the smaller calibre rifles were felt to be ineffective.

The Italian 7.35mm was a special case: they were aiming for a pointed-bullet loading of the 6.5x52 but increased the calibre because it was cheaper to rebore existing worn-out barrels instead of buying new ones.

Finally, the need for a full-auto rifle (and therefore lower-powered ammunition with less recoil) was not recognised and probably 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.

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 .256 (6.5mm), a .276 and the existing .30. The .256 (8g at 820 m/s, for 2,700J - much more powerful than the .25 Remington) 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, the later 7x43 British and the modern 6.8mm Remington), 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.

Swiss 7.65x35, Swiss 7.65x38 with bullet alongside, .276 Pedersen, 7.35x52 Italian

World War 2 to 1960 - 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 7.9x33.5, 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 7.9x33 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 base diameter of the standard 7.9x57 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 7.9x33 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, with nearly half a million made. 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 old .32 Winchester SL commercial 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 7.9x33 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 (left), 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 7.62x38, the French 7.65mm Model 48 (7.92x35 - the French also experimented with calibres up to 9mm) and the 7.5x43 CRBA of the late 1950s, the Danish 7x36 Madsen or Otterup and the unusual Spanish 7.92x40 CETME Model 53 (which used a lightweight but highly streamlined bullet to achieve good long-range performance with light recoil, also tried in other calibres) were all unsuccessful contenders during the 1950s. Falling loosely into this category were the late-WW2 efforts in Finland, producing such cartridges as the bottlenecked 9x35 Lahti (in the AL43 - a modified SMG design) and the straight-cased 9x40 Lilja, but these had light, round-nosed bullets indicating their SMG point of origin. A 7.62x35 version of the Lahti, with a pointed bullet, was more promising but still not adopted.

WW2 and after: .30 M1 Carbine, 9x35 Lahti, 9x40 Lilja, 7.92x33 Kurz, 7.62x39 AK, 7.5x45 Czech, 7.62x45 Czech, 7x36 Madsen/Otterup, 7.65x38 French,7.5x43 French CRBA, 7.62x38 Swiss, 7.92x40 CETME

Another which very nearly saw service was the British EM-2 bullpup rifle, initially chambered for a new .280 cartridge (later with a slightly modified rim as the .280/30 - both measured 7x43 in metric terms) which after experiments with 8.4g (130 grain) bullets was trialled with a 9.0g (140 grain) bullet at 736 m/s (2,415 fps), for a muzzle energy of 2,440 joules. 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 Sten SMG and the full-power .303 Lee Enfield 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 (at least partly) the Vickers MMG.

The EM-2 was submitted for comparative testing in the competition to select a new standard NATO rifle/MG cartridge. The result was promising: 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, who both made ammunition) 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, by carrying out a lot of work to improve its performance. The first effort was to step up the velocity to 770 m/s (2,525 fps), followed by seating the bullet less deeply to make more room for propellant (the 7mm Optimum or 'S'). Longer cases were also tried: a UK-only High Velocity variant with a 49.5mm case length and a velocity of about 838 m/s (2,750 fps); then the 7mm Compromise (the new US .30 cal case necked-down, with a length of 51mm) with a muzzle velocity of about 850 m/s 2,800 fps); then the 7mm Second Optimum or Medium (the Belgian 7x49 with an MV of 840 m/s (which was the only one of the series to see service - with Venezuela in the FN FAL rifle). In all of these, the bullet remained the same weight at 9.0g.

The EM-2 + 7x43 combination appears to have achieved all that was asked of it, and in 1951, while the above experiments were going on, the cartridge was briefly adopted by the UK as the '7 mm Mk 1Z' (with the 43mm case length and a 9.0g bullet at 777 m/s - 140 grains at 2,550 fps), at the same time as the EM-2 was adopted as the 'Rifle, No.9 Mk 1'. However, it faced insurmountable political obstacles. 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 was reworked to fire the new NATO round, but the heavy recoil destroyed the balance of the weapon and it went no further.

.30-06,  .30 T65 (7.62x48), .280/30 (7x43), 7x49 Medium, 7x51 Compromise, 7.62x51

A couple of other peripheral issues are worth mentioning. An early in-house rival to the .280 was the .270 (6.8x46) which used a more slender case of similar base diameter to the .276 Pedersen, the 7.62x39 and the present-day 6.5mm Grendel and 7x46 UIAC. This was optimised for shorter ranges so fired a light, 6.48g (100 grain) bullet at 840 m/s (2,750 fps). This was not good enough at long range, but the cartridge clearly had the potential to fire a heavier bullet at a still respectable velocity. It would arguably have made a better basis for a general-purpose round than the .280, which was biased in favour of very long-range performance to meet US requirements. It is also worth noting that there is some confusion over the EM-1, since two different weapons were 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 with a different action and was made from stampings and pressings rather than machined. 

The EM-2 rifle (above left and right)

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

The Small Calibre High Velocity (SCHV) Revolution

Small-calibre rifle cartridges were in use or under development for military purposes from very early days. 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. At that time the available propellants were not suited to getting the best from such rounds.

American experiments were made in the 1950s with a range of smaller calibres, such as the .22 APG (designed for use in a modified M2 Carbine), .22/30 NATO, the .25/30 NATO (6.35x51) and the .27 NATO (6.85x51), but these led to nothing.

 

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

SCHV rounds:   .22 APG, .22/30 Homologous (5.56x51), .25/30 Homologous (6.35x51), .27/30 Homologous (6.86x51), .224 Winchester E2, .25 Win FA-T 116 (6.35x48), .25 Win Duplex FA-T 127 (6.35x53), 5.56x45 M855, 5.45x39 AK74, 5.8x42 Chinese

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 7.62mm M14 rifle (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 (after some competition from the .224 Winchester and two different .25" Winchesters (6.35x48 and 6.35x53). The 5.56 was 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. The USA has continued to develop improved 5.56mm ammunition, recently adopting the lead-free M855A1 Enhanced Performance Round and (for the USMC) the MK318 Mod 0.

Rather surprisingly, the Russians were inspired by the 5.56mm to develop a new 5.45x39 7N6 cartridge for their next-generation rifle, the AK74. This is a bit less powerful than the 5.56 NATO although the bullet does have an exceptionally good aerodynamic form achieved partly by a hollow tip, giving it a good performance at long range. 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 7.62mm M1943 round is still preferred.

More recently, the Chinese have introduced a 5.8x42 calibre for assault rifles and LMGs. The ballistics seem little different from the 5.56mm, although it is claimed that it outperforms it, 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. The  most recent development is the introduction of a new, universal loading of this cartridge (designated DPB-10), intended to replace the earlier versions. This has a 4.6g bullet at 915 m/s  for (71 grains at 3,000 fps).

The SPIW

At one time great hopes were placed in 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 1,200-1,500 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 which began in the late 1950s, in which several manufacturers produced weapons using basically similar ammunition firing a 1.8mm diameter dart with a plastic "puller" sabot filling the case mouth. The cartridge cases went through various evolutions (some of them shown here) and AAI's XM645 included primer-actuated unlocking: a large piston primer was designed to be moved backwards by the chamber pressure (an idea previously used in US experiments in the 1930s).

All manner of rifles from several manufacturers were developed to fire this ammunition, varying from traditional-looking wood-stocked ones, bullpups, space-age designs and even multi-barrel guns, some with drum magazines. Accuracy was not as good as conventional rifles, however, and the cost of the ammunition was very high. Doubts were also raised about the terminal effectiveness against unprotected targets (penetration of armour was excellent). Attempting to achieve everything in one weapon by building in a multi-shot grenade launcher didn't help.

The SPIW project faded out, eventually closing down in the early 1970s and leaving the "temporary" 5.56x45 with the accidental prize of becoming the USA's, and subsequently NATO's, new rifle/LMG calibre.

 There were also several attempts at a multi-flechette weapon; one example being the .330" Amron Aerojet, another being the 9.53x76R, both of which contained three flechettes within their light-alloy cases.

Experimental US flechette rounds: 5.56x45 for scale, sectioned 5.6x44 XM216,  XM216 (Springfield/Frankford, second generation), 5.6x44 XM144 (Springfield/Frankford, first generation), 5.6x53B XM110 (AAI first generation), 5.6x57B XM645 (AAI second generation) - all part of the SPIW programme; .330 Amron Aerojet, 9.53x76R (both multiple flechettes)

More Conventional 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. Germany produced an interesting-looking 6.5x43 round in the early 1960s, but only for ballistic testing.

Perhaps the most interesting and instructive series of experiments took place in the UK in the late 1960s, when a 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 (100 grains at 2,680 fps), 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 longer and slimmer case would have been adopted. Tests revealed that the 6.25mm cartridge matched the 7.62mm 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 (aluminium 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.

Some experiments since the 1970s: 5.56x45 for scale, 6.5x43 German, 6.25x43 British, 6x45 SAW, 6x50 SAW aluminium-cased, 6.45x48 Swiss GP80

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 12mm-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.

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 (Frankford Arsenal/Ballistic Research Laboratories), which combined a light-alloy case with a lightweight but aerodynamic bullet 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

Exotica

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. 7.62mm APDS loadings have also been tried, and one of them has seen service with the Swedish Army as a sniper round.

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

Special loadings of service rounds: 7.62x51 M198 Duplex, .30'06 triplex, 7.62x51 salvo-squeezebore, 7.62x51 SLAP (Saboted Light Armor Penetrator) APDS

The closest to adoption of all of the exotics was the caseless cartridge, in the form of the Heckler & Koch G11 rifle. 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 temporarily fell into the hands of Royal Ordnance, where they 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 in various calibres but these are no longer offered.

Caseless ammunition has obvious benefits. It is much lighter and more compact (no metal case plus compressed propellant), 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 ammunition in sealed plastic see-through packs which clipped directly to the gun), sealing the breech against gas escape is more difficult, and the propellant is more likely to "cook-off" in a hot chamber; a problem exacerbated by the fact that a brass cartridge case transports some heat from the gun. Despite this, H&K (or rather Dynamit Nobel) developed a new heat-resistant kind of propellant, although at great cost. The current effort to use exotic technologies, the US Army's LSAT programme (described below), has explored caseless ammunition based on Dynamit Nobel's work, but is finding plastic-cased ammunition easier to work with.

The ACR programme

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, and H&K submitted the caseless G11 described above, while AAI and Steyr 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, so this once again proved a dead end.

 

The four ACR contenders shown above: HK G11 (foreground), Steyr (top left), Colt (upper right), AAI (middle right)

The ACR rounds: Colt 5.56mm Duplex, AAI 5.56mm flechette, Steyr flechette, HK 4.7mm G11

The four ACR contenders shown above: Colt (top left), AAI (top right) Steyr (above right), HK G11 (above left). Photos taken at MoD Defence Academy, Shrivenham

The HK G11 had a rather complex mechanism.....

The current arsenal

 

Despite all of these experiments, small arms currently in service are relatively conventional, at least as far as the assault rifle element is concerned. With the break-up of the Warsaw Pact, several East European nations have switched to 5.56mm NATO weapons, either bought-in or of their own design. Even Russia is now offering Kalashnikovs for export sale in 5.56x45 as well as its domestic calibres.

The US Army has switched to the M4, a carbine version of the M16 with a shorter barrel.  Current (2012) US plans consist of two parallel programmes: a product-improved M4 in competition with a separate contest for a new carbine, which will inevitably be in 5.56x45 calibre. 

 

The US Special Operations Command (SOCOM) selected the FN SCAR rifle/carbine in Light (MK16 in 5.56x45) and Heavy (MK17 in 7.62x51) versions, although they are currently focusing just on the MK17. Heckler & Koch has achieved sales success with the G36 (above) and now also offers paired 5.56mm and 7.62mm weapons, the HK416 and HK417 respectively, as does Colt with its CM901 which can be converted from one calibre to the other. The photo on the right shows the HK416 at the top, the HK417 at the bottom and the experimental HK416/6.8mm in the middle. Several other countries have also been developing new 5.56mm rifles, notably Beretta in Italy with the ARX-160, plus Poland and the Czech Republic, and others in Asia and the Americas.

All these weapons use a traditional instead of bullpup layout, in contrast to the Chinese QBZ-95, the Israeli Tavor (below right), the SAR-21 from Singapore (below left) the FN2000 (bottom left), and the first 5.56mm bullpup to enter service, the Steyr AUG, which is still offered in updated form. All of these weapons except for the 5.8mm QBZ-95 are chambered for the usual 5.56x45 NATO.

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 much shorter barrel for the same overall length. 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 yaw on impact 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 has restarted this argument, with the terminal effectiveness of the 5.56x45 becoming controversial once again. The pros and cons of the bullpup vs traditional layout are explored HERE.

The Lessons

What conclusions can we draw from all this?

One conclusion as a result of recent combat experience is that the 5.56mm weapons are most effective in short-range combat. That was satisfactory in Iraq which mainly saw urban fighting, but was revealed as a major deficiency in the much longer ranges common in Afghanistan. The British and US Armies both found that the 300-400m maximum effective range of 5.56mm weapons was inadequate when foot patrols were engaged by small groups of Taleban, using 7.62x54R SVD rifles and PKM LMGs at ranges of up to 900m. As a result, 7.62mm rifles and MGs have made a comeback at section level in the foot patrols.

In addition, 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. The 7.62mm weapons are more reliably effective but are much heavier (both guns and ammunition), and the recoil of the rifles is also heavy, making automatic fire uncontrollable.

A larger-calibre, more powerful cartridge than the 5.56mm, but still significantly lighter than 7.62mm and generating light enough recoil to permit controllable automatic rifle fire when required, might also deliver another substantial 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 reducing the weight of MG ammunition plus the costs of small-arms acquisition, training and support. The August 2011 report by the US Army's PEO Soldier report titled Soldier Battlefield Effectiveness includes a number of points in favour of general-purpose weapons and ammunition, summarised concisely in this:

"Ultimately, Army service rifles must be general purpose in nature and embody a series of tradeoffs that balance optimum performance for a wide range of possible missions in a range of operating environments. With global missions taking Soldiers from islands to mountains and jungles to deserts, the Army can’t buy 1.1 million new service rifles every time it’s called upon to operate in a different environment."

Is it possible to achieve a suitable general-purpose cartridge? The evidence suggests strongly that it is. A 2010 investigation into rifle calibres by the US Army's ARDEC compared cartridges in 5.56mm, 6mm, 6.35mm, 6.8mm and 7.62mm calibres and determined that, when considered across a range of criteria, the 6.8mm offered the best compromise with the 6.35mm following closely behind, both of these being clearly ahead of the others. In 2012 the US Army's Marksmanship unit (AMU) carried out its own investigations into the optimum cartridge for future military rifles and concluded in favour of 6.5mm.

The British aimed for this with the 7x43 cartridge half a century ago, and by all accounts succeeded admirably. This gives us an upper calibre limit. It seems unlikely that a cartridge with the long-range performance to replace the 7.62mm can be achieved with anything smaller than 6.5mm calibre, which gives us the lower limit. We need to specify a bullet sectional density ratio of at least .230 and preferably .250 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. This works out as the following range of choices with minimum bullet weights in common calibres:

7mm/.276": bullet weight 8.4-9 g (130-140 grains) at 772-745 m/s (2,532-2,440 fps) = 2,500J

6.86mm/.270": bullet weight 7.9-8.5 g (124-131 grains) at 788-760 m/s (2,585-2,500 fps) = 2,455J

6.5mm/.258": bullet weight 7.25-8 g (112-122 grains) at 820-780 m/s (2,690-2,560 fps) = 2,430J

Any of the above options would do, but for the sake of argument let's take 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 10.6mm 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. As a matter of interest, the four standard case diameters manufactured in the West and adopted by most cartridges in this class are approximately 9.6mm (5.56 NATO), 10.6mm (6.8mm Remington), 11.3mm (6.5mm Grendel), and 12.0mm (7.62mm NATO).

Long after writing this section, I discovered an old scrap of paper on which I had jotted down a proposed "General Purpose Cartridge" in 1971. At that time I was a youngster who knew nothing of the 6mm SAW or 6.25mm British experiments which were then underway, but my proposal was remarkably similar to the conclusions I reached in writing this article: a 6.5x45 GPC with a body diameter of about 10.5mm and an overall length of 65mm, firing a 120 grain bullet at 2,600 fps. I quote this not in order to demonstrate my precocious prescience, but to illustrate that the characteristics of the optimum compromise cartridge are quite obvious to anyone who takes a passing interest in the subject. For anyone interested, the paper is HERE.

One important point which needs to borne in mind, however, is the current trend towards using lead-free ammunition. Bullets with cores of copper or steel need to be longer than lead-cored bullets of the same weight, and since low-drag 6.5mm bullets are rather long anyway, making them lead-free could cause technical problems - especially given the need for even longer tracer bullets. This suggests a larger calibre might be preferable, possibly 6.86mm.

7.62x51 and 5.56x45 rounds are on the left, next to photographic mock-ups showing three possible options for a general-purpose cartridge: the 6.5x45, 6.8x45 and 7x45. These were created by slightly extending the 6.8x43 Rem case and pasting on bullets of appropriate calibres

The current contenders

So, we have our ideal military general-purpose assault rifle and MG cartridge - 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); not too different from the 'ideal' 6.86mm listed above. The cartridge case is based on the old .30 Remington commercial round, with a diameter of 10.6mm, intermediate between the 5.56x45 (9.5mm) and the 7.62x51 (11.9mm). 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, blunting their long-range performance. 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, although not adopted for logistic and financial reasons. SOCOM, and now the USMC, has instead adopted the 5.56mm MK318 Mod 0 SOST ammunition, which is reportedly much more effective but uses an open-point bullet unacceptable to UK and probably other European countries. In any case, while the 6.8mm Remington would be a significant improvement over the 5.56mm, it does not have the range to replace 7.62mm and thus could not be a general-purpose cartridge.

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. This clearly has potential for a general-purpose cartridge, but there are some reservations. The performance shown below is achieved with a high-quality target bullet; a military ball round with a crimping cannelure would not have such a good ballistic coefficient. Also, adopting a lead-free design would significantly lengthen the bullet (and a tracer even more so) so it would have to protrude more deeply into the case, reducing the propellant capacity. And the shape of the case may be rather stubby to be ideal in a belt-fed MG.

The photo shows the 5.56x45 M855A1,  6.5x38 Grendel, 6.8x43 Remington SPC and 7.62x51 M80, with their bullets. Note the bullets beside the 5.56mm: the new M855A1 (with an exposed steel tip) has the lead core element replaced by copper, resulting in a significant increase in length to achieve the same weight as the SS109 next to it. The other bullets are all lead-cored; note the much more aerodynamic proportions of the 6.5mm compared with the others (especially the rather stubby 6.8mm)

The graph above shows the bullet energies at ranges of 100 to 1,000 metres for the four cartridges mentioned. The differences between the 5.56 mm, 6.8 mm and 7.62 mm are gradually magnified as the range increases, with the 6.8 mm producing 1.5x the energy of the 5.56 mm at 100 m, but 2.1x at 1,000 m, while the 7.62 mm develops 2x of the 5.56 mm's energy at 100 m and 3.4x at 1,000 m. The more aerodynamic bullet of the 6.5 mm Grendel means that its initial advantage of 1.6x of the 5.56 mm's energy at 100 m increases dramatically to 3.8x at 1,000 m – greater even than the 7.62 mm M80.

The designs of both the 6.8mm Remington 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.

Another new round currently being developed by Cris Murray, who was involved in the 6.8mm Remington development, is the 7x46 UIAC (Universal Intermediate Assault Cartridge). This is based on the same 11.3mm case diameter as the 6.5mm Grendel. In its proposed standard loading it fires a 130 grain bullet at 2,650 fps (8.4g at 810 m/s). This develops 2,750 J, so it is very much at the top end of the size, calibre and power range. The extra case width over the 6.8mm Rem's 10.6mm might however prove useful in accommodating long, lead-free bullets and possibly thicker cases made from polymer, should these succeed in meeting military requirements. Interestingly, the basic case dimensions of the UIAC are very similar to those of the .270 British from the late 1940s, and the performance is very similar to that of the .276 Pedersen of the late 1920s.

Of the current rounds, the 7mm UIAC and the 6.5mm Grendel represent the top and bottom of the range for a general-purpose rifle/MG round in terms of their performance,  recoil, calibre, size and weight. Perhaps the ideal lies somewhere in between?

The photo on the left shows the .276 Pedersen, .270 British, 7x43 British, 7.62x51 NATO, 7x46 UIAC, and 6.5x38 Grendel

Lightweight Small Arms Technologies Programme (LSAT)

The US Army has for several years been funding the Lightweight Small Arms Technologies ( LSAT ) development programme, with the aim of halving the weight of the current 5.56 mm M249 (FN Minimi) LMG and its ammunition. The AAI Corporation is the lead contractor for the project and is responsible for the gun design. Two different cartridge designs have been tested, shown below in comparison with existing rounds. One is a polymer-cased telescoped round (by ARES) now in "Spiral 3"  - the third generation, the other a caseless round (by ATK) based on HK G11 technology. The caseless rounds save 38% in volume, and weigh 6.3g each compared with c.12.2g for the M855 to give overall weight savings of 51% (due to the lighter plastic belt links). The plastic-cased Spiral 3 rounds are 40mm long by 11.4mm in diameter and save just 13% in volume, and weigh 8.3g. They save 41% in weight in MG belts compared with M855 belts, due to the plastic links which weigh 0.5g compared with 2.0g for the steel links. Total weight of a 200-round belt of Spiral 3 ammunition is 1.76kg compared with 2.84kg for M855. 

The emphasis has been on developing LMGs to date, but there is also a programme to develop a carbine to use the same ammunition. The first SN1 model (a mock-up of which is shown below) was test-fired in May 2010 and has been tested at TRL 5. This used an interesting mechanism which withdraws the rounds backwards from the magazine, resulting in a longer barrel length for a given overall length: the saving in length is about 100mm compared with 200mm achieved by a bullpup layout. A second model of carbine (SN2) was being prepared for firing tests in mid-2011, with the aim of offering M16 performance at M4 weight and length.

While the caseless ammunition is both lighter and more compact than the plastic-cased, the usual technical problems experienced with such ammunition has led to the emphasis being placed on the latter. By mid-2011 some 400 caseless rounds had been fired with a TRL 5 demonstration planned for the autumn. In contrast, some 14,000 plastic-cased rounds had been fired through four LMGs, and eight LMGs plus 100,000 rounds of plastic-cased ammunition (loaded with M855A1 bullets) were supplied to the US Army for initial testing in autumn 2011. Initial informal reports indicate that this seems to have gone well, but the cost of establishing new production facilities for both guns and ammunition will clearly be a major obstacle to adoption. The funding for the project is now closing down and it seems that any service weapon is seen as a long-term possibility, for 2020+.

The initial calibre and ballistics of LSAT 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 develop an intermediate calibre cartridge which might replace both the 5.56mm and the 7.62mm. And the suggested characteristics of this new cartridge? 6.5mm calibre, firing a 120 grain bullet which matches the effectiveness of the 7.62x51 at 1,000m. This is beginning to sound familiar...

Above: the LSAT LMG

Below: the LSAT family: caseless above left, plastic-cased-telescoped Spiral 1 (top right), Spiral 2 (centre) and Spiral 3

Above: a dummy of the first LSAT carbine.

Below: a belt of 5.56x45 is shown next to LSAT belts: caseless (centre) and plastic-cased Spiral 3. Plastic belt links help to save weight.

Future Options

In the near term, 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 at least that date (although the weapons are wearing out in the trying conditions of Afghanistan) and has started a project to consider its replacement, but given the planning time involved it is almost certain that the new weapons will be bought more or less off-the-shelf and will be chambered for existing service ammunition. However, any further delays might bring LSAT into the frame, if it is adopted by the USA. Even if LSAT fails, a second opportunity will arise in the late 2020s when the existing 5.56mm and 7.62mm machine guns will be coming up for replacement. One standard LMG to replace both existing weapons, in a calibre capable of reaching out effectively as far as 7.62mm while saving a lot of gun and ammunition weight, would prove highly attractive. A rifle could then be developed to use the same ammunition. It would therefore be helpful for the new British rifle to be of the modular type, capable of changing between calibres via a conversion kit.

The key to all of this is of course the USA, since it is unlikely that any NATO nation will adopt a new rifle/MG cartridge unless the USA does so first. At the moment, the only new cartridge on the horizon is the LSAT. If this fails, any new conventional cartridge would have an uphill battle to achieve acceptance since 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 the changeover would not be worth the huge cost. A counter-argument to this lies not just with the weight savings over the 7.62mm, but also the development of computerised rifle sights such as the US DInGO which will enable ordinary riflemen to accurately engage targets out to the sort of ranges currently reserved for snipers - provided the gun and ammunition are capable of such ranges.

If LSAT is not accepted, a possible alternative would be an otherwise conventional but polymer-cased round (with a metal base insert). These have been tried before and failed, but the US firm PCP is using new technology which it claims will meet military requirements for heavy use in MGs. Weight savings won't be quite as spectacular as with LSAT, but they will still be well worth having.

Within the foreseeable future the current metal-cased ammunition may therefore be replaced by something a lot lighter and possibly more compact. If that happens, let's hope that the military takes the opportunity to adopt something like the "optimum compromise" discussed above. Until then, we're almost certainly stuck with the 5.56mm, supplemented by 7.62mm weapons where extra range or hitting power are required.

Taking all of this into account, there would appear to be good reasons to devote modest resources to developing a general-purpose round using conventional ammunition technology. This would have two purposes:

1. To establish the optimum calibre, ballistics and bullet design; data which can be fed into LSAT or any other advanced-technology project.

2. If advanced-technology ammunition proves unacceptable, it would be ready to be adopted as the next NATO round, with the possible later option of a polymer case..

It would be a tragically wasted opportunity if the next generation of NATO small-arms is designed around the 5.56mm and 7.62mm, just because that's what we have, when we know that we could do much better.

Service Cartridges

Metric Size mm

Bullet Weight g

Velocity m/s

Energy joules

6.5 Arisaka (Type 38)

6.5x50SR

9.0 (pointed)

762

2,600

6.5 Carcano 6.5x52 10.5 700 2,570
7.35 Carcano 7.35x51 8.4 756 2,400

7.9 Kurz

7.9x33

8.1

686

1,900

.30 Carbine

7.62x33

7.0

580

1,200

7.62 M1943 AK

7.62x39

7.9

710

2,000

7.62 vz52

7.62x45

8.4

744

2,320

7mm Medium

7x49

9.0

840

3,175

5.45 AK 74

5.45x39

3.5

900

1,420

5.56 NATO

5.56x45

3.95

930

1,700

5.8 Chinese (DPB 10)

5.8x42

4.6

915

1,925

7.62 NATO

7.62x51

9.33

838

3,275

7.62 M1891 Mosin Nagant 7.62x54R 9.75 835 3,400

 

From left to right: .276 Enfield 1910 (7x60); 6.5mm Arisaka Type 38 (6.5x50SR); .276 Pedersen (7x51); .270 British (6.8x46); .280/30 British (7x43); 6.25mm British prototype (6.25x43); 6.25mm British proposed (6.25x46); 6mm SAW (6x45); 7.62mm NATO (7.62x51); 5.56mm NATO (5.56x45); 6.8mm Remington SPC (6.8x43); 6.5mm Grendel (6.5x38); 7mm UIAC (7x46); 7.62mm M1891 Mosin Nagant (7.62x54R); 7.62mm M1943 AK (7.62x39); 5.45mm AK74 (5.45x39); 5.8mm Chinese (5.8x42).

 

A more detailed examination of the case for a new intermediate rifle/MG round is HERE

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

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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