By Anthony G. Williams

Today there are only six cartridges used in rifle-calibre machine guns in the world’s major armies: the 7.62x54R Russian, 7.62×51 NATO, 7.62×39 Russian, 5.45×39 Russian, 5.56×45 NATO and 5.8×42 Chinese. Of these, only the first two are traditional “full power” rounds, a type which until World War II was used in almost all rifles and machine guns. Yet during the 20th century many different full-power rifle-calibre cartridges were developed and used in machine guns, and this article describes the ones which saw significant military service.

The definition of “machine gun” can be stretched to include the Gatling and other manually operated repeaters that were developed during and after the period of the American Civil War. However, this article will be focusing on the small-calibre high-velocity rounds that entered service in recoil or gas-operated machine guns from the last decade or so of the 19th century. The first of these guns was the famous Maxim which was first adopted by Italy and Austria in 1887, used by many nations, and redesigned and improved in the UK (Vickers), Germany (MG 14 Parabellum), Russia and Switzerland. The Maxim was offered in a wide range of calibres to suit the national preferences of its purchasers, as were other widely popular machine guns such as the Madsen (from 1902), Schwarzlose (1905) and the interwar FN-built Brownings. Other much-exported guns, particularly the Hotchkiss models (the first of which was adopted in 1897), were more often sold in their original calibres.

It is worth noting that a few of the older manually-operated guns were adapted to use the modern smaller-calibre ammunition. Conversely, some of the older black-powder rounds were updated with smokeless powder, chambered in modern MGs and remained in use until after World War I. These included the French 11x59R Gras rifle cartridge, which was loaded with incendiary bullets and chambered in Hotchkiss and Vickers MGs for shooting at hydrogen-filled observation balloons and airships during the Great War. The British Royal Navy also retained Maxim machine guns in a cordite-loaded version of the .45 inch Gardner-Gatling calibre until after that war.

These were rare exceptions. By the beginning of the Great War, most major armies had switched to using the new small-calibre rifle rounds in automatic machine guns. These mainly fell into two groups: 7-8mm and 6-6.5mm calibre. Those developed in the 19th century and the very beginning of the 20th were initially loaded with heavy round-nosed bullets, after which lighter spitzer (pointed) bullets, fired at higher muzzle velocities, were introduced. Most of the earlier cartridges were then modified to use spitzer bullets (in some cases the opportunity was taken to alter the cartridge dimensions as well), but a few retained only round-nosed bullets until the end of their service lives, the best-known of these being the Italian 6.5mm Carcano.

Of the 6-6.5mm group, the US Navy’s 6mm Lee had the smallest calibre to see service until the 1960s, although the cartridge case was relatively large. It dates back to 1895 and was really ahead of its time, as propellants available then could not extract the potential of the cartridge, which developed a muzzle energy of less than 1,650 ft/lbs. The only MG chambered for it was Browning’s first service design, the Colt Mk 1 (also known as the M1895 and, more popularly, the “potato digger”), and the cartridge was replaced twelve years later by the US Army’s .30-06 round. The other rounds in this group were all of 6.5mm calibre and broadly comparable in size and power; the Japanese 6.5x50SR Arisaka (round-nosed Type 30 adopted in 1897, Type 38 spitzer loading in 1905), Italian 6.5×52 Carcano (1891), Dutch/Romanian 6.5x54R Mannlicher (1892), Greek 6.5×54 Mannlicher-Schönauer (1903) and Swedish 6.5×55 Mauser (1894 – also used by Norway, Denmark and Luxembourg). All of these developed around 1,800-2,100 ft/lbs muzzle energy. Of these, the 6.5×55 was the biggest, most powerful and most long-lived, and remains a popular round for commercial hunting rifles.

The larger calibre group showed a little more variety in performance, typically developing muzzle energies in the 2,200-3,000 ft/lbs range in the later spitzer loadings. The dominant rounds throughout this period were the German 7.92×57 first developed in 1888 as the Patrone 88/8, although modified to take a spitzer bullet (S-Patrone) of slightly larger diameter in 1905, the British .303 inch (7.7x56R) of 1889 (the round-nosed bullet replaced by the Mk VII spitzer ball in 1910), the Russian 7.62x54R of 1891 (spitzer loading in 1908), and the American .30-06 (7.62×63) of 1906. The spitzer-bullet .30-06 replaced the slightly longer .30-03 (7.62×65 with a round-nosed bullet) of 1903 which had in turn replaced the .30-40 Krag (7.62x59R) of 1892. Of these, the 7.92mm Mauser and the .303 were used by many nations prior to and during World War 2, the .303 even by Italy and Japan as a consequence of interwar exports of Vickers and Lewis aircraft MGs. The 7.62x54R of course remains in front-line military service in Russia, China and many other countries to this day, while the 7.92×57 and.30-06 cartridges are very popular in hunting rifles. These were supplemented by many other cartridges, however: it appeared to be fashionable for each nation which could afford it to have its own unique rifle/MG round. In addition, some “rifle calibre” rounds were specifically developed for machine guns.

The French 8x50R Lebel was actually the first modern smokeless-powder round to be adopted, with the flat-nosed Balle M bullet in 1886, and in 1898 also introduced the first military spitzer loading, the famous solid brass Balle D, which was also the first to have a boat tail. It was replaced in service by the short-lived 7.5×58 in 1924 before that was in turn replaced by the slightly modified 7.5×54 Model 1929 five years later, to reduce any confusion between the 7.5×58 and the 7.92×57. The new cartridge was, however, very similar to the Swiss 7.5×55 adopted in 1911 with a boat-tailed spitzer bullet to replace the earlier round-nosed 7.5×53 of 1889. The 7.5×54 remained in French service until replaced by the 7.62×51 in the 1970s, while the 7.5×55 is still in Swiss service and is available in military and hunting loadings.

The German-developed 7×57 Mauser, a slightly necked-down version of the older 7.92×57, saw service with Spain from 1892, several South American nations and Serbia, in various different machine guns. The 7mm remains a deservedly popular commercial hunting cartridge, being regarded as one of the most useful rounds for anything short of heavy and dangerous game. Another popular military cartridge was the 7.65×53 Mauser of 1889, also known by the names of the principal user countries as the Belgian, Argentine and Turkish Mausers: in addition it was used by some other South American countries. A spitzer bullet loading was not adopted until the 1920s. Despite this widespread military use it has never achieved much popularity as a commercial hunting round.

Other rifle rounds to see service in machine guns include the 8x50R Mannlicher first adopted by the Austro-Hungarian Empire in 1886 (and subsequently used by Bulgaria), the 8x52R Siamese Mauser of 1923, and the 8x58R Krag-Jorgensen of 1889 (spitzer bullet loading 1908) used by Denmark, Sweden and Norway.

Several nations decided to upgrade the performance of their machine guns by adopting new rounds specifically for them. Most such changes were made in the interwar period, although the Dutch had used their unique 7.92x57R as a special-purpose machine gun round since 1908. The Japanese first adopted the 7.7x58SR in its Type 89 version (in 1929), later replaced by a modified loading, the Type 92: later still came the rimless 7.7×58 Type 99, used in rifles as well as MGs. Norway adopted the 7.92×61 in 1929, Austria, Hungary and Bulgaria the 8x56R Solothurn from 1930 (unusual at that late date for using a rimmed case), Sweden the 8×63 in 1932, and Italy the 8×59 Breda in 1935. In some cases rifles chambered for these rounds were also made, but with the main exception of the 7.7mm Type 99 these were primarily to provide MG troops with commonality of ammunition. In addition, in 1938 the Italians adopted the Breda M38 in their new 7.35×51 rifle cartridge (the 6.5×52 Carcano necked-up to accept a larger, spitzer, bullet), but before the change to the new calibre had made much progress, the Second World War broke out and caused the changeover to be stopped.

The end of the Second World War saw most of these old calibres gradually phased out, although some lingered for a few decades. New “intermediate” cartridges primarily intended for selective-fire assault rifles were developed, and these were soon used in light machine guns. The two remaining full-power rounds, the old 7.62x54R Russian and the 1950s 7.62×51 NATO, are still extensively used in GPMGs and specialist rifles and look as if they will continue in those roles for a long time to come. Nearly all of the rest have either vanished into history or, in a few cases, are surviving by virtue of their popularity in hunting rifles.

(This article is based on excerpts from the book “Machine Gun: the Development of the Machine Gun from the 19th Century to the Present Day”, by Maxim Popenker and Anthony G Williams, published by The Crowood Press (UK) in July 2008. Anthony G Williams is Co-editor of Jane’s Ammunition Handbook and his website is at www.quarry.nildram.co.uk.)

By Anthony G. Williams

The Great War of 1914-1918 saw the first substantial use of aircraft in a major conflict. At the beginning the aircraft were almost all frail, underpowered devices that could barely lift themselves and their one or two crew into the air, and carried no armament except for the crew’s personal weapons. By the end of the conflict, heavy bombers carrying multiple defensive machine guns contested the air with fast and agile fighters, typically armed with two fixed machine guns synchronised to fire through the propeller blades. As well as ball rounds these guns fired a variety of specially developed ammunition, loaded with armour-piercing, incendiary and even explosive bullets.

Although machine guns specially designed for the needs of air fighting were being developed at the end of the war, none of these had time to get into service. So with the exception of a few large-calibre cannon, the air war was fought with more or less modified versions of the guns used on the ground by the army.

The Austro-Hungarian Empire, with its capital in Vienna, was one of the major combatants in the Great War, fighting alongside Germany and the Ottoman Empire against France, the United Kingdom, Russia (until 1917), Italy (from 1915, initially only against the Austro-Hungarian Empire), and the USA (from 1917). Defeat in the war led to the break-up of both the Austro-Hungarian and Ottoman Empires.

The standard machine gun of the Austro-Hungarian armed forces was the Schwarzlose. This was designed by a German, Andreas Wilhelm Schwarzlose, who took out the first patent in 1902. It was adopted by the Empire in 1905 as the M05 (Model 1905) and manufactured at the Osterreichische Waffenfabrik Gessellschaft in Steyr, Austria. An improved model, the M07, replaced the M05 two years later, to be replaced in production by the further-modified M07/12 five years after that. However, the older versions remained in service.

The Schwarzlose was unusual by comparison with the common locked breech short-recoil (e.g. Maxim) and gas-operated (e.g. Hotchkiss and Lewis) guns in that its mechanism used a form of blowback, in which the gas pressure in the barrel forces the cartridge case backwards, pushing the unlocked bolt to the rear of the gun. In its simplest form, the blowback mechanism is restricted to very low-powered cartridges because it is necessary for the inertia of the bolt to hold the case in the chamber until the projectile has left the barrel, otherwise high-velocity burning gas will burst from the breech to the discomfiture of the firer. With high-pressure military rifle cartridges, the weight of bolt required would be so heavy that the rate of fire would be very low.

Various solutions to this difficulty have been tried, because blowback weapons are attractively simple and cheap to manufacture. One is the retarded blowback, in which an additional mechanism resists the initial rearward movement of the bolt, and this was the approach adopted by Schwarzlose. His design utilises an elbow joint attached to the bolt by one arm with the other arm pivoted to a fixed axis on the receiver. The effect of this mechanism is to force the initial rearward movement to operate under severe mechanical disadvantage, delaying the opening of the breech until the bullet has left the barrel. Even so, the cartridges it used were so powerful that the breech still opened too quickly. The solution was to shorten the barrel to 20 inches (compared with 28 inches for the Maxim) so that the bullet left the muzzle sooner before the breech could open. It was belt-fed, using a fabric belt. The simplicity of the mechanism kept the cost down to about half that of a Maxim, and the gun was subsequently adopted by several other European countries in a variety of different calibres. The ruggedness and reliability of the Schwarzlose made it a popular gun and it had a long life, though the main problem being the sensitivity of the mechanism to ammunition quality. The Dutch were still making it in 1940, and it was being used at least until 1945 as a second-line weapon in Italy and Hungary.

In army and naval use, the gun is recognisable by the short and wide water-filled barrel jacket, the large conical flash-hider attached to the muzzle (the short barrel presumably resulting in a much bigger muzzle flash than usual) and the curved shape of the back of the receiver. As with all blowback guns there is no primary extraction, so the gun was fitted with an oil tank and the chamber was sprayed with oil before each round was chambered in order to facilitate case extraction. This mechanism was the source of some discomfort in aircraft use when Schwarzloses were mounted in front of the pilot, as he received a constant spray of oil in his face whenever the guns were fired. In at least one installation – in the Albatross fighter – a metal shield and drainage tube were fitted to catch and dispose the oil.

The cartridge in use in the Austro-Hungarian Empire was the 8x50R Mannlicher, developed in 1886 by the Georg Roth ammunition factory of Vienna together with the Vienna Armory, and one of the first of the small-calibre military rounds designed to use the new smokeless powder. The US equivalent was the .30-40 Krag of 1892. The initial loading featured a heavy (244-grain) round-nosed bullet fired at 2,030 fps, although some later specialised loadings, such as the M.08 armour-piercing and the M.17 and M.18 incendiary types, used pointed bullets. There was also an explosive bullet with a blunt nose and a waisted body. These explosive and incendiary types were intended for use against hydrogen-filled observation balloons, initially from ground-fired guns and later from aircraft.

The Schwarzlose as an Aircraft Gun

The Schwarzlose was not an obvious choice for an aircraft gun, being bulky, heavy (at around 43 pounds) and initially slow-firing at around 400 rpm (500 rpm for the M07/12). However, except for a few imported Madsens, Bergmanns and LMG 08/15s, it was all the Austro-Hungarians had available so it was adapted for the task. At the start of the conflict the Empire also pressed into aerial service some Schwarzlose M12s intended for export to Greece, chambered for their 6.5×54 Mannlicher-Schönauer cartridge. This fired a 160-grain round-nosed bullet at 2,230 fps. The M12 guns were lighter, being air-cooled, and were used as flexibly-mounted defensive weapons, but the small bullet was less effective so these were eventually replaced by 8mm guns.

The first change to the gun for aircraft use was the removal of the flash hider. The next concerned the water jacket. Cooling water was not necessary for an aircraft gun: the combination of short bursts of fire and a strong wind keeping the barrel cool enough. So the jacket was frequently emptied of water and fitted with large slots to allow air to circulate. Unlike the Vickers/Maxim short-recoil guns in which the front of the barrel jacket was needed to support the moving barrel, the only other function of the jacket in the fixed-barrel Schwarzlose was to hold the foresight. Once separate sights were used, the jacket could be dispensed with entirely, leaving the plain, skinny barrel protruding rather oddly from the bulky receiver. Despite these modifications, some Schwarzloses fitted to aircraft retained their cooling water jackets to the end of the war.

The M07/12 was found to be sensitive to changes in atmospheric pressure, firing more slowly and finally stopping when the aircraft climbed above an altitude of 10,000 feet. A set of modifications designed by Ludwing Kral raised the rate of fire to nearly 600 rpm and the critical altitude to almost 18,000 feet. Mid-way through the war, a version specifically for aircraft use was developed, the M16, in which the weight was reduced to 29 pounds. Continued development eventually saw the free rate of fire of the M16A increased to 880 rpm, and raised its operating altitude to 23,000 feet. But even in March 1918 fewer than 300 M16s were in service, and the M07/12 remained numerically the most important gun in the inventory.

By the middle of the war, it had become established that the most satisfactory layout for a fighter plane was the tractor type, with the engine in front of the pilot. This meant that if the guns were to be kept within reach of the pilot (important at that time, as guns often jammed and needed clearing), their firing needed to be synchronised with the engine revolutions so that the bullets passed between the propeller blades.

Most synchronisation systems needed to be tailored to the gun they were used with, and the Schwarzlose’s unique mechanism required a purpose-designed system. The most common seems to have been the Zaparka gear, which fired the gun on every fourth propeller revolution. The mechanism could be relied on only within a band of engine revolutions between 1,000 and 1,600 rpm with the M07/12, and 600 to 1,600 rpm with the M16. This explains the very prominent place given in the cockpit of fighters to a large engine tachometer. The 1,600 revolutions per minute limit restricted the maximum rate of fire to 400 rpm regardless of the free rate, and it would obviously have been less at lower engine revolutions. The Bernatzik and Daimler gear reduced the rate of fire even more, by 55% in the case of the M16. However, the Daimler gear did have the advantage that the M16 could be safely fired from engine idle to 1,600 revolutions per minute, although the M07/12 was still restricted to the 1,100 to 1,600 rpm band. None of these systems proved to be entirely reliable, leading to a loss of confidence in the pilots who risked shooting off their own propellers. At the end of the war the Austro-Hungarian forces decided to standardize on the Priesel system.

Aircraft installations

Aircraft used by the Austro-Hungarian Empire were a mixture of indigenous and German types. Some of the latter were specifically made for the Empire, and these were usually armed with Schwarzlose guns.

Synchronisation systems for the Schwarzlose were not available until 1916, so earlier fighters needed to find other ways to mount their guns. Among the first of the Empire’s fighters was the German-built Hansa-Brandenburg D.I, armed with an unsynchronised Schwarzlose in a fairing on top of the upper wing so it could fire over the propeller. This fairing was known as the VK canister. The standard version was the Type II VK, which held a gun and 250 rounds of ammunition, plus a gravity fuel tank, but sometimes two guns were installed in the canister. The Hansa-Brandenburg D.I was also built under licence by the Austro-Hungarian Phönix company, but this version did not prove very successful. The Phönix D.I combined its fuselage with new wings, a more powerful engine, and two synchronised Schwarzlose guns. It was a much better fighter, but deliveries started only in the spring of 1918. Very small numbers were delivered of the improved D.II and D.III. After the war, the D.III went on to serve with the Swedish Air Force. The other successful family of Austro-Hungarian fighters was entirely indigenous. The Österreich-Ungarische Aviatik Flugzeugfabrik (not to be confused with the German Automobil und Aviatik A.G., which also built a number of fighters) produced the Aviatik D.I, which in prototype form had a single synchronised Schwarzlose but entered service in the summer of 1917 with two.

In addition to these, the German Albatros D.II and D.III fighters were built in the Empire and armed with two synchronised Schwarzloses. Some Fokker D and E series were also used.

Despite its bulk, the Schwarzlose was also used as a defensive gun in flexible mountings. Single-engined two-seaters (known as the C class in both Germany and the Empire) which carried such armament included the German-built Hansa-Brandenburg C.1 (which also had a fixed gun in a VK top-wing canister for the pilot) and several indigenous designs from Lloyd, Lohner, Oeffag and Phönix. Thirty twin-engined German Gotha bombers were supplied to Austria, who fitted them with Schwarzlose MGs. Hansa-Brandenburg also supplied the W.18 floatplane, and the indigenous Lohner L of 1915 was a three-seat single-engined flying boat. Both carried one Schwarzlose gun.

While the Schwarzlose was not best suited to aircraft use, the Austro-Hungarian Empire engineers were able to make some remarkable improvements, which turned it into an acceptable aircraft gun.

Schwarzlose Technical Data

Length: ….. 42 inches Barrel length: ….. 20.9 inches Weight: ….. 43 lbs (M05, M07, M07/12), 29 lbs (M12, M16) Method of operation: ….. Retarded blowback Calibre: ….. 8x50R Mannlicher (except M12: 6.5×54 Mannlicher-Schönauer) Ammunition feed: ….. Cloth belt Cyclic rate of fire: ….. c.400 rpm (M05, M07, M12), c.500-580 rpm (M07/12), c.600 rpm (M16), c.880 rpm (M16A)

(Anthony G Williams is co-author (with Emmanuel Gustin) of “Flying Guns – World War 1: Development of Aircraft Guns, Ammunition and Installations 1914-32”, published by The Crowood Press in 2003. You can visit him at www.quarry.nildram.co.uk)

There have been relatively few attempts to introduce new heavy machine gun cartridges since the end of the Second World War. The main reason for this is that many of the roles formerly carried out by these guns have been taken over by cannon of 20mm or larger calibre, while their remaining tasks can be adequately carried out by the existing rounds. However, that has not stopped several manufacturers from experimenting, usually with new technology which possesses some theoretical advantages. The first two considered here are, however, conventional: the BRG rounds from Fabrique Nationale of Herstal, Belgium.

15×115 FN

Having observed that armoured personnel carriers and other light AFVs were acquiring thicker armour as protection against .50/12.7mm AP rounds, FN decided to develop a more powerful HMG to give NATO an equivalent to the Russian 14.5mm KPV. The gun, designated the BRG-15, was a gasoperated, dual-feed design, and it was first chambered for a cartridge made by necking down the 20×110 Hispano case to create the 15×115. However, this experienced difficulties with barrel wear and inaccuracy, so it was decided to replace the cartridge with a new design; the 15.5x 106.

15.5×106 FN

For the new BRG-15 cartridge it was decided to abandon the conventional jacketed bullet design and replace it with slightly larger-calibre projectiles using a cannonstyle separate driving (rotating) band made of plastic. It was also decided to adopt an entirely new case, this time based on theRussian 14.5×114. This is wider than the Hispano case, so it was possible to shorten it while still retaining the same ballistics, resulting in the 15.5×106. Despite all of this work, the project was shelved in 1991.

Several attempts have been made to simplify ammunition and gun design in the postwar period. These have included various shapes of caseless rounds, and “folded” cartridges with the bullet alongside the propellant. Three of the more practical efforts are described below.

.50 Dardick Tround

This system was developed by David Dardick in the 1950s, and was aimed at simplifying the gun feeding mechanism. The basic idea was to push the cartridges sideways into an open chamber instead of lengthwise into a closed one. Three of these chambers were formed on the outside of a revolving cylinder; at any given moment, one round was being loaded, the second fired and the third ejected. The cylinder was partly surrounded by a fixed sleeve; this left two chambers open for loading and ejection, but supported the round being fired by providing the third side of the chamber.

This would not have worked with a conventional cartridge case, so each round was entirely surrounded by a plastic case with three slightly rounded sides. This not only provided a close fit with the supporting chamber walls, but also added strength to make up for the lack of a solid chamber. The description “triangular round” was shortened to Tround.

Most of the initial effort was in small arms with a few examples being made for commercial sale, but these were not successful and production stopped in the 1960s. However, interest in larger-calibre automatic versions continued, mainly because the short cartridge movements involved in chambering and ejection permit a very smooth action with an extremely high rate of fire. Experiments with a .50 calibre Tround MG continued into the 1990s, but did not result in a production gun.

.50 Hughes Lockless

A different approach to the same problem was tried by Hughes in the 1970s. They also developed a gun with a sideways-loading chamber, although in this case the chamber was fixed while the surrounding sleeve moved. The ammunition was in the form of a flat box, which was slotted into the chamber from the side; the shape led it to be dubbed the “chiclet”. Before firing, the loading and ejection ports were covered by a sliding sleeve to complete the chamber. The next round to be c h a m b e r e d pushed the fired case out of the ejection port. This layout led to a very simple gun mechanism, and ammunition was made in calibres from 5.56mm to 30mm, but again without any production being achieved.

The cartridge is interesting because it is of the “telescoped” type; the propellant is packed around the bullet instead of behind it, leading to a much shorter cartridge. Ignition takes place in two stages. The primer first ignites a small quantity of propellant; just enough to drive the bullet up into the bore and thereby seal the chamber. The movement of the bullet exposes holes connecting with the main body of the propellant, which then ignites to drive the bullet from the barrel. The expansion space left by the bullet on its initial movement means thatthe propellant can be packed in tightly, allowing the case to be very compact.

.50 ARES TARG

This was another telescoped round, although with a more conventional cylindrical shape and designed for a very different type of gun action. The TARG (Telescoped Automatic Revolver Gun) was of the conventional single-barrel revolving cylinder type, as the name suggests. The cylinder had four chambers and, as with the Hughes Lockless, ejection occurred when the next round to be chambered pushed the fired case out of the chamber. The project commenced in 1989 and resulted in a light and compact machine gun, but it was cancelled in the late 1990s when ARES was acquired by the AAI Corporation.

In HMGs, as with small arms, much work on producing designs to use advanced ammunition concepts has failed to result in any production contracts. However, it seems unlikely that this will always be the case. The US Army is experimenting once more with telescoped ammunition (both plastic cased and caseless) in the Lightweight Small Arms Technologies (LSAT) programme, while the British and French are bidding to introduce 40mm cased telescoped ammunition in the CTWS (Cased Telescoped Weapon System) for future use in light armoured fighting vehicles. We have not yet reached the end of the development of the heavy machine gun cartridge.