Steam Chests

A few posts ago, when we studied heavy machine guns, it was mentioned that one of the features of some of these machine guns is a jacket filled with water, which surrounds the barrel and helps to prevent it from overheating.

Of course, if several rounds were to be fired rapidly, the intense heat of the barrel would cause the water to turn into steam and evaporate, thereby reducing the cooling effectiveness of the jacket. In the early Maxim heavy machine guns, the users would simply unscrew a cap on the top of the water jacket and refill it with more water, whenever the water level in the jacket got low.

A Maxim machine gun. Click on the image to enlarge.

Image licensed under the Creative Commons Attribution-Share Alike 3.0 License by Jonathan Cardy at Wikipedia

However, this presented a logistical problem to its users because then they needed to position the heavy machine gun next to a supply of water and this was not always possible in the battlefield. Resourceful users found that they could urinate into the water jacket in an emergency, but it is not possible to do that on demand, therefore it is preferable that a reliable supply of water be nearby. Another problem was that the steam rising from the barrel could also give away the position of the machine gun. This was a problem in trenches and rough terrain, since heavy machine guns cannot be moved as quickly by troops without a vehicle. Another issue was that if the steam was not allowed to escape out of the water jacket, the steam pressure inside could build up to the point of rupturing the jacket.

To counter these issues, newer models of heavy machine guns at the end of World War I were issued with steam chests. A steam chest, or more properly, a steam condensing chest, is simply a container that is placed below the barrel and is connected to the water jacket via a short pipe (or pipes). When steam is created by the hot barrel, instead of allowing the steam to escape out of the water jacket, it is transported through the pipe into the steam chest, where it condenses back into water. Periodically, this water is poured back into the water jacket for reuse. This system allows users to conserve their water supply for much longer and also prevents steam from rising and revealing their position to enemies.

A Browing M1917A1 machine gun. Note the steam chest attached to the front of the water jacket.

In the above image, we see a Browning M1917A1 machine gun. The steam condensing chest is the rectangular can at the front with the rubber hose coming out of it. The steam coming out of the water jacket flows through the rubber tube (which has some water in it as well) and into the rectangular can, where it cools down enough to become water again. Periodically, the crew lifts the can above the height of the water jacket, which causes the water in the can to flow back through the tube into the water jacket.

In the above image, note that the can is a custom made device with its own folding carrying handle. However, any convenient container could be used as well, as the image below shows:

A British Vickers machine gun with its condensing chest. Click on the image to enlarge. Public domain image.

In the above example, we see a Vickers machine gun, as used by the British military. The steam chest on the right of the picture has some faint lettering on it, which may be discerned by clicking on the image to enlarge it. Still having trouble reading the letters?? The image below shows a closeup of the steam chest with the letters clearly visible:

A can of Shell gasoline! Public domain image. Click on the image to enlarge.

Yes, that is a can originally meant to hold gasoline (or petrol, for non-American readers), made by Shell, the well known oil company. These cans were issued to British troops as standard equipment with Vickers machine guns, to be used as steam chests!

In more advanced models, the steam chest was equipped with a manual pump, which allowed the users to pump the water back into the water jacket without moving the steam chest.

A Colt MG 38 machine gun. Click on the image to enlarge.

In the above image, we see a Colt MG 38 machine gun with its steam chest positioned at the left of the image. Note that there are two pipes coming out of the water jacket into the steam chest. The pipe on the right of the picture transports the steam out of the water jacket into the steam chest and the other pipe sends water back from the chest into the water jacket. Also note that the steam chest has a handle to the left of it. The user turns this handle, which operates the manual pump inside the steam chest and sends water back into the water jacket. With this design, the user does not need to lift the can to pour the water back.

It must be noted that steam chest systems aren't air-tight, so a little steam does always escape out. However, they allow their crews to re-use their water for a lot longer.

Steam chests were supplied with most heavy machine gun models made in between World Wars I and II. As water-cooled heavy machine guns began to be phased out of military inventories and replaced with air-cooled models, the need for steam chests went away as well. With the invention of improved metallurgical techniques for making barrels last longer at higher temperatures, as well as the development of quick-change barrels, the extra weight of the water jacket, water and the steam chest were simply not worth the trouble for most users. That is why no modern machine guns use steam chests any more.

General Purpose Machine Guns

In our last couple of posts, we looked at medium machine guns. In today's post, we will look at some developments in the General Purpose Machine Gun (GPMG) category (otherwise called Universal Machine Gun or UMG).

A general purpose machine gun is a weapon designed to use both magazines and belt feed, firing full sized rifle-cartridges, which is air-cooled and designed to be used either as an infantry support weapon (i.e. like a light machine gun), or as a vehicle mounted weapon (i.e. like a medium machine gun). Since it is air-cooled, a GPMG usually features quick-change barrels, so it can continue to fire on automatic mode for longer periods of time. A general purpose machine gun can be mounted on a bipod or a tripod, or even from a vehicle, such as a jeep or a helicopter.

The first GPMGs were something we'd just studied in the previous post. The MG 34 was the first general purpose machine gun. Carried by an infantry man with a drum magazine and mounted on a bipod, it served as a great infantry support weapon used for offensive operations. By switching the magazine with an ammunition belt and mounting it on a tripod, it became a very good medium machine gun. Mounted on a tank or a vehicle, it was an effective anti-aircraft and defensive machine gun.

Public domain image of a MG 34 machine gun. Click on the image to enlarge

The only problem with the MG 34 was that it was somewhat harder to manufacture, due to the fact that it needed some precision machining. Due to this, the Germans came out with the MG-42, which was easier to manufacture, more reliable, and as an extra bonus, had a higher rate of fire as well!

A MG-42 mouinted on a tripod. Click on the image to enlarge. Public domain image.

The MG-42 design was extremely successful and some variants (such as the MG3 and MG74 models) are still in service in some militaries around the world. It also influenced other countries to manufacture their own GPMGs based somewhat on the MG-42 design.

The US military was one of the first to pick up the idea of a GPMG from the Germans and started working on a design in the late 1940s. One of the requirements was that this gun had to be chambered to fire 7.62x51 mm. NATO ammunition and another requirement was that it should be capable of being fired accurately from the shoulder as well. After a number of trials, the final design was approved in 1957 and was called the M60 machine gun. The M60 served in various branches of the US military during the Vietnam war. It was carried by infantry units as a Squad Automatic Weapon (SAW) to support infantry operations and was also mounted on river patrol boats (PBRs), M113 Armored Personnel Carriers (APC) and as a door gun on helicopters.

US Marines with a M60 in Vietnam. Public domain image.

While the M60 saw service in Vietnam, some design flaws became obvious. For one, it had some jamming issues in muddy and humid conditions. It did better when used in static-defense or helicopter mounted roles, because it could be stored in cleaner conditions and regularly maintained. One more problem was the design of the barrel, which had a permanently attached bipod and this made barrel changes more difficult and took longer to accomplish. While some improvements to the design were made, the US military rejected the M60E3 and went with the Belgian FN MAG (which we will study in a second) and designated it as the M240 in US service.

Around the time that the US was developing the M60, the Fabrique Nationale company (FN) of Belgium was also developing their own GPMG, which they called the FN MAG (the letters MAG stood for Mitralleuse d'Appui Generale, which is French for "General Purpose Machine Gun"). Like the M60, the FN MAG is also designed to fire 7.62x51 mm. NATO cartridges. While it is heavier than the M60 and uses a more complicated gas operated system, it is more reliable compared to the M60. This is why it was also adopted by the US military as the M240 to replace the M60s in service. The M240 was first mounted on to tanks in 1977 and later adopted by other US military branches during the 1980s and 1990s.

US Marines firing a M240G mounted on a tripod. Click on the image to enlarge. Public domain image.

The FN MAG and the M240 continue to be used in service in many military forces around the world.

Other GPMGs include the Soviet PK series, the Heckler & Koch HK 21 etc.

Medium Machine Guns - II

In our last post, we looked at the early beginnings of medium machine guns. We will continue to study this class of machine gun in this post.

Before World War II, the German military came to the conclusion that static warfare tactics from World War I were obsolete and began to train using maneuver warfare concepts. Therefore, they needed a machine gun that could have a high rate of fire, but could be transported reasonably easily by hand, as well as used from a mobile platform. It was decided to design an air-cooled weapon with interchangeable barrels, so that it could fire rapidly for longer periods. The result was the MG 34 machine gun.

MG 34 Machine Gun. Click on the image to enlarge. Public domain image.

The MG 34 was used with great success by the German military in the early stages of World War II, but the rate of manufacture was slow because it needed some very precise machining to make it. Therefore, the German military held a new design contest for an improved machine gun and the result was the MG 42 machine gun.

Interestingly, the winning design was submitted by a company with no previous experience in firearms manufacturing, but they had experience in mass production technologies and knew how to produce stamped machine parts (they made metal lanterns!) The lead designer, Dr. Werner Gruner, actually attended a military machine gunner's course to familiarize himself with machine guns and talked to soldiers about what they wanted to see in a weapon. The resulting MG 42 design was much easier and faster to produce than the MG 34. It also had a much higher rate of fire (1200 to 1500 rounds/minute) than any other machine gun of that era. 

MG 42 on a tripod. Click on the image to enlarge. Public domain image.

Like the MG 34, the MG 42 could be carried by a single user and operated with a bipod in a light machine gun role. It could also be mounted on a tripod (such as in the image above) and used by a team in a medium machine gun role. When used in a medium machine gun role, the optimum team size was six: a commander who directed the team, a no. 1 gunner who carried the gun and fired it, a no. 2 gunner to carry the tripod (which weighed about twice as much as the gun!) and three others to carry spare barrels, ammunition, entrenching tools etc. The first three team members also carried pistols for protection, while the other three carried rifles. Often, the team consisted of only three members though, a gunner, loader and spotter.

The MG 42 was a very influential design and some variants continue to be used by military forces even in the present day. It also influenced other designs, such as the US M60 machine gun, the German MG 3 etc.

In our next couple of posts, we will study how the medium machine gun transitioned into the General Purpose Machine Gun class and the development of Squad Automatic Weapons (SAW)

Medium Machine Guns - I

In our last few posts, we looked at light machine guns and heavy machine guns. Briefly, a light machine gun fires intermediate-sized ammunition, comes with a bipod, operated by a single user and is generally carried by and used to support infantry. A heavy machine gun fires larger-than-ordinary rifle cartridges, is mounted on a vehicle or a tripod, sometimes operated by a team of people and is used against troops, light armor, buildings, low flying aircraft etc. In today's post, we will study another class of machine guns, the medium machine gun, otherwise called the MMG.

A medium machine gun is a weapon that fires full-sized rifle cartridges in automatic mode. They are generally air-cooled and belt fed. They also weigh somewhere in between the weight of a light machine gun and a heavy machine gun. Typical weight for a MMG is somewhere between 25 lbs. and 40 lbs. (or 11.34 kg. to 18.14 kg.) They began to emerge towards the end of World War I, as a balance between light machine guns and heavy machine guns. Recall that in World War I, light machine guns were made to be fed by smaller box magazines and fired in bursts only. Medium machine guns were designed to be fired on automatic for much longer, but without the heavy water cooling mechanism, weight or recoil of a heavy machine gun. Therefore, a medium machine gun offered flexibility to be used with a bipod by infantry like a light machine gun, or mounted on a heavier tripod or vehicle and used similar to a heavy machine gun. For this reason, a medium machine gun is sometimes referred to as "General Purpose Machine Gun (GPMG)" or "Universal Machine Gun".

The first real MMG was the Browning designed M1919 medium machine gun. This is a weapon that fires .30 caliber rifle cartridges from an ammunition belt. It was designed as an air-cooled variant of the M1917 heavy machine gun. Unlike the M1917 which weighs 103 lb. (47 kg.), the M1919 only weighs 31 lbs. (14 kg.) The minimum number of people needed to operate it is two, but sometimes upto four people were involved: a gunner (who fired the gun and also carried the tripod and some ammunition, when moving the gun), an assistant gunner (who fed the ammunition and carried the gun, when on the move) and two other people to carry extra ammunition, barrels, tools etc.

US Marines operating a M1919 A4 during World War II. Click on the image to enlarge. Public domain image.

This weapon was heavily used in World War II by different branches of the US military. It was used by infantry troops, mounted on jeeps, tanks, armored personnel carriers, aircraft etc. and continued to be used well into the Vietnam era. It was also used by other military forces around the world and modified to take other rifle cartridge calibers as well, such as .30-06, 7.62x51 NATO, .303 British, 7.62x54 mmR etc. In fact, it is still in use in some parts of the world.

In our next post, we will look at some more medium machine guns.

Heavy Machine Guns - III: Modern HMGs

In our last couple of posts about heavy machine guns, we saw that they were weapons designed to fire rifle cartridges for long periods of time. Since they were designed for firing in automatic mode for hours, the designs were bulky and the early machine guns were water-cooled, which contributed even more to the weight. Therefore, these weapons needed multiple people to operate effectively and inconvenient to move around and were mainly used as defensive weapons. Heavy machine guns of this type were used extensively in the trench warfare conditions of World War I, against enemy infantry.

World War I also saw the introduction of armored vehicles, such as the British Mark-I tank and the German Junkers J.I airplane. Against such armor, ordinary infantry rifle ammunition (like the .30-06) was useless. Therefore, there was a need for a weapon that could defeat lightly armored vehicles, buildings, aircraft etc. and could do so at longer ranges. In 1917, General Pershing posted a request back to the US Army Ordnance Department, asking for a rifle to be designed, that could fire a bullet of at least .50 inches (12.7 mm.) diameter at a velocity greater than 2700 feet/second (820 meters/second). The famed designer, John Browning, went to work on this request. He took his earlier .30 caliber machine gun model and scaled it up to fire a .50 BMG (12.7x99 mm.) caliber cartridge. His initial design used water cooling, just like other heavy machine guns of that era. The design came too late to be used in World War I, but was accepted later by the US Army and Navy as the M1921 (curiously though, despite the name, it actually went into production in 1929!).

After Mr. Browning passed away in 1926, further development work on this gun went on, led by Dr. S.H. Green. By studying the needs of the US Army, Navy and Air Force, Dr. Green realized that a single machine gun model could not accommodate everyone's requirements. Hence, he redesigned the M1921 to a model that could be changed into seven different .50 caliber machine guns, all using a common receiver component, but switching the other components such as the barrel, water jacket etc. The new model machine gun was called the M2 heavy machine gun and was manufactured in its different versions by Colt, starting in 1933. One of the versions did not have a water jacket, but instead had a heavier air cooled barrel, which was designed to be quickly changed. The lack of the water jacket meant that the barrel had to have a larger surface area and have more mass to compensate, therefore this variant was called the M2 HB (HB standing for "Heavy Barrel"). However, this version was lighter compared to the water-cooled versions: the water-cooled M2 versions weigh about 121 lbs (55 kg.) and the air-cooled M2 HB only weighs 84 lbs (38 kg.) in comparison. Another even lighter version, with a thinner barrel designed exclusively for aircraft use, only weighs 60 lbs (27 kg.) and was used by many US aircraft in World War II.

It must be noted that World War II changed the nature of warfare in several ways. The German Blitzkrieg strategies showed the effectiveness of maneuver warfare and static machine gun positions that were so effective until World War I, became obsolete and useless. In this environment, a lighter heavy machine gun model that can be moved around relatively easily, is much more useful than a heavier water cooled model.

M2 Heavy Machine Gun on a M3 tripod. Public domain image.

While the M2 HB weighs 84 lbs. (38 kg.), it must be noted that the M3 tripod stand that it is mounted on weighs an additional 44 lbs. (20 kg.). The gun is also designed to be mounted on jeeps, armored vehicles, ships or anti-aircraft turrets. It can fire a variety of rounds, ranging from standard ball ammunition to armor piercing, incendiary etc. This weapon was very successfully used by various branches of the US military in World War II and continues to be used by the US military to this day. It is also used by military forces of many other countries in the world. It exemplifies the modern definition of the heavy machine gun, as we know it today.

To summarize, the early heavy machine guns were designed to use standard rifle ammunition, were water cooled and bulky, capable of long range firing, and designed to be used in static defensive roles. The modern definition of a heavy machine gun is a weapon that is designed to use much larger ammunition calibers, is air-cooled, has quick change barrels to solve overheating issues, is less bulky than water-cooled models, capable of long range firing, is designed to be moved around relatively easily, and can be used in both defensive and offensive roles. Modern heavy machine guns are designed to be used, not only by infantry, but also by jeeps, tanks, humvees, boats, ships, aircraft etc.

A M2 HMG in a firebase overlooking the Korengal valley in Afghanistan. Click on the image to enlarge. Public domain image.

US Marine from the 24th Marine Expeditionary Unit with a vehicle mounted M2 heavy machine gun. 

Click on the image to enlarge. Public domain image.

Modern heavy machine guns include the above mentioned M2, the Soviet DShK 1938 (another World War II era design), the Russian Kord HMG etc.

Heavy Machine Guns - II

In our last post, we looked at the early developments in heavy machine guns and the work done by Hiram Maxim. We will continue our studies on this topic today.

When we last left off, Hiram Maxim had invented the Maxim gun and had founded a company in England to manufacture them. What was not mentioned in the previous post was that he took on a partner for funding the new Maxim Gun Company. This partner was Albert Vickers, son of Edward Vickers, who was one of the founders of a prosperous steel foundry business and also had interests in manufacturing armor plating and shipbuilding. In 1896, the parent Vickers company bought out the Maxim Gun Company and got into the machine gun manufacturing business as well. Vickers took the basic Maxim gun design and simplified the firing mechanism and also used more modern alloys in the construction, thereby reducing its weight slightly. The Vickers machine gun was formally adopted by the British army in 1912 and was used pretty heavily in World War I, both by the army and the airforce (it was fitted into several British and French fighter aircraft).

Vickers machine gun in action during World War I. Click on the image to enlarge. Public domain image.

Like its predecessor, the Maxim machine gun, the Vickers also has a barrel surrounded by a water jacket, in order to cool down the barrel. Upon firing the barrel rapidly, the water would turn into steam and exit out via a port at the muzzle end, into a separate steam chest. Here, it would condense back into water. This system has the advantage that the rising steam does not give away the gunner's position and the water can be reused. It was recorded that if the water ran out, crews were known to pee into the water jacket.

In British use with the .303 cartridge, this weapon has a range of over 4000 meters. The gun weighs about 30 lbs (13.6 kg.) by itself, without any ammunition or water. With a full load of water (about 4 liters) in the water jacket, it weighs about 40 lbs (18 kg.). Then, there is the tripod stand, which weighs about 50 pounds (23 kg.) and the ammunition boxes, which contain 250 cartridges held in a cloth ammunition belt and weigh about 22 lbs (10 kg.) each. In addition to this, the weapon also comes with spare barrels, steam chest, pipes etc. With all this weight, the gun needed about six to eight people in a crew to operate it: one to fire the gun, another to assist with feeding the ammunition and reloading it and the rest to carry the weapon, extra ammunition and spare barrels. If the gun needed to be moved, the crew would disassemble it into lighter component parts, while one of them stood guard with an ordinary rifle.

The gun was designed to fire 10,000 rounds per hour, after which the barrel would have to be replaced by a new one. With a trained crew, this barrel replacement operation only took a couple of minutes to accomplish. Therefore, the gun could be used to fire almost continuously for very long periods of time. In August 1916, the British Army's 100th Company of the Machine Gun Corps fired their ten Vickers guns continuously in battle for about 12 hours straight. During this time. they interchanged about 100 barrels and it is recorded that they fired over 1 million cartridges without a single failure!

It was during World War I that the classification between heavy machine guns and light machine guns started. Light machine guns like the Lewis gun were issued to normal infantry units. Heavy machine guns like the Vickers were issued to new units called Machine Gun Corps.

As the reader can probably see, the differences between the light and heavy machine gun classifications now become clear. Light machine guns are lighter, come with bipods and are designed to fire short bursts of ammunition, whereas heavy machine guns are much heavier, are mounted on tripods or vehicles and can fire on automatic for much longer periods. Light machine guns are issued to advancing infantry units to support an attack, whereas heavy machine guns are more geared towards staying at a fixed position and defending against advancing infantry or cavalry.

The Vickers gun was known for reliability and was sold to several countries in a variety of calibers. It was in service with various countries from about 1912 to 1968. Unlike the light machine guns that we studied before, this gun is capable of firing almost continuously, literally for hours.

In our next post, we will look at the modern definition of heavy machine guns.

Heavy Machine Guns - I

In our last post, we looked at light machine guns. In today's post, we will look at another class of machine guns, the Heavy Machine Gun (often abbreviated as HMG).

In the late 1800s, there arose a need for a firearm that could fire in automatic mode, with good accuracy over longer ranges, for a long amount of time. Such a weapon could be used by a small group of soldiers in a key position to defend against a much larger group of enemies armed with inferior weapons and prevent them from advancing. Unlike light machine guns, these weapons needed to fire in automatic mode for much longer periods. This led to the development of heavy machine guns, weapons that can literally lay down huge volumes of fire, for very long periods of time.

The first heavy machine gun in history was the Maxim gun, invented in 1884 by Sir Hiram Maxim, an American inventor settled in England (he later became a British citizen in 1900). He was a prolific inventor and invented several items including a curling iron, several gas and steam engines, electric light bulbs, automatic sprinklers, motor cars etc. In 1882, he was in Vienna and ran into another fellow American that he knew from his time living in America, who informed him that "Hang your chemistry and electricity! If you want to make a pile of money, invent something that will enable these Europeans to cut each others' throats with greater facility." As a child, Sir Maxim had fired a large gun and had been knocked down by the recoil. This incident inspired him to invent a recoil operated machine gun (he also patented gas operated and blowback systems between 1883 and 1885). While he was inventing his gun, he announced in the local papers that he was experimenting with a new type of gun in his garden and advised his neighbors to keep their windows closed, in order to avoid getting injured by broken glass!

Maxim's first prototype weighed around 26 pounds (11.8 kg.), but was not capable of firing for long periods of time because of overheating problems. To solve this issue, he put a water jacket around his barrel. He also increased the caliber to fit a .303 British rifle cartridge. This made his rifle design heavier and it weighed around 60 pounds (27.2 kg.)

A Maxim machine gun. Click on the image to enlarge.

Image licensed under the Creative Commons Attribution-Share Alike 3.0 License by Jonathan Cardy at Wikipedia

Such a heavy gun required a team of people to operate: one man to fire the weapon and the others to reload ammunition, refill water, spot targets, help carry the gun and ammunition from one position to another etc. While Maxim tried to sell his invention to various European countries, many of them were suspicious about machine guns in general, because of jamming issues on previous models. Luckily for Maxim, the British had appointed Sir Garnet Wolseley as commander-in-chief in 1888 and he was a big believer in new technologies and placed an order for 120 Maxim machine guns in October, using the same .577/450 cartridges of the Martini-Henry rifle. The Maxim guns proved their worth in 1893/1894, in the First Matabele War in Africa., where a small unit of British soldiers armed with just four Maxim guns held off a force of 3500-5000 African Ndebele warriors. After this and several other encounters, other governments started to take notice and placed orders for heavy machine guns as well.

Early Maxim guns had a problem of heavy smoke obstructing the view of the gunner very quickly, but the invention of smokeless powders solved this issue. Incidentally, Hiram Maxim himself was one of the pioneers of smokeless powders and he and his brother, Hudson Maxim, were granted a patent for a particular type of smokeless powder. However, the patent was issued in the name of "H. Maxim" and his brother took advantage of this to stake a claim for the patent and later moved back to the United States, where he developed several more explosives and sold the rights to the DuPont Chemical Company. Because of this patent dispute, Hiram Maxim stayed in Europe, while his brother moved back to the United States and the brothers never spoke to each other ever again.

Due to years of experimenting with loud guns, Sir Hiram Maxim's hearing was damaged and he began to go deaf later in life. In a twist of fate, a device that could have saved his hearing, the Maxim silencer (suppressor), was invented by his son, Hiram Percy Maxim in 1908.

In our next post, we will look into further developments of heavy machine guns.

Light Machine Guns

In our discussion about general features of machine guns, we discussed different classes of machine guns. Today, we will study the first of those classes, the light machine gun (often abbreviated as LMG).

Light machine guns were originally developed to support infantry squads, by providing short bursts of suppressive fire, designed to keep the enemy's heads down and allow friendly soldiers to advance. The first light machine guns were developed around World War I. Early machine gun examples include the Browning BAR M1918, Lewis gun, Madsen machine gun etc. In present day military forces, many infantry units carry one LMG per fire team or squad.

Browning Automatic Rifle (BAR) M1918, designed during World War I. Click on the image to enlarge. Public domain image.

A Lewis gun. Click on the image to enlarge. Public domain image.

The word "light" is a bit of a misnomer, because most LMGs are heavier than the assault rifles that the rest of the team carries. However, they are lighter than the other classes of machine guns that we are going to study in the following posts.

Light machine guns are generally designed to use the same ammunition as the rifles carried by the rest of the unit. This feature allows the different soldiers to share ammunition during a battle. For instance, the Browning M1918 uses .30-06 ammunition, the same as the M1903 rifle carried by US soldiers in World War I, the M249 SAW uses the same 5.56x45 mm. ammunition used by M16 rifles etc. Since LMGs are designed for automatic fire, many feature high capacity magazines, such as drum magazines, pan magazines or ammunition belts. However, some models of LMGs are designed to use the same box magazines as the assault rifles carried by the rest of the unit, so that they can share both magazines and ammunition between themselves. Some newer LMGs are designed to use multiple methods of feeding ammunition. For instance, the FN Minimi, the M249 SAW, IMI Negev and the Heckler & Koch MG 43 (now known as the MG4) are designed to use both ammunition belts, as well as box magazines. This allows the machine gunner maximum flexibility in using ammunition and magazines during a battle.

A M249 equipped with an ammunition belt. Click on the image to enlarge. Public domain image.

While the LMG is light enough to be carried by a single soldier and fired from the hip, it is generally fired from the prone position. Because of this, many LMGs have a bipod attached to the front of the barrel, to allow the user to comfortably operate the weapon from the prone position.

In recent times, many LMGs are modifications of an existing assault rifle design. Examples of these include: RPK (Russian LMG design based on the AK-47), Steyr AUG LMG (Austrian rifle based on the Steyr AUG rifle family), INSAS LMG (Indian rifle based on the INSAS rifle family) etc. However, the LMG versions are generally designed with longer and heavier barrels, to sustain automatic fire for longer periods of time without overheating. Some models (such as the Steyr AUG LMG) have quick change barrels to solve the overheating problem. The parts of the action are also designed to be more robust than the assault rifle versions, in order to shoot in full automatic mode for longer periods of time.

An INSAS Light Machine Gun. Click on the image to enlarge.

A Bren gun. Public domain image.

The above image shows a Bren gun Mark I. Note the curved box magazine mounted on top of the rifle and the carrying handle in the middle of the gun, which also doubles as a tool to remove a hot barrel. Later models came with heavier chrome-lined barrels, which reduced the need to interchange barrels. The Bren gun was first adopted in 1938 by the British, produced by various commonwealth countries (UK, Australia, Canada, India) over the years and is still being manufactured currently in India!

The Madsen machine gun also has a long history, being originally manufactured by Denmark in 1902 and still going strong in the hands of Brazilian military police, well into the 21st century! It just goes to show that good designs can last a really long time.,

In our next post, we will study another class of machine guns: the heavy machine gun.

Early Machine Guns

In our last post, we looked at some basics about machine guns. In today's post, we will study some early developments in machine gun history and what technologies needed to be invented along with them.

One of the early developments in weapons capable of firing multiple shots before reloading was the Puckle gun, which we already studied some time ago. This was invented in 1718 and is the precursor of the revolver.

A Puckle gun. Click on the image to enlarge. Public domain image.

There were also other multi-shot weapons invented later, such as the Mitrailleuse gun and the Belton flintlock, but the first real practical machine gun was the Gatling gun, invented by Richard Gatling in 1861.

In order to have a rapid firing weapon, it was necessary to have a way to automate/quicken the reloading process and the invention of the cartridge came in handy here. Early gatling gun models used paper cartridges and percussion caps, because these were the same technologies used by US Army infantrymen of that era -- in fact, the Gatling gun was designed to use the same caliber cartridges. However, this model was prone to jamming. The second model used the rimfire cartridge instead. Rimfire and centerfire cartridges made the Gatling more reliable. Metallic cartridges also made it possible to provide a better seal in the chamber of the firearm, because the hot gases from a fired cartridge expands the metal case and seals the back of the chamber.

Another technology that made it possible for modern machine guns was the invention of smokeless powder. Early Gatling guns used black powder cartridges. With black powder, the smoke rapidly makes it hard for the operators to see what is going on. On top of that, black powder leaves behind a lot of dirty residue and this can cause the mechanism of a machine gun to jam. Smokeless powders produce a lot less residue, therefore the gun can fire for longer periods without risk of jamming.

Improvements in metallurgical techniques also helped, because it made it possible to make gun parts which perform reliably for extended periods of time and resist heat better as well.

With that said, heat dissipation has always been a problem in machine gun design. In the case of the Gatling gun, the problem was solved by using multiple barrels. With multiple barrels, the weapon can fire at a higher rate, but each barrel is rotated after each shot and therefore has time to cool before it fires another shot. However, the presence of multiple barrels makes the overall weapon heavier. Water cooling and quick-change barrels are other techniques that were historically used by other machine guns to solve the same issue. Interestingly, the use of multiple barrels in a gun was revisited in modern times, with the invention of the minigun and the multi-shot cannon used on the A-10 Warthog aircraft.

Also, the idea of using an electric motor to power a gun is a lot older that most people realize. In fact, in 1893, Richard Gatling received a patent for a gatling gun powered by an electric motor!

Machine Guns - General

In our last few posts, we studied different feed systems such as ammunition belts, chain feeds and feed strips. All these mechanisms are generally used with machine guns. Therefore, in the next series of posts, we will study all about machine guns.

A machine gun is a firearm that is capable of fully automatic fire. What this means is that as long as the firearm has ammunition available to it and the trigger is pulled, it will continue to load and fire ammunition automatically. Machine guns are capable of firing at high rates of several hundred rounds per minute and are designed to keep firing for considerable periods of time. The capability of maintaining sustained fire for long periods of time is what distinguishes a machine gun from an automatic rifle or an assault rifle (both of which can fire on full-auto only for limited periods of time).

US military doctrine has another interesting way of classifying automatic rifles versus machine guns. If the fully automatic firearm is operated by a crew, then it is a machine gun, but if a fully automatic firearm is operated by a single person, then it is an automatic rifle. In many cases, weapons fall exclusively into one of these two designations, however, we have one major oddball that falls into both categories -- the M249. US Army Field Manual FM 3-22.68 ("Crew-Served Machine Guns") describes the M249 as both an automatic rifle and a machine gun! Quoting from the manual chapter 4, section 5, paragraph 4-207, "Both the M249 automatic rifle and the M249 machine gun are identical, but its employment is different. The M249 automatic rifle is operated by an automatic rifleman, but its ammunition may be carried by other Soldiers within the squad or unit. The M249 machine gun is a crew-served weapon."

Machine guns can be portable as well as mounted and therefore, they are generally classified based upon size.

Before we dig deep into the topic, let us talk about submachine guns, which are portable firearms that are designed to fire pistol-sized ammunition. While they have a high rate of fire, some authorities do not consider these as "true machine guns" as they are not capable of sustained fire for long periods of time. Examples of these would be the Thompson submachine gun (which actually coined the term "submachine gun") also known as the Tommy gun, Chicago typewriter, Trench broom etc., Heckler & Koch MP5, Uzi etc. All these weapons are designed to fire pistol sized ammunition such as .45 ACP, 9 mm Parabellum etc.

Next, we have true machine guns like the Light machine gun, Medium machine gun, Heavy machine gun, General purpose machine gun which all use larger ammunition calibers (rifle calibers or larger). These weapons are generally heavier than other automatic weapons (even the "light" machine gun is heavier than an assault rifle, for instance). Examples of these would be the Lewis gun, the Bren gun, MG-34, Browning M1917, Browning M2, M60 etc.

A Lewis gun. Click on the image to enlarge. Public domain image. 

A M60 machine gun. Click on the image to enlarge. Public domain image.

We will study more into these various types of machine guns in the following posts.

Finally, we have weapons in the autocannon category. The difference between an autocannon and a machine gun has largely to do with the type and size of ammunition. If the firearm uses ammunition greater than 16 mm. diameter, or if it uses large caliber explosive rounds, then it is considered an autocannon rather than a machine gun. Examples of an autocannons include the M242 Bushmaster (which we studied briefly, when recently studying about chain guns), Oerlikon 20 mm. autocannon etc.

Since machine guns are designed to fire on automatic for longer periods of time, they tend to overheat quickly. Hence, many of them are either designed to have a built in barrel cooling system or feature a quick-change barrel replacement system. For the same reason, most machine guns are also designed to fire from an open-bolt, so that the breech area can be more efficiently air-cooled when the gun is not firing.

In the next few posts, we will study all about various types of machine guns and their history.

Actions: Recoil Action: Short Recoil Operation

In our previous post, we studied the basics of recoil operated actions. In this particular post, we will study one of the types of recoil operated actions, i.e. the short recoil operation.

This action type has a long history, being the action that was used in the first machine gun ever invented, i.e. the Maxim machine gun. It is also the action of choice for most semi-automatic and automatic pixels that use 9 mm. Luger (9x19 mm.) cartridges or bigger. Smaller and lower powered cartridges are used with blowback actions that we studied last month, but once the cartridges get beyond a certain size and power, a blowback action cannot be used any more and most modern pistols therefore use a short recoil operation.

As we noted in our previous post, one of the key differences between a blowback action and a recoil operated action is that a recoil operated action has the bolt (i.e. the metal block that holds the cartridge in the chamber before firing) is locked at the point of firing, whereas a blowback action merely has it held under spring pressure. This enables the recoil operated action to fire heavier cartridges. Also, as we noted previously, in a recoil operated action, some parts of the weapon are allowed to recoil backwards, whereas other parts are held stationary relative to the recoiling parts. In a short recoil action, the parts that are allowed to recoil are the barrel and the bolt.

At the point when the bullet is fired, the barrel and the bolt are locked together and move backwards due to recoil. After a short distance of travel (a few mm. in the case of pistols and a few caliber lengths in the case of machine guns), the bolt and the barrel disengage from each other. How this is achieved is what differentiates various short recoil operation systems. In some cases, the barrel is slowed down, in other cases, the bolt is accelerated. In either case, the barrel stops moving, whereas the bolt continues to move backwards and compresses a recoil spring and also extracts the old cartridge case at the same time, which is ejected via a side port. The recoil spring then pushes the bolt forwards and as the bolt moves forwards, it picks up the new cartridge from the magazine and pushes it and the barrel forwards. When the barrel reaches its forward position again, the bolt and barrel lock again and the weapon is ready to be fired.

As was mentioned above, in some systems, the barrel is slowed down to separate the barrel from the bolt. Weapons that use this include the classic Colt M1911 pistol designed by John Browning, all Glock pistols, Smith & Wesson, FN Browning, SIG Sauer etc.

In the case of the Browning designed Colt M1911, the bolt, barrel and slide all move backwards together initially, but then a barrel link tilts the barrel downwards. As the barrel tilts, the barrel locking lugs unlock themselves from the slide recesses. The bolt and slide continue to move backwards and an extraction claw on the slide also pulls the spent cartridge out of the chamber.

An ejector strikes the back of the spent cartridge and pushes it out of the extraction port, as the slide and bolt continue to move backwards. When the slide and bolt reach the back of the pistol, the recoil spring pushes them forward and during the forward motion, the slide locks back into the barrel and the three pieces then move back together. The two animated movies below show how this works.

In the case of Glock, SIG Sauer and most recently designed automatic pistols, this mechanism is even more simplified. There is a downward inclined ramp attached to the back of the barrel. As the barrel and slide move backwards, the ramp contacts a fixed stud on the pistol's frame. This causes the back of the barrel to move down (and the front to tilt up), which moves it out of engagement with the slide. The rest of the action is similar to what was described earlier. The animation below shows exactly how this works:

In the above three animations, the one thing is common is that the bolt and barrel initially move backward together and are then separated by slowing down the barrel while leaving the bolt and slide free to continue moving backwards.

Another way to achieve this separation is by accelerating the bolt after they both move back together. This mechanism is most commonly used today in the 7.62 mm. and 12.7 mm. M2 machine guns invented by (surprise, surprise) John Browning! The 12.7 mm. M2 is still used in the famous Abrams tank, as well as most other western tanks, which shows the reliability and timelessness of this design. In the M2 machine gun, the barrel and bolt initially recoil together about 10 mm. backwards and then a rotating cam in the receiver disconnects the bolt from the barrel. The barrel has an extension in the back and bottom of the barrel. After the bolt and barrel are disconnected, this extension then strikes a short, curved lever. The lever is pivoted so that it has a mechanical advantage and therefore it pushes and accelerates the bolt rearward. A fixed stud stops the barrel extension, which also halts the barrel, while the bolt continues rearward. As before, we have an animation to show how it works:

We will continue studying short recoil operations tomorrow, where we will deal with some more historical short-recoil operated weapons such as toggle-bolt short recoil actions. It'll be interesting reading!