Firearms History, Technology & Development

In our previous post, we'd studied the helical magazine, as invented by Calico Inc. in 1985. However, there is a precusor to this that was invented in the 19th century, called the Evans Repeating Rifle, that also used a helical magazine of sorts. We will study that particular rifle in today's post.

The Evans rifle was invented by Warren R. Evans, a dentist from the state of Maine. He received his first patent for an improved magazine in December 1868 and another patent for an improved gun lock in 1871. With these two patents, he entered his prototype rifle into the US Army trials of 1872, but his rifle was not selected due to mechanical issues. However, he wasn't the only mechanically inclined person in his family and his brother, George Franklin Evans, was also a talented machinist. He and his brother joined forces with a few other investors and started the Evans Rifle Manufacturing Company in Maine in 1873, to manufacture this rifle design for the commercial market.

An Evans Repeating Rifle

This rifle is a lever-action firearm and the trigger guard doubles as the lever that operates the action. Like the Spencer rifle (which we studied earlier here and here), this rifle also has a magazine inside the stock. However, the Spencer rifle has a tubular stock, whereas this rifle has a helical type feed mechanism that uses an Archimedian screw (The screw gets its name from the fact that it was supposedly invented by Archimedes, but was actually invented by Assyrians about 350 years earlier. It was used for pumping water in the ancient world). In the case of the Evans rifle, the screw thread is used to push cartridges into the chamber.

Disassembled Evans Rifle Magazine.

The above image shows a disassembled Evans rifle magazine. The barrel is facing to the left and the two halves of the magazine occupy most of the picture. The screw thread can be clearly seen inside the magazine. Unlike the helical magazine that we studied in the previous post, this one is not spring loaded. Instead, upon operating the trigger guard lever, the screw rotates 1/4th of a turn, which pushes the next cartridge into the chamber.

Like the Spencer rifle, new cartridges are pushed in from the base of the buttstock. Unlike the Spencer rifle's tubular magazine, this is safe to use with centerfire cartridges using spitzer type bullets because the tip of each bullet does not touch the primer of the previous cartridge. The Evans rifle holds 34 cartridges in its magazine, compared to the Spencer's seven cartridge tubular magazine and the Winchester M1873, which holds 15 cartridges in its tubular magazine.

About 12000 to 15000 rifles were manufactured by the company during its existence. Evans rifles were given to several foreign military officers and politicians and were also endorsed by celebrities of the day, such as Kit Carson and Buffalo Bill Cody. In fact, Kit Carson even enthusiastically submitted the following testimonial to the Evans company, saying: "At twenty paces, have, with this rifle, shot the eyebrows from my wife, and every night regularly, in the presence of an audience I shot an apple from her hand, a pipe from her mouth, a penny from her fingers, or snuff a candle from her hand. I think the Evans is the safest and most complete repeating system ever devised."

An enthusiastic endorser of the Evans rifle. An Apache Indian holding an Evans rifle from around 1880. Public domain image.

However, there are a few disadvantages of this design as well:

The first is that the new cartridges are loaded through the butt plate, not the front of the magazine (unlike the Calico helical magazine that we studied in the previous article). This means that if the user loads a single cartridge into the magazine, he (or she) has to pull the lever 33 times so that the cartridge works its way through the magazine into the chamber.

Another issue is that the lever controls both the feeding and loading of the magazine at the same time. This presents problems when trying to refill a partially filled magazine On other firearms, such as the Winchester M1873 with a tubular magazine, or the Calico submachine gun, the magazine feed is independent of the action. Therefore, if the user fires (say) three cartridges, the user can then simply push in three more cartridges and top off the magazine. On the Evans rifle, if the user has a fully loaded rifle, then fires three cartridges and then wants to top off the magazine, the user must pull the lever each time a new cartridge is pushed through the butt plate to load the magazine. This means that loading three cartridges through the butt plate will eject three more cartridges from the top of the magazine and there will be a gap in the magazine before the last three cartridges can be fired. The only way that a user can always keep the magazine topped off is by firing a single cartridge, then pushing a new cartridge into the butt plate and operating the lever to eject the old cartridge case and load the new cartridge into the magazine. This problem was later partially solved by George Evans in 1877, by making a design modification that allowed the user to load the rifle from from the breech end, without disturbing the cartridges already in the magazine.

This rifle also uses specially designed cartridges (the .44 Evans Short and .44 Evans Long for later models), which were not used by any other firearms and were not easily available either. The only manufacturer of this ammunition was the Evans Rifle Manufacturing Company themselves and they did not manufacture this ammunition in enough quantities to meet the market demands. The rifle also had mechanical issues and was affected by dust as well. These were some of the reasons why it was not to be accepted by the US Army in 1872. The company tried to enter the commercial market, but the lack of availability of ammunition for it caused it to not sell well. Also, after the Civil War (1861-1865), there was a surplus of firearms available on the market for cheap and the company could not compete on price against older established firearms companies. By 1879, the company went bankrupt and its assets were sold by March 1881.

In today's post, we will study a type of magazine that has been used on only a few firearm models so far. Today's subject of study will be the horizontal magazine.

One of the well known weapons to use the horizontal magazine is the Fabrique Nationale FN P90 personal defence weapon.

The transparent piece lying flat at the top of the weapon is the horizontal magazine. In the above image, the cartridges emerge out of the magazine on the right side. The picture below shows what the magazine looks like, when it is detached from the firearm:

A horizontal magazine. Click on the image to enlarge.

Image released under a Creative Commons Attribution-Share Alike 3.0 Unported license by ROG5728

It consists of two rows of cartridges in the magazine, which lie at right angles to the barrel, when the magazine is attached to the firearm. A spring at the back of the magazine pushes the cartridges out towards the feed lips (the circular part) of the magazine. Near the feed lips is a stationary spiral ramp that combines the two rows of cartridges into a single row and also rotates the cartridges by 90 degrees as they emerge of the magazine, thereby loading into the chamber with the proper orientation. The magazine is made of a translucent plastic material, allowing the user to see how many cartridges are left in the magazine. An FN P90 magazine can hold 50 cartridges when fully loaded.

Public domain image of the FN P90 magazine patent. Click on the image to enlarge.

The above image shows some of the details of the magazine, taken from one of the pages of the patent claim. This particular magazine design was invented by Rene Predazzer and the full details of the patent claim may be found here. Figure 6 in the image above shows how the double rows of cartridges are combined into a single row by the ramp and rotated before exiting the feed lips.

Another firearm that uses a horizontal magazine is the AR-57, which is basically a firearm with an AR-15/M16-style receiver chambered to use the FN P90 cartridges and horizontal magazine. This was designed by Rhineland Arms Inc.

However, the FN P90 is not the first user of a horizontal magazine. There exists an US patent claim from 1923 by Arthur Kottas, a retired officer of the Austrian Army, where a horizontal magazine is described (in fact, his US patent claim mentions that he first patented his invention in Austria on August 16th, 1918, so the actual invention date is even earlier). The details of his patent may be found here:

Public domain image of Arthur Kottas' magazine design from 1923. Click on the image to enlarge.

In the Kottas patent, a single row of cartridges is placed at right angles to the barrel and rotated into position before entering the chamber.

There also exist other US patent claims from 1948 by Woodville B. Conway (details may be found here) and in 1953 by John L. Hill (details may be found here).

Public domain image of John L. Hill's patent from 1953. Click on the image to enlarge.

In both the Conway and Hill patents, note that the magazines contain double stack of cartridges which are combined into a single stack and then rotated before exiting the chamber. The same double stack idea is used in the FN P90 magazine as well, except that the magazine is placed at the top of the firearm instead of underneath it.

The nice thing about horizontal magazines is that they can contain a large number of cartridges for their size. For instance, the FN P90 magazine can hold 50 cartridges, which is pretty amazing considering the size of the firearm. Also, compared to a box magazine which projects out of a weapon, this type of magazine sits horizontally and flat inline, which makes the firearm much more balanced and convenient to hold. Since the magazine stores cartridges side by side, it can safely be used with centerfire cartridges using spitzer-type bullets. In the case of the FN P90, the magazine is made of a semi-transparent plastic, which allows the user to see how many cartridges are left in the magazine.

In our last post, we looked at horizontal magazines. In today's post, we will look at a type of magazine that was used in the 19th century: the turret magazine.

During the middle of the 19th century, Samuel Colt perfected the revolver and obtained patents for revolver cylinders. Hence, anyone who attempted to make a revolver type firearm during that period, was likely to infringe on his patents and would have been forced by law to not manufacture such weapons. Turret magazines were seen as one way to bypass Colt's patents.

Turret magazines are simply drums where the cartridges are placed facing radially outwards. There were two types of turret weapons developed: horizontal turrent firearms and vertical turret firearms. In the horizontal turret firearm category, we have a few examples shown below:

A Daniels Turret Rifle. Click on the image to enlarge

A Cochran revolver shown with turret magazine loaded and unloaded. Click on the images to enlarge

In the above pictures, we see some firearms with horizontal turret magazines. As the reader may note, the magazine is horizontally positioned on the firearm. Percussion caps are placed on the nipples at the underside of the turret magazine, to ignite the gunpowder loaded into the chambers. Note that in the above examples, the hammer of the firearm is placed under the firearm and in front of the trigger and the magazine is accessed from the top. The pictures of the Cochran revolver, in particular, show how the magazine is loaded and unloaded from the top of the firearm. John Webster Cochran of New York, received about 25 different firearm patents and was well known for his "recoil-free" turret weapons. Many of his turret designs were manufactured under license by the company of C.B. Allen of Springfield, Mass.

There is also the vertical turret magazine and in this category, we have:

Porter turret rifle with spare magazine. Click on the image to enlarge.

Porter turret rifle, showing how the magazine is loaded. Click on the image to enlarge.

A French made Goudry turret revolver, open and closed. Click on the images to enlarge.

Porter turret rifles were invented by T.P. Porter and were seen as competitors to Colt's revolving rifles. They were used by many pioneer settlers moving towards the Western United States. Turret magazines hold about 9-20 cartridges, which is pretty high capacity for the period that they were used.

Both horizontal and vertical turret weapons are somewhat dangerous, because a loaded weapon will always have at least one of its cartridges pointing directly back at its user. After firing a cartridge, there is the danger of stray sparks flying into other chambers and a chain reaction discharging the other chambers as well. This actually happened on some occasions and resulted in fatal accidents. Samuel Colt, being a crafty businessman, took full advantage of this news and advertised that his revolving system was much superior and reliable compared to any turret firearms. In fact, Colt even falsely spread a rumor that the inventor of the Porter rifle (T.P. Porter) was killed when demonstrating his own rifle to customers! These rumors had the effect of halting sales of Porter rifles and turret magazines in general and Mr. Porter spent the rest of his life making more traditional firearms.

We have been talking about magazines in the last few posts. In today's post, we will look at something that is not quite a magazine, but definitely holds ammunition. In today's post, we will study ammunition belts.

While an ammunition belt can hold and feed cartridges into a firearm, it does not fall into the category of "magazine", because it has no feeding mechanism of its own. Instead, an ammunition belt relies on a separate feed system built into the rifle, to extract and use the ammunition. Belts are generally used with firearms that have a high rate of fire (e.g.) machine guns.

An M60 machine gun with an ammunition belt. Click on the image to enlarge. Public domain image.

Early ammunition belts were made of cloth, with evenly spaced pockets to place cartridges into. These were used in early machine guns, such as the Maxim gun, Vickers machine gun, Browning M1919 machine gun etc. The feed mechanisms on these early guns are designed to pull each cartridge from a belt backwards and then feed the cartridge forwards into the chamber. The empty belt is pushed out of the other side of the gun and it may be refilled again. The good thing about cloth belts is that they are easily reusable and can be quickly refilled. The problem with cloth belts is that they tend to be somewhat prone to jamming, especially because cloth tends to deteriorate if it absorbs water, oil, cleaning chemicals etc. Also, the empty side of the belt may get tangled up with vegetation and debris as it comes out of the gun. This is usually a problem, if the gunner wants to move the gun.

An ammunition belt made of cloth.

Because of the jamming issues, ammunition belts are now generally made of metal links. Metal links have the advantage that they are not affected so much by oil or cleaning solvents. However, they tend to be heavier than cloth belts.

Newer ammunition belts are made using disintegrating metal links. What this means is that each link is connected to the round ahead of it in the belt. As each cartridge is stripped out of the belt and loaded into the firearm chamber, this causes the link holding the cartridge to fall out of the belt and the link can be ejected out of the bottom of the gun. This means that there is no empty belt coming out of the other side of the gun and it can't tangle up with anything. Therefore, the operator can move the gun without worrying about a half-empty belt dragging on the ground. On the other hand, disintegrating belts are not as easy to reload as non-disintegrating types.

The above video shows a user using a belt with disintegrating links. As you can see, the links holding the ammunition fall out of the gun as each cartridge is fired and there is no empty belt coming out of the side.

In general, cloth belts are cheaper to manufacture than metal belts and more flexible, but are also more prone to getting affected by rain, oil, cleaning solvents etc. Metal belts are more expensive to manufacture, but are more reliable, especially in bad weather conditions.

Belts allow the user to carry a lot of ammunition and are relatively lightweight. This is why they are used on firearms with high rate of fire (e.g.) machine guns. Many machine guns have a box on the side, where a folded belt may be placed. The picture of the M60 above shows one such ammunition box. This allows the user or an assistant to conveniently carry ammunition around and also provides the belt some protection from rain, snow, mud etc.

The previous article on the topic of ammunition belts prompted a vague recollection in your humble editor's mind of another feeding mechanism: chain guns. We will study them in today's post.

A chain gun uses a continuous chain that is driven around a couple of sprockets, to feed the firearm. The chain has chambers where cartridges may be loaded. Many designs using this concept were developed from around 1850-1880 or so. One of the early models was the Treeby Chain gun invented in 1854.

The Treeby Chain Gun, courtesy the Forgotten Weapons Blog. Click on the images to enlarge.

The above images are from the Forgotten Weapons Blog, a wonderful source of information. This weapon is somewhat complex to operate: the user has to rotate the lever on the barrel upwards, which pulls the barrel away from the chamber. Next, the hammer is cocked, which also rotates the chain and brings the next cartridge into the chamber. Then the user rotates the lever back down, which pushes the barrel back against the chamber, thereby sealing it. Now the gun is ready to fire. However, the gun was rejected by the British military for various reasons, one of them being that if the user didn't lock the barrel back before pulling the trigger, bad things could happen. Only two prototypes of this gun were known to have been built.

Over in America, the Josselyn Revolver was patented in 1866 by Henry S. Josselyn.

Public domain image of the Josselyn revolver patent. Click on the image to enlarge.

The details of Henry Josselyn's patent may be found here. A specimen of this revolver is in the Smithsonian museum. Like the Treeby chain gun, the Josselyn revolver didn't sell as well either, possibly because of the inconvenience of carrying one around.

Finally, in 1878, a French civil engineer named Paulin Gay and a French merchant named Henry Guenot patented chain driven firearms, the Guycot pistol and Guycot rifle.

A Guycot pistol. Click on the image to enlarge

A Guycot rifle. Click on the images to enlarge.

The Guycot guns have a chain with cups that can hold centerfire cartridges. The chain is looped through the receiver and the stock. Pulling the trigger revolves the chain and also retracts a firing pin backwards and then releases it to strike the cartridge and fire it. This means that once it is loaded, the gun can be fired as fast as the user can pull the trigger. Paulin Gay reportedly got the idea of using a chain in 1882, after observing chains being used to cut stone blocks in a quarry. Shortly after receiving their French patent in 1878, the inventors also received a British patent in 1879.

The Guycot pistol has a capacity of 40 cartridges and the Guycot rifle can hold 80 cartridges. Compared to their competitors during that era, the Colt revolver (holds 6 cartridges) and the Henry rifle (which can only hold 16 cartridges), the Guycot pistol and rifle have a huge advantage in capacity. However, they never really caught on for some reason either.

There were also other similar chain gun patents from that era.

Mechanism of a "Bicycle chain" gun from a 19th century patent. Click on the image to enlarge. Public domain image.

The above image is from a 19th century patent for a handgun.

In spite of having larger capacities than other firearm types of that era, chain guns didn't sell very well as personal defense weapons because of the inconvenience of the loose belt hanging out of the firearm. However, they are well suited for machine guns, which hadn't been invented yet. In our next post, we will look at some modern chain guns.

In our last post, we studied chain guns from the 19th century. In today's post, we will study modern chain guns.

When we look at firearms throughout history, repeating firearms have been based on two different feed mechanisms:

In the first category, we have manually powered feed mechanisms (i.e.) the firearm is loaded and cocked by the user pulling a lever somewhere on the firearm. In this category, we have mechanisms like bolt action, lever action, pump action etc., as well as revolver mechanisms such as single action revolver, double action revolver etc. Firearms in this category have a firing rate based on how fast a human can manipulate the reloading mechanism and then pull the trigger. In some cases (e.g. double action revolvers), the act of pulling the trigger drives the feed mechanism and also fires the firearm. The firearms in this category are generally older and date from 18th and middle 19th century.
In the second category, we have firearms that use some of the energy from firing a cartridge to drive the feed and firing mechanism. In this category, we have semi-automatic and fully automatic firearms of various types, such as blowback operated, recoil operated, gas operated etc. Firearms in this category are generally from the late 19th century and 20th century and include most pistols and rifles invented in the 20th and 21st centuries. The reloading/feed mechanism operates faster than what a user can accomplish manually and therefore, these firearms have a faster firing rate than firearms in the first category.

Firearms in the second category are very common in the 20th and 21st centuries. However, they generally have one weakness -- if a cartridge is faulty and does not fire properly, then the feed mechanism stops working and the user has to stop shooting until the faulty cartridge is removed. Firearms in the first category don't have this problem -- if a cartridge is bad, the user can usually pull the feed lever again and use the next cartridge in the magazine.

Since the latter part of the 20th century, we can add a third category for repeating firearms: using an externally powered source to drive the feed mechanism. In this category, we have modern chain guns. A chain gun uses an electric motor and a continuous chain to drive the feed and firing mechanisms. The chain is similar to that used in bicycles and motorcycles. Unlike weapons in the second category, a faulty cartridge will not stop the weapon from operating, since the mechanism is driven by external forces and the faulty cartridge will be merely ejected out.

It might be interesting to note that while there are quite a few chain driven guns made by different companies, the words "Chain Gun" are actually a registered trademark owned by Alliant Techsystems Inc.

Hughes EX-34 Chain gun. Click on the image to enlarge.

The above image shows a Hughes EX-34 chain gun and guns based on its operating system are found on helicopters, tanks, armored fighting vehicles etc.

Schematic of the Hughes chain drive system. Click on the image to enlarge.

The above image is from a patent document that shows the mechanism for the Hughes chain driven gun. The chain is powered by an electric motor that runs on 24 to 28 volts. The chain operates the ammunition belt feed, as well as powering the extraction mechanism and the firing mechanism.

MK 38 Machine gun. Public domain image.

The above picture shows the MK 38 machine gun system, which is used on US Navy ships since 1986. It has a range of 2700 meters, fires 25 mm. (1 inch) shells and is used as a defensive weapon to counter fast moving surface targets.

In chain driven weapons, the rate of fire can be adjusted as needed and most chain driven weapons have multiple firing speeds. For instance, the Bushmaster M242 can be fired in single shot, burst and fully automatic modes.

Chain driven mechanisms are generally used for larger caliber guns and auto-cannons and have a correspondingly bigger recoil than hand held firearms. Therefore, most chain guns are usually mounted on a vehicle, such as a ship, helicopter, tank etc.

In our last couple of posts, we studied some different ways that people feed machine guns with ammunition. In today's post, we will study another related way of feeding machine guns that was used by one particular manufacturer. We are talking about feed strips.

Unlike an ammunition belt, a feed strip is a rigid strip of metal upon which cartridges may be placed.

A strip magazine. Click on the image to enlarge.

Image licensed under the Creative Commons Attribution-Share Alike France 2.0 license by rubin16 at wikipedia

The gun has an oscillating arm that feeds a new cartridge into the chamber each time it moves.

Feed strips were mostly used by machine guns made by the Hotchkiss company. It is interesting to note that while the manufacturer, Hotchkiss et Cie, is a French company, it was actually founded by an American, Benjamin Hotchkiss. Mr. Hotchkiss got his start working as a gunsmith in Connecticut, but after the American Civil War, the US government lost interest in funding new types of weapons. Due to this, Mr. Hotchkiss moved to Europe and founded a factory in France. His company produced a revolving cannon and several machine gun models. Many of his machine gun models were built to use strip magazines and were used by the French as well as Allied forces in World War I.

Indian gun crew from the 2nd Rajput light infantry regiment at the battle of Flanders in Belgium. Public domain image.

In the above image, we see a Hotchkiss M1909 machine gun (the Mark-I model) being used by an Indian gun crew in Flanders, Belgium. Note the feed strip sticking out of the gun on one side. As soon as the strip was used up, the gun would lock back and the feed strip would automatically fall out. The loader would then insert the next feed strip on the side and the gun would be back in action again.

The M1909 was followed by the Hotchkiss M1914, which was successfully used by the French military from about 1914 to 1940 or so and also saw service with Americans, Japanese, Russian, Chinese, Greeks etc. While the gun was very effective when used by a three-man crew, the feed strip system was not so effective when used by a single gunner from the inside of a tank.

By the time Hotchkiss came out with the M1922 model, feed strips were falling out of popularity for various reasons. First, feed strips cannot hold as many cartridges as ammunition belts. Different models of feed strips could only hold 15, 24 or 30 cartridges at most. An additional problem with feed strips is that they do not protect the ammunition from the weather or from dirt and they are prone to damage. This is why box magazines were preferred because even though box magazines are heavier than feed strips, they offer protection from dirt and are more durable as well. Therefore, several of the Hotchkiss machine gun models were built with different receivers to use ammunition belts or box magazines, instead of feed strips.

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.

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!

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 a high volume 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 34 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.

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.

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.

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.

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.

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)

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.

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.

Over the years, we've briefly discussed the properties of some of the metals used to construct a firearm (such as here and here). In today's post, we will revisit the topic of metals used in firearm construction in greater detail.

In today's post, we will skip over metals used from a bygone era (e.g.) brass, iron, bronze, gunmetal etc. and restrict ourselves to metals that are used in modern firearms. The main metals and alloys used are: steel, stainless steel and aluminum. Of course, there are different grades of these, such as AISI 4140, AISI 4150 etc. and we will study what all this means in today's post.

Briefly speaking, a metal used for gun barrels should be capable of handling large stresses, because it will experience large amounts of pressure (over 50,000 pounds per square inch or 340,000 kpa for metric speakers). It should be strong and elastic and ideally, it should be easy to machine and somewhat cheap. With that said, let's look at the first of the metal alloys: steel.

Steel is an alloy of iron mixed with other elements. The most important of these "other elements" is carbon. Pure iron is actually a soft metal and the addition of carbon allows the steel to be hardened much more than iron. However, an excess of carbon in the steel makes the steel brittle, so the quantity of it has to be carefully controlled. As we have studied previously, steel consists of crystals and it can exist with different crystalline structures. The shapes of these crystalline structures control the physical properties of the steel (such as hardness, elasticity, melting point etc.), The different crystal structures are sometimes called "phases" and there are several of these, such as ferritic phase, austenitic phase, martensitic phase, ledeburite phase, pearlite phase, cementite phase etc.

Steel Phase Diagram

Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported License by Christopher Dang Ngoc Chan.

Steel can be switched from one phase to another, by heating, adding or removing other elements and controlling the cooling rate. The diagram above shows different steel phases and how it changes from one phase to another one, based on the temperature and carbon content. However, carbon isn't the only element added to iron to make steel, there are also other elements added, which also help to change the properties of steel. For instance, adding nickel and manganese makes steel more elastic, vanadium adds hardness, chromium adds hardness, increases melting temperature and adds corrosion resistance. Adding tungsten keeps the steel from forming cementite and forming martensite instead. Sulfur, nitrogen and phosphorus make the steel more brittle, so these are removed during steel manufacture etc.

In America, the Society of Automotive Engineers (SAE) is responsible for maintaining standards for different grades of steel. Some of these specifications were originally developed by the American Iron and Steel Institute (AISI), but since SAE and AISI were often developing standards for the same materials, they decided to combine their efforts and AISI has turned over maintenance of standards to SAE since 1995. In other countries, there are similar organizations, such as the British Standards Institution (BSI), European Committee for Standardization (EN), Japanese Industrial Standards (JIS), German standards (DIN) etc.

Per the SAE standards, the steel grades are labelled with a four-digit number (such as 1060, 4140, 4150 etc.). The first digit indicates the main alloying element of the steel. For instance 1xxx is carbon steel, 2xxx is Nickel steel, 4xxx is molybdenum steel, 7xxx is tungsten steel etc. The second digit indicates the secondary alloying element(s) in the steel and the last two digits indicate the amount of carbon in hundredths of a percent by weight. For instance, 1060 steel is a steel alloy that only contains carbon and has 0.60% by weight of carbon it it. Similarly, 4140 steel has molybdenum and chromium in it, with about 0.40% by weight of carbon and 4150 steel has molybdenum, chromium and about 0.50% by weight of carbon in it. In reality, there is a little leeway allowed. For instance, according to SAE, the allowed percentages by weight for 4140 steel are: Chromium: 0.8 - 1.1 %, Manganese: 0.75 - 1.0 %, Carbon: 0.380 - 0.430 %, Silicon: 0.15 - 0.30 %, Molybdenum: 0.15 - 0.25 %, Sulfur: up to 0.040 % allowed, Phosphorus: up to 0.035% allowed, Iron: 96.785 - 97.77 %. The standards for 4150 steel are similar to 4140, except that the carbon content allowed is 0.48 - 0.53 % by weight and the iron content is correspondingly reduced to 96.745 - 97.67 %, with all the other elements in the same proportions as 4140 steel.

Other countries have similar standards for steel grades. For instance, in Europe, the EN standard 42CrMo4 steel is about the same specifications as SAE 4140 steel, as are the British standard EN 19, Japanese standard SCM 440, German standard 42CrMo4 etc.

Now why did we mention 4140 and 4150 steels? That's because these are steel grades that are heavily used in the firearms industries to make barrels (they are also used to make gears, axles, connecting rods etc. by the automotive industry). These steels belong to the "chrome-molybdenum" or "chrome-moly" family. While these alloys do contain chromium, it is not as much as the chromium content found in stainless steel and therefore, they have less corrosion resistance compared to stainless steel. However, chrome-moly steels can be surface hardened, where the interior of the piece retains its properties, but the surface is hardened against wear and tear.

The standards for 4140 and 4150 grade steels has been around since about 1920 or so. As we noted a few paragraphs above, the difference between 4140 steel and 4150 steel is the carbon content (about 0.40% for 4140 steel and 0.50% for 4150 steel). So the difference between these two steel alloys is only that 4150 steel has approximately 0.1% more carbon. However, this extra 0.1% makes a big difference in the hardness, heat resistance and resistance to wear of 4150 steel, compared to 4140 steel. It also makes 4150 steel so much harder to machine and therefore increases the cost of manufacturing barrels.

The US military wants their barrels to last longer and work well under automatic fire, therefore they are willing to pay the extra costs associated with 4150 grade steel barrels. When you see barrels labelled "mil-spec", these are likely made of 4150 grade steel. That does not mean 4140 grade steel is bad -- in fact, it works well for civilian applications and does last for a long time as well, which is why you find so many manufacturers making barrels out of 4140 steel.

In the next few posts, we will study other metal alloys used in firearms.

In our last post, we looked at steel alloys commonly used in modern barrels. In today's post, we will continue to look at some more steel alloys used in parts of a modern firearm.

Besides the 4140 and 4150 steels that we looked at in the previous post, some other variants are also used for manufacturing barrels. For instance, adding a small amount of the element vanadium to steel (less than 1%) increases the strength, toughness and heat resistance of steel. An alloy called 41V45 (which is basically a steel with similar elements of 4140 or 4150 steel, but with only 0.45 % carbon content and a little vanadium added) is often used with barrels made using the hammer forging method. 4340 and 4350 steels are also used by some barrel makers, but these steels are more difficult to heat treat properly and therefore the cost of the barrels increases. However, if properly manufactured, a 4340 barrel can be much stronger than a barrel made of 4140 steel.

While the barrel of a firearm has to resist large pressures, it is not the only part of the firearm that is subject to such large forces. Another part that also receives a lot of force is the bolt of a firearm. In the case of the M16 family, the US military selected a steel called Carpenter 158 (also known as "C158" or "Car 158") to be used for manufacturing the bolt. Therefore, any AR15 or M16 bolts that claim to follow military specifications (or "mil-spec" for short) should be made of C158 steel as one of the requirements.

The interesting thing about Carpenter 158 is that it is a proprietary steel alloy and its formula and method of manufacturing are not publicly defined. Therefore, there is no SAE standard for it and the sole manufacturer of this steel is a company called Carpenter Technology in Pennsylvania. They do not manufacture this steel continuously and only do a certain amount of mill runs per year, which means it is not always available. They also only sell this steel in large amounts and require the customer to buy a lot of it at a time. Therefore, only large companies like Colt, FN, Daniel Defense etc. can afford to buy this steel.

However, C158 isn't the only steel alloy used to make bolts. Bear in mind that the US military selected C158 in the 1960s and there have been other (and sometimes better) steel alloys developed since then. For instance, some manufacturers use 9310 or 8620 steels to make bolts. The advantage of these steels is that the standards are defined by SAE and there are many manufacturers of these steels. Therefore, supply is less of a problem. Also, 9310 and 8620 steels can be purchased in small quantities and are therefore suitable for smaller manufacturers who cannot afford to buy large amounts of C158 steel at one time. If machined and heat treated properly afterwards, bolts made of 9310 steel can be even better than C158 steel. Another steel alloy used for bolts by some manufacturers is Aermet 100 (which is also used in the landing gear of jet fighters aboard US aircraft carriers). This is actually another proprietary steel alloy made by Carpenter Technology and is reputed to be far superior to C158 and 9310 steels. However, it requires a double hardening treatment process after machining to reach its full potential. In general, bolts made of 9310 steel are far cheaper than those made of C158 steel and bolts made of Aermet steel are the most expensive. However, bolts for AR15/M16 made of 9310 or Aermet 100 cannot be called "mil-spec" even if they exceed the military standard specifications, since the US military specification says that only C158 steel should be used for the bolt of a M16.

The above mentioned 8620 steel is also used by manufacturers to make bolts for certain rifle models. For instance, it was extensively used in World War II for the M1 Garand rifle. Actually, the original M16 rifles also used bolts made of 8620 steel, but the US military found that the bolts were wearing out after 40,000 - 50,000 shots, which is why they went with C158 steel for the bolt. Still, 8620 steel is used for other parts, for instance, the bolt carrier and the receiver. This is because this steel is suitable for casting, welds very well, has very good machining properties and can be heat-treated to become tough and strong. The M1 Garand and the M14 both use 8620 steel for receivers.

For smaller parts that are not subject to much stress, commonly available carbon steel alloys such as 1020 steel are used. This is used to make small parts, such as the trigger guard, the sights, the rifle sling swivels, smaller pins and screws etc. 1020 steel is commonly available, cheap, easy to weld, flatten, machine, forge and heat treat and can be used for any applications where core strength is not critical.

In our next post, we will look into stainless steel grades used in firearms.

In our last couple of posts, we looked at certain types of steel alloys which are used in firearm construction. In today's post, we will look at another type of steel alloy that was invented in 1912 and used in some firearms: stainless steel.

Stainless steel is a steel alloy that contains a high percentage of chromium (greater than 10.5% by weight). Unlike ordinary carbon steels, it has good resistance against corrosion and rusting. This is because of the high chromium content. What happens is that the chromium at the surface of the object reacts with the oxygen in the air, to form a thin layer of chromium oxide. This chromium oxide layer prevents oxygen from reaching the inner steel and therefore blocks rusting and corrosion. It must be remembered that while stainless steel is rust-resistant, it is not rust-proof.

Fittingly, the invention of stainless steel was actually related to firearms. Harry Brearley, an English chemist was working in Sheffield, England for Brown Firth research labs in 1912, trying to find a new steel that could resist erosion caused by high temperatures of gun barrels. It was already known at that time that adding a little chromium to steel increases the melting point of steel. He was trying to establish precisely, the relationship between melting points and chromium content of various steel samples. As part of this study, he was required to study the microstructure of the various steel alloy samples and to do this, he had to polish and etch the samples first. The standard way to do this was to use a weak solution of nitric acid and alcohol to do the etching, but as Mr. Brearley found, some of the samples were exceptionally resistant to these chemicals. After a bit of investigation, he determined that the high chromium content of these samples was responsible for the exceptional resistance to acid. From this research, a whole new industry of manufacturing stainless steels sprung up around the Sheffield area.

Like chrome-moly steels, there are also different grades of stainless steels and only some grades are used in the manufacture of firearms. For instance, SAE grades 410 and 416 are used for firearms barrels. They are both steel alloys with high chromium content (11.5 - 13.5% for 410 stainless steel and 12-14% for 416 stainless steel). The main difference is that 416 stainless steel contains a bit more sulfur in it, which makes it easier to machine than 410 stainless steel, which makes the barrels cheaper to produce. However, 410 stainless steel retains its toughness better and performs better in freezing conditions. Some companies make custom alloys, such as Crucible Specialty Metals' 416R, which is specially designed for precision steel barrels. Another stainless steel alloy used by some makers is 17-4 PH (PH standing for Precipitation Hardening).

Some of the other parts of the guns are also made of 400 or 300 series of stainless steels. The 300 series is more resistant to corrosion than the 400 series of steels, but cannot be hardened as easily, so it is used for parts that aren't exposed to huge forces.

The advantage of stainless steel alloys over chrome-moly steel alloys is that they are easier to machine and resist heat erosion better. However, they are a bit more expensive and cannot be blued using conventional methods. The US military prefers chrome-moly barrels, but most competitive target shooters prefer stainless steel barrels, because they can be machined more precisely and keep their accuracy longer. This is why the majority of match-grade barrels are made of stainless steel.

Helical Magazines - II: The Evans Rifle

Horizontal Magazines

Turret Magazines

Ammunition Belts

Chain Guns - I

Chain Guns - II

Feed Strips

Machine Guns - General

Early Machine Guns

Light Machine Guns

Heavy Machine Guns - I

Heavy Machine Guns - II

Heavy Machine Guns - III: Modern HMGs

Medium Machine Guns - I

Medium Machine Guns - II

General Purpose Machine Guns

Steam Chests

Metals Used in Firearms - I

Metals Used in Firearms - II

Metals Used in Firearms - III