Thursday, July 24, 2014

Chain Guns - II

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.


Wednesday, July 23, 2014

Chain Guns - I

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.

Friday, July 18, 2014

Ammunition Belts

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 pull the belt in, extract and then 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.

Monday, July 14, 2014

Turret Magazines

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 fire 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 news items and 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.


Tuesday, July 8, 2014

Horizontal Magazines

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 opening at the circular part in the image above) 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 out 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.

Tuesday, July 1, 2014

Helical Magazines - II: The Evans Rifle

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.


Sunday, June 29, 2014

Helical Magazines

In our last article, we studied the rotary magazine. In today's article, we will study a magazine that was invented more recently. Today's object of study will be the helical magazine.

The helical magazine was invented by Michael Miller and Warren Stockton in 1985 and produced by the California Instrumentation Company (later known as "Calico"). Interestingly, the California Instrumentation Company was originally known for manufacturing specialized instrumentation for the petroleum industry, but since they already had experience in tooling and engineering, they didn't have too much trouble manufacturing firearms. By about 1988 or 1989, they had the bugs ironed out and started producing them in quantity, along with firearms designed to use these magazines.

Image from the patent application for the helical magazine. Click on the image to enlarge. Public domain image.

The concept behind the helical magazine is to arrange the cartridges in a helical spiral, as shown by figure 2 above. A drive spring rotates the drive member and pushes the cartridges into the chamber. The figure below shows a cutaway of how the magazine works:

Cutaway of a helical magazine on a Calico firearm. Click on the image to enlarge.

The full patent details for this type of magazine may be viewed here. The nice feature of this type of magazine is that it can hold a lot of cartridges in a pretty compact space.


Unfortunately for Calico, the Federal Assault Weapons ban came into effect in 1994 (and was in effect until 2004). This law stated that no firearms manufacturer could produce magazines with greater than 10 cartridge capacity. Therefore, Calico could not really sell their firearms during this period because their biggest selling point was that the magazine could hold a lot of cartridges. Only after 2004 when the law was changed, could they restart manufacturing their firearms. Calico now offers firearms that have 50 and 100 cartridge capacities.

The idea of a helical magazine was copied by other countries, most notably by Russia, China, Hungary, North Korea etc.. The Russian Bizon submachine gun is one such weapon that uses this concept.

Bizon submachine gun. Click on the image to enlarge.
Image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license by Vitaly Kuzmin

The above image is a Russian Bizon submachine gun. The word Bizon is the Russian word for "Bison". The long cylindrical tube that you see under the barrel in the image above is the helical magazine. It comes in two versions: one is chambered for the 9x18 mm. Makarov cartridge and the other model uses the popular 9x19 mm. Parabellum cartridge. Magazine capacity is 64 cartridges for the Makarov cartridge and 53 cartridges for the Parabellum cartridge. Incidentally, two of the designers of this firearm have very famous parents as well: Viktor Kalashnikov (son of Mikhail Kalashnikov, designer of the AK-47) and Alexi Dragunov (son of Evgeny Dragunov, inventor of the SVD sniper rifle).

Compared to box magazines (which can hold about 30-40 magazines before becoming unwieldy), helical magazines can hold a lot more cartridges in a relatively compact space. However, unlike drum magazines, a helical magazine does not stick out of a firearm so much as to affect the balance and ergonomics. On the other hand, helical magazines have a lot more parts than other magazine types (as you can see by the image of the magazine sub-assembly above), so disassembling one can be complicated. Also, loading and unloading the magazine must be done one round at a time, which means it can take a while to do this.