Differences Between the VZ-58 and the AK

First, I'd like to wish all the readers of this blog a very happy 2015.

Quick, identify the firearm in the image below:

Click on the image to enlarge. Public domain image.

If you said something along the lines of "AK-47" or "AKM", then you're wrong. What you're looking at is the Czechoslovakian vz. 58 rifle. The vz. 58 does resemble an AK-47 or an AKM externally, but there are a lot of differences underneath the hood. We will study more about this rifle in this post.

The name "vz. 58" is actually a contraction of "vzor 58' (i,e. "model 58"). The official full name of this weapon is "7,62 mm samopal vzor 58" (i.e. 7.62 mm. automatic firearm model 58"). The number 58 is because this weapon entered service in the year 1958 (the AK-47 is named similarly -- it first entered service in 1947).

After World War II, the Soviet Union started using the 7.62x39 mm. cartridge for its AK-47 and AKM rifles and insisted that all the Warsaw Pact countries use the same cartridge for standardization. Many of the Warsaw pact countries (Poland, Hungary, Romania etc.) adopted the cartridge as well as the AK rifle for their military forces, but the Czechoslovakians decided to only adopt the cartridge, but use their own rifle technologies. They already had a history of developing firearms for 300 years or so, and the city of Brno was most recently known for developing the precursor to the famous Bren gun of World War II. A designer named Jiri Cermak was assigned to develop the new rifle in Brno in 1956 and the new rifle entered service in 1958.

The new rifle was chambered to use the 7.62x39 mm. cartridge, the same as the AK-47. This is about where the similarity between the two ends. What are some of the major differences?

• Action: The AK-47 (and AKM and the rest of the AK family) uses the long stroke piston system, whereas the vz. 58 uses the short stroke piston system. In the short-stroke system, the piston moves for a very short distance (in the case of a vz. 58, it moves 19 mm. (or about 0.74 inches)), whereupon it is stopped by a projection. The short backward movement of the piston imparts a sharp blow to the bolt-carrier, which separates from the piston and then continues backwards due to momentum. In a long stroke system, the piston and the bolt carrier move backward together. This means that the short stroke piston system has a smaller mass of moving parts, since the bolt-carrier weighs less than the combined bolt-carrier and piston together. Therefore, there is less vibration and balance shift due to the moving parts and the vz. 58 is easier to keep pointed to the target.
• Firing mechanism: The AK-47 uses a traditional rotating hammer mechanism, whereas the vz. 58 is striker fired.
• Safety/Fire selector lever: The easiest way to tell if a rifle is a vz.58 or an AK is by looking at the fire-selector lever. The AK-47 family is famous for its clunky large fire selector lever, which is located on the right side of the weapon above the trigger and is cumbersome to operate. The user needs to take the firing hand off the pistol grip to manipulate an AK fire selector lever. The vz. 58 has a smaller, much more ergonomic selector mechanism and the lever can be manipulated without taking the hand off the pistol grip. The following two pictures show the differences (click on the images to enlarge -- the fire selector levers are enclosed in red ovals in the images below):

AKM fire selector lever. Note the length of the fire selector lever and its position relative to the pistol grip.
Click on the image to enlarge.

vz.58 fire selector lever. Notice how it is positioned close to the pistol grip and can be easily manipulated.
Click on the image to enlarge

• Magazine: The AK-47, AKM and vz. 58 all come with 30 round box magazines, however, the vz. 58 magazine is shaped a bit  differently, so it cannot be inserted into an AK and vice-versa. The vz. 58 magazine is also made of a lightweight aluminum alloy and therefore, it is lighter than the steel magazines of the AK family. The vz. 58 magazine can also be loaded via stripper clips, without removing the magazine from the rifle.
• Receiver: The early AK-47 receivers were made of milled steel, until the Soviets mastered the art of producing stamped steel parts from the Germans and the AKM (and all subsequent AK models) all have stamped steel parts. This was done to improve the production rate. The vz. 58 still uses a milled steel receiver. While it takes longer to make a milled steel receiver, it is more rigid and therefore has a bit more accuracy.
• Lock action: The vz. 58 has a tilting lock action with a falling breechblock (similar to Beretta 92)
• Bolt hold-open feature: When the last round has been fired in a vz. 58, the bolt catch locks the bolt carrier to the rear of the gun and it stays open, which alerts the user that the firearm is empty. In an AK, the majority of the magazines allow the bolt to go forward on an empty magazine, therefore, the user cannot easily tell that the rifle is empty.
• Stock: The early vz. 58s were made using beech wood stocks, but they soon switched to using a wood-impregnated plastic stock. If you click on the image of the rifle above to enlarge it, you'll notice that the stock has a somewhat grainy look to it. These stocks are affectionately known as "beaver barf" to collectors and are light, durable and economical. AK rifles use laminated wood stocks (earlier models used normal wood and later models use plastic), which are also durable and cheap to produce, but they are a bit heavier. Later stocks on vz. 58 were made of steel and alloys and designed to be foldable or collapsible. One more difference is that the stock on a vz. 58 is designed to be modular and easily detachable/interchangeable.
• Dust Cover: The receiver on a vz. 58 has no ejection port dust cover, because the receiver is completely enclosed by the bolt carrier. Therefore, the ejection port is huge compared to an AK. This can be easily seen when the rifle is being operated. 
• Disassembly: The vz. 58 is held by two pins and is designed to be disassembled without using any tools.

Even though the AK family and the vz. 58 look very similar externally, the vz. 58 cannot exchange parts with the AK family because of the vast differences in the mechanisms.

The following video makes the differences between the two very clear.

The vz.58 was manufactured between 1958 and 1984 and around one million rifles were manufactured, which means they are not as widespread as the AK family. They still remain in use with Czech and Slovak military forces, and they were exported to some other countries as well (Cuba, Vietnam, India, Indonesia, Ethiopia, Uganda etc.)

History and Development of the Assault Rifle - X

With the advent of bullpup designs in the 1970s such as the Austrian Steyr AUG and the French FAMAS, some of the newer designs that have emerged since then have largely been bullpup designs. Some of these include the British L85A1 and L85A2 of the 1980s, the Chinese QBZ-95, the German Heckler & Koch G11, Singapore's SAR-21, Israel's Tavor TAR-21 etc.

Since the advent of the 5.56x45 mm. NATO cartridge, the world has essentially gone into three basic calibers as far as militaries are concerned: the NATO 5.56x45 mm. (used by M16, Steyr AUG, FAMAS, L85, INSAS etc.), the Russian 5.45x39 mm. (used by AK74 family) and the Russian 7.62x39 mm. (used by AK-47, AKM and clones such as the Type 56). The first two of these are generally used by most military forces, whereas the third cartridge is generally widespread among many insurgent groups due to the popularity and wide-spread nature of the AK-47 and AKM family of assault rifles. However, there has been some other significant research in cartridge developments as well. Both the UK and the US did some work to find an intermediate cartridge between the NATO 5.56x45 mm. and the older NATO 7.62x51 mm., in order to strike a balance between bullet effectiveness and recoil force. This was due to the 7.62x51 mm. cartridge having too much power and weight and the 5.56x45 mm. not having sufficient range for some applications. Experiments showed that cartridges such as the 6x45 mm., the Grendel 6.5x38 mm. or the Remington SPC 6.8x43 mm. strike a pretty good balance by having more range than a 5.56x45 mm. cartridge, but still having relatively less recoil and less weight than a 7.62x51 mm. cartridge. With combat in Afghanistan taking place over longer ranges and the advent of scopes on assault rifles, it is possible for an infantryman to engage over longer ranges now and hence there have been noises made in various quarters to replace the M16 with a newer rifle using one of these cartridges instead.

Newer bullet designs using exotic technologies were also tried out during the 1970s and 80s, but they've been much less successful in this regard. For instance, there were attempts to design cartridges that fired flechette darts instead of conventional bullets. However, the cost of ammunition was prohibitive and thus this never became popular. Another exotic concept was folded ammunition, which was ammunition that was roughly U-shaped. The idea was to reduce the length of the cartridge in order to speed up the firing cycle of rifles.

Folded ammunition examples. Click on images to enlarge.

Folding ammunition never caught on either. Another concept was the caseless ammunition cartridge, for which a lot of work was done by Hecker & Koch and Dynamit industries. The idea is that since a caseless cartridge doesn't have a brass case, there is no need for the rifle to eject it after every shot, which reduces the number of steps in a firing cycle and thereby enables faster firing rates. H&K developed the G11 assault rifle to use caseless ammunition. The concept of a consumable cartridge is actually a very old one, as it was used by the Dreyse Needle Gun of 1835! However, with automatic weapons and modern ammunition, there are more problems to solve. For one, caseless cartridges are more easily damaged by rough handling since they don't have a hard outer case and two, the brass case removes some of the heat from the chamber of the firearm and the lack of a brass case means that caseless ammunition could cook-off in a hot chamber. H&K solved the first problem by putting cartridges in a sealed plastic case and had to spend a lot of time developing special propellants to solve the second issue. The G11 was about to be adopted by the West German military when the Berlin wall came down and the cold war ended. This resulted in cutbacks in military spending and H&K went into financial difficulties as a result and was acquired by the British, where they earned their keep by helping fix problems with the British L85 assault rifles. Interest in caseless ammunition technology has been renewed since 2004, due to the US military's Lightweight Small Arms Technology (LSAT) program.

Oddly enough, despite most of the new rifles being bullpup layouts, the US military is looking at conventional layouts for their M16 replacements. For instance, the US Army has switched to the M4 (which is the carbine form of the M16). The (now cancelled) XM8 project, which was designed to replace the M16, also had a conventional layout:

XM8 Assault Rifle. Click on image to enlarge. Public domain image.

The FN SCAR, adopted by the US Special Operations Command (SOCOM) as well as the US Marines M27 Infantry Automatic Rifle also use conventional layouts. Thus, it appears that the US is definitely not bucking the bullpup-layout trend, at least in the near future.

Another interesting concept developed in Australia is the Metal Storm rifle, where many bullets are stacked head to tail in series inside a barrel, with propellant between the bullets. Ignition of individual cartridges is accomplished electronically. Since the cartridges are completely consumable and because they are stacked one behind the other in line, there is no need for case ejection or a feed system to load new cartridges in the chamber. This makes the firing rate much faster than other designs, as well as contributing to reduced weight. As of now, Metal Storm products have found limited use and support from the US Marines.

History and Development of the Assault Rifle - IV

In the last post, we studied the origins of the AK-47 and the beginning of the AKM. The AKM featured several improvements over the AK-47, mostly geared towards improving the production rate. In the initial AK-47 design, they had attempted to make the receiver out of stamped parts to speed up production, but the Soviets lacked the proper technology to do so and had issues with the resulting product. Hence, they resorted to machining the receiver from a block of metal, which was a slower process. However, in the 1950s, they used several captured German technicians to teach them metal stamping technology and hence the AKM featured a stamped receiver. Among the many improvements that the AKM had over the original AK-47:

• Replacement of the milled receiver with a receiver made out of stamped sheet steel. Machining is a lot slower process than using a press to stamp parts. Hence, use of stamped parts made it much faster to produce AKMs.
• Using rivets instead of welds on the receiver, in order to speed up production.
• Improvements to barrel, gas ports etc. to speed up manufacturing and enhance reliability
• Weight reduction of approximately 1 kg. (2.2. pounds)
• Retains the chrome lined barrel and chamber of the AK-47 Type-2 variant, but the barrel is pressed and pinned to the receiver, instead of the AK-47 which has a threaded barrel that is screwed into the receiver.
• The barrel is the first in the AK family to have a slant compensator to reduce rifle climb, when shooting in automatic mode.
• Gas relief ports are moved forward to the gas block, instead of the gas tube.
• Bolt carrier was lightened slightly. The wooden stocks were also hollowed out as well, in order to reduce more weight.
• Sights on an AKM are calibrated to go up to 1000 meters, whereas AK-47s are only calibrated to go up to 800 meters.
• Changes to the metal treatment applied. The AKM is parkerized instead of blued like the AK-47.
• Uses modified spring and trigger assembly for better safety. The AKM fires in automatic mode only when the bolt is fully locked. The new trigger assembly also reduces "trigger bounce" and has a hammer release delay device to delay the release of the hammer by a few microseconds in automatic firing mode. The hammer release delay mechanism is sometimes incorrectly called a "rate reducer" by some people, but it doesn't appreciably change the cyclic rate of fire. Instead it allows the bolt group to settle in the forwardmost position after returning into the battery.

The Soviets made millions of AKMs and they weren't shy about handing out the plans to other co-operating countries, so that they could make their own as well. This is why AKMs are so widespread around the world.

AKM assault rifle. Click on image to enlarge. Public domain image.

The basic AKM design also has a number of variants. Some of these are:

• AKMS - This is one of the commoner variants of the base AKM. The AKMS features a metal stock, which is foldable.
• AKMP - This variation uses tritium front and rear sights for better visibility in low light conditions
• AKML - This variant has a side mounting rail to mount a night vision device.
• AKMLP - Same as AKML, but also has tritium sights as a backup.
• AKMSP - Same as AKMS, but fitted with tritium sights
• AKMSN and AKMSNP - Same as AKMS (i.e. foldable stock), but also has a side mounting rail to attach a night vision device. The AKMSNP version also has tritium sights.

History and Development of the Assault Rifle - III

In this post, we will look at the history of one of the most famous assault rifles in history, the AK-47. The AK family is pretty widespread around the world these days, but there are widespread myths about its origins. The Soviet propaganda machine liked to portray that it was an original design entirely invented by a self-taught Russian peasant named Mikhail Kalashnikov. The real truth is actually somewhat different. We will study the history of this firearm in the following series of posts.

In the last post, we saw how the concept of the assault rifle was successfully used by the Germans. Their assault rifle was used against the Soviet Union with great success. The Soviets, in turn, analyzed some captured weapons and decided that it was a pretty good idea. Another major influence was the American M1 Garand rifle, which was also supplied to the Soviets in large quantities by the US and the Soviets decided that they must also have a reliable weapon that fires intermediate power cartridges. They quickly established a factory to manufacture 7.62x41 mm. ammunition, but needed a rifle to go with it. The initial requests for new rifle designs were sent to various Soviet bureaus in late 1943 and by the spring of 1944, at least ten designs were submitted by different groups. The Soviets adopted a design by one Mr. Sudayev and his design was called the AS-44. A limited run of the AS-44 was produced just after WW-II ended and the troops were generally happy with these weapons as they were better than what they had previously. However, the AS-44 was just too heavy and thus the Soviets opened another design competition in 1946.

Meanwhile, in a little known battle, called the Battle of Bryansk in 1942, a certain Russian T34 tank commander named Mikhail Kalashnikov was wounded in combat and made it to the hospital on foot, to receive medical treatment. During his recovery period, he vowed that he would make sure that his country would never be defeated again. While he was lying in bed, he overheard some other soldiers complaining about the quality of the Soviet rifles and his own experiences with the standard Soviet infantry rifles of that period also were similar. Hence, he began to design his own firearm, a sub-machine gun. While his sub-machine gun design was rejected because it was over-complex, his talents as a designer were noticed and he was reassigned to the Red Army's Small Arms Research division. Here, he designed a carbine, which was heavily influenced by the American M1 Garand  rifle's piston driven gas-operated system (if the reader looks at an AK, it uses a gas-operated system almost identical to the Garand, except that the AK has the gas tube mounted on top of the barrel whereas it is below the barrel in an M1 Garand.) While this carbine also was not successful, it was the basis of a new assault rifle that was submitted to the Soviet design competition of 1946, the AK-1 (otherwise known as the AK-46). There were 16 other competing designs originally, with the old AS-44 acting as the benchmark standard and after the first round of trials, the AK-46 was chosen along with entries by A.A. Demetyev (the AD-46 rifle) and F. Bulkin (AB-46 rifle). In the second round of trials, the AK-46 was actually rejected because it did not perform as well as its other rivals, but Mikhail Kalashnikov managed to pull enough strings in the selection committee to continue work on his design and submit a new entry for the next round of trials. He went back to the drawing board with his assistant, Alexandr Zaitsyev, and decided to incorporate design features from other weapons (including some from his competitors, the AB-46 and AD-46!). The design of the AK-46's gas operated systems was already heavily influenced by the M1 Garand and the idea of the long stroke piston attached to the bolt carrier and return spring design were lifted from the AB-46 and the idea of large clearances came from the AS-44 and the safety lever mechanism was from the John Browning designed Remington 8 etc.  The new design was dubbed the AK-47.

The other two designers were also given an opportunity to make design improvements for the next set of trials held in 1947. In the next round of trials, the F. Bulkin design (AB-47/TKB-415) was actually the most accurate of the three weapons and the AK-47 was last.  However, the AB-47 had issues with parts wearing out quickly and the AK-47 beat out the other two handily in tests for durability and reliability. The selection committee made the decision that it is better to have a not-so-accurate-but-durable-and-reliable firearm than wait for an indefinite period for an accurate-and-reliable weapon and hence the AK-47 was chosen over its two competitors. The first version of this was deployed to limited troops between 1947 and 1948.

Initially the design called for a stamped steel receiver pinned at the front, for quicker manufacturing time. However, Soviet machine technology was not advanced enough to do this reliably and there were a large number of rejected receivers. Hence, the decision was made to manufacture the receivers using various machining operations. This made the manufacturing processes slower, but at least they could make reliable receivers this way. Therefore the AK-47 Mark I featured a machined receiver.

Meanwhile, a designer named German A. Korobov began to make an improved assault rifle design himself. Korobov had actually submitted a bullpup assault rifle design (the TKB-408) for the original design competion of 1946, but it was rejected after the first round of testing. Nevertheless, he continued to experiment with other bullpup and traditional rifle designs. By 1952, he switched to using the lever-delayed blowback action invented by Hungarian designer, Paul Kiraly. This led to more accuracy and simpler production for his design. In 1955, the Soviets started another design competition and the improved Korobov design (TKB-517) was submitted to the competition.

Meanwhile, the AK guys were not sitting idle either. They recruited several captured German engineers, including the renowned Hugo Schmeisser (the designer of the StG44) and learned mass production techniques from them. Their new design submission for the 1955 competition was the AKM (AK Modernizirovanniy, the Russian word for "Modernized").

Believe it or not, the TKB-517 pretty much beat the AKM on almost all counts. It was more accurate (especially in full automatic mode), significantly lighter and about 1/3rd cheaper to manufacture. So why did the Soviets adopt the AKM then? Because the selection committee decided that since the troops were already familiar with the AK-47, it would not be a good idea to replace it with a firearm that uses an entirely new design. Hence, the less-reliable, but more familiar AKM beat out the more accurate, but new design, TKB-517.

In the next post, we will look at further developments of the AK-47.

What is the difference between a rifle, SLR, submachine gun, carbine etc.?

A very common question among newbies to firearms history is "What is the difference between a rifle, a sub machine gun, a machine gun, a carbine, SLR, assault rifle etc." This post attempts to point out the differences and name famous weapons of each type.

Rifle: The name "rifle" originally comes from the fact that the barrel of such weapons is "rifled". This means that the barrel has grooves in it to impart spin to the bullet as it comes out of the barrel. This spin helps to stabilize the bullet as it travels through the air and gives it a predictable drift (e.g.) a particular rifle may fire bullets that travel 1-2 cm. to the right every 100 meters on a windless day. This feature allows the user to reasonably predict where a bullet will hit and gives the rifle its accuracy. Earlier firearms, such as muskets, had smooth barrels. Smooth bore weapons were much easier to manufacture than rifles, but lacked in accuracy, as the bullets didn't have stability in the air and deviated in a random direction from the intended target. Therefore, the standard strategy for European armies of that period was to line up men in parallel lines and tell them to all simultaneously open fire at the enemy, because almost no one could reliably hit the enemy that he was actually aiming for. This massed fire strategy worked because some enemy would be hit, even if they weren't the ones that were originally targeted. These days, most modern firearms, even small ones, such as revolvers and pistols, have rifled barrels. Therefore, in modern times, the word "rifle" by itself, implies a firearm that has a rifled barrel, is designed to be fired from the shoulder, is manually fed (i.e. after each shot fired, the user has to manually operate a lever to feed a new cartridge into the weapon) and carries a small number of cartridges internally (say 1 to 5 cartridges). Examples of modern rifles from the early 20th century would be the famous American .30-06 M1903 rifle, the British 0.303 Lee-Enfield, the Mauser M98 etc.

Assault Rifle: In the early part of the 20th century, it was realized by some military forces that most conscripted troops, who were hastily trained in wartime conditions, had less than a 50% chance of hitting a target beyond 300 meters. It was also realized that most infantry encounters occurred at less than 500 meters and rate of firepower was also an important factor in these encounters. It was therefore reasoned that there was no need to give such soldiers a weapon and ammunition capable of hitting targets at 2000+ meter ranges, since most soldiers could not hope to hit a target that far away in the first place. Instead, it was reasoned that it was better to give troops lesser powered (and therefore, smaller and lighter) ammunition to suit the actual ranges that most infantry engagements occurred at and a correspondingly lighter weapon suited to fire this ammunition. With lighter ammunition and weapon, the soldier could carry more ammunition and therefore use a weapon with a higher rate of fire. While the concept was around before World War II, it was the German StG 44 (Sturmgewehr 44) that really popularized the concept. The word Sturmgewehr was coined by Adolf Hitler and literally translates to "Storm Rifle" (the word "storm" being used in the context of "storming a castle" or "assaulting a castle") and the term "assault rifle" is actually a translation of "Sturmgewehr". Even though there were earlier weapons that could be classified as assault rifles, many historians consider the StG 44 as the first to form the concept of modern assault rifles. In these times, an assault rifle is a weapon with the following characteristics:

• Has a rifled barrel (as in the case of the rifle described in the previous section).
• Has provision to be fired from the shoulder, just like a rifle.
• Uses an intermediate powered cartridge. This means that the cartridges are smaller than those used by a regular rifle, but larger than the cartridges used by a pistol. This is one of the key differences between an assault rifle and a regular rifle.
• Is capable of selective fire modes. This means it allows the user to select between firing different numbers of shots each time the trigger is pulled. In semi automatic mode, the weapon will shoot one bullet each time the trigger is pulled. The weapon automatically chambers the next cartridge to fire, but the user needs to let go of the trigger and pull it again to shoot it. In burst mode, the weapon will fire a preset number of cartridges (say 2 or 3) with each trigger pull. In fully automatic mode, the weapon will continue to keep firing as long as the trigger is pulled and there is ammunition. The ability to switch between various modes of fire is a key feature that distinguishes an assault rifle from other types.
• Has a detachable magazine. Most modern assault rifle magazines carry 20 to 30 cartridges or so.

Examples of assault rifles include the AK-47 family, the M16 family etc.

SLR: This is an acronym for "Self Loading Rifle". The term "SLR" is usually used in commonwealth countries. This has some common features with the assault rifle described above. Like the assault rifle, this is also a weapon that has a rifled barrel and is designed to be fired from the shoulder. It also uses an intermediate powered cartridge and has a detachable magazine like the assault rifle concept. The one key difference between assault rifles and SLRs is that SLRs have only one firing mode, the "semi-automatic mode". This means that each time the user pulls the trigger, the weapon will fire only one cartridge. It will automatically eject the fired cartridge, load the next cartridge and prepare the weapon to fire, but the user has to let go of the trigger and then pull it again to fire the next cartridge. This is unlike an assault rifle, which has multiple firing modes and allows the user to switch between them. Examples of SLRs would be weapons like the American AR-15 and the Indian Ishapore 1A1 SLR. The AR-15 is a semi-automatic version of the M16 rifle and the 1A1 is a semi-automatic version of the Belgian FN FAL assault rifle.

Carbine: This is a term used for weapons that are versions of rifles or assault rifles, but with a shorter barrel and lighter weight. Carbines are bigger than pistols, but smaller versions of rifles. In the days of the Wild West, mounted riders preferred a shorter and lighter firearm because these were easier to operate than full sized firearms, when riding. In more modern times, people inside moving vehicles or in close quarter jungle combat, preferred shorter weapons for the same reason. Since carbines have shorter barrels, they lack in accuracy compared to full sized rifles or assault rifles. While they use the same cartridge as their full sized cousins, the shorter barrel also means reduced velocity bullets. Many assault rifles also come in a carbine version. For example, the American M4 (a carbine version of the M16 assault rifle), the Israeli Galil SAR (a carbine version of the Galil assault rifle), Steyr AUG carbine ( based on Steyr AUG assault rifle. The carbine form uses a 16 inch barrel, whereas the assault rifle uses a 20 inch barrel) etc.

Submachine Gun: This is a weapon that shares some similarities with assault rifles, but one key difference is that submachine guns are designed to fire pistol cartridges instead of intermediate cartridges. As a result of this, submachine guns are generally lighter and smaller than assault rifles and are about the same dimensions or smaller than carbines. Since they use pistol ammunition, they also have less recoil and therefore can be fired from either the shoulder, the hip, or even holding it like a pistol. The first weapon to use the term "submachine gun" was the famous Tommy Gun that we studied about earlier. This is a fully automatic weapon that fires .45 ACP cartridges, the same cartridge used by the Colt M1911 pistol. Another famous submachine gun from the World War II era is the British Sten gun, which is also a fully automatic weapon. Modern submachine guns such as the Heckler and Koch MP-5 are capable of selecting multiple firing modes. Submachine guns are more preferred for close-range combat in urban environments because, with lower powered pistol cartridges, there is less risk of bullets penetrating through walls and hitting innocents on the other side

Machine Gun: This generally denotes a weapon that is capable of rapid, fully automatic fire and carries a large supply of ammunition. Fully automatic fire means that the weapon will keep firing as long as the trigger is pulled and there is a supply of ammunition available to it. Most machine guns fire either full sized or intermediate sized ammunition, similar to rifles and assault rifles. Machine guns generally carry a large supply of ammunition in ammunition belts, drum magazines or box magazines. This means that they generally have hundreds of cartridges available to them, unlike the 20-30 cartridge magazines used by assault rifles. They are also generally heavier than rifles and assault rifles. Examples of machine guns would be the Gatling Gun, the Gardner Gun, the Bira gun etc. Modern machine guns include the Browning Automatic Rifle (BAR), the British Bren gun, the American Stoner 63, the Belgian FN Minimi etc.

Shooting: Compensators and Muzzle Brakes

When shooting a firearm, one may notice that there is a tendency for the muzzle to rise up in the air after the shot is fired. This effect is called muzzle climb or muzzle rise. The cause of this is basic physics. Look at the two images below:

When a firearm is discharged, there are multiple forces acting upon it. The gases generated by the burning propellant of the cartridge, pushes the bullet out the barrel and also pushes back on the firearm. This force acts on the centerline axis of the barrel. Let this force be represented by A in the two diagrams above. Now, the user of the firearm is also resisting the kick, by holding the firearm with his hands. Let these forces be represented by B in the diagrams above. Note that for the assault rifle, there are two points where force B acts upon (i.e.) at the stock and at the grip. Also note that in both diagrams, force A is acting at a higher point than force B. This causes the rotational torque C, which causes the front of the firearm to rise.

This effect is more visible for heavier caliber weapons or when multiple shots are fired rapidly. There must be some way to prevent this muzzle climb for happening, because no one wants their weapon to act as though it is on anti-aircraft duty, when they're trying to shoot at a target on the ground!

One way to reduce this effect is if A and B are in the same axis (or fairly close to the same height), then the torque C is minimized. Another way to reduce this is to use devices such as a compensator or a muzzle brake.

Public domain image. Click on image to enlarge

In the above picture, we observe that the gentleman in the front of the picture is firing an AKM assault rifle. Notice that the tip of the barrel has a slanted tip and is slightly tilted to the right as well (it is more visible in the enlarged image). This slanted tip is not due to wear and tear or poor maintenance of the weapon -- it is actually a feature. That device is called a slant compensator. What it does is direct some of the escaping gases upwards, thereby pushing the muzzle down. This counteracts the torque trying to push the muzzle up and thereby makes it easier to keep the weapon pointed at the target. The AKM also has a tendency to move to the right, which is why the compensator is also slightly tilted that way, so that it pushes the muzzle to the left to counteract that movement as well. When the Russians decided to make an improved AK-47 version (the AKM), this was one of the standard features added to the AKM model. This simple device could also be retrofitted to older AK-47 models, simply by screwing on this device to the tip of the barrel.

Another device that is similar is called a muzzle brake. Basically, this consists of a small tube that has a number of perforations along its sides, which is attached to the end of the muzzle. These perforations allow the gases to escape at an angle to the muzzle, which not only helps reduce the muzzle climb, but also reduces the recoil felt at the back of the weapon.

Muzzle brake at the tip of an M16 assault rifle.

Yet another way to reduce recoil is called porting. Basically, this involves drilling precise holes near the end of the barrel, which allows some of the gases behind the bullet to escape upwards as the bullet is exiting the barrel, thereby pushing the barrel down.

Public domain image. Springfield Armory XD-40 pistol with ported barrel.

The advantage of such devices is that they reduce muzzle climb as well as felt recoil. This improves the accuracy of the user. It also reduces the load felt by the user during long shooting sessions.

There are also a few disadvantages of such devices. One is that the noise level of the weapon increases by a few decibels. They also increase the flash seen at the end of the barrel. Some muzzle brakes redirect some of the gases towards the user to reduce recoil, but this could cause some of the pressure wave to be redirected to the user as well as extra noise and flash, thereby causing some discomfort. Additionally, if the shooter is firing from a prone position, the redirected gases could throw up some extra dust towards the shooter, which could impair visibility and give away the user's position. Finally, the extra weight at the tip could affect the overall balance and handling of the weapon.

Actions: Blowback Action: Lever Delayed Blowback

In our last couple of posts, we've studied the basic principles of a blowback action and the reason why we want to delay the blowback action. In our last post, we saw that mechanical means can be used to delay the movement of the bolt, by putting it at a mechanical disadvantage by using a couple of rollers (i.e.) the roller delayed blowback action. Another way to achieve the same effect is called a lever-delayed blowback action, which we will study in this post.

When we think of the words "mechanical advantage", the first object that many of us think about is the simple lever. We use a straight rod as a lever, balance it about a fixed pivot (fulcrum) and place the heavy object under the short-end of the lever. We then pull on the long end of the lever. Since we're pulling on the long end, we don't have to apply as much force, but we have to move the lever through a longer distance to move the object a short distance.

Conversely, if we put the object on the long end of the lever and push down down the short end, we put ourselves at a mechanical disadvantage and need to apply a lot more force to move an object. However, pushing down a small distance on the short end will move the object a lot more on the long end.

This is the principle of the lever-delayed blowback action.

Click on image to enlarge and view the animation in all its glory. 

The original image disappeared from the web around May 2013. Luckily I was able to restore it from backup.

In the above image, we have a pretty good animation of how the lever-delayed action works. When the cartridge is fired, the rear movement of the spent cartridge case (the yellow part) acts upon the blue bolt. Before the bolt can move much though, the gray lever rotates and moves the red bolt carrier first, which moves a long way for the short movement of the bolt (the leverage principle we just talked about above). This leverage acting on the bolt carrier increases the force of resistance to movement and slows down the movement of the bolt itself. Once the lever has reached an approximately horizontal position, it ceases to act as a lever and the bolt and the bolt carrier move backwards together at the same speed and are followed by the empty fired cartridge case as well. This extra initial delay in the movement of the bolt serves to keep the gas seal fairly tight until the bullet has left the front end of the barrel and most of the high pressure gases have also gone out the front.

The picture above shows the drawing of an actual weapon (a French FAMAS assault rifle) that uses the lever delayed blowback action. Initially, the cartridge J is in the breech and the hammer H is cocked. When the trigger is pulled, the hammer H releases and strikes the back of the bolt A and the long firing pin E, which strikes the base of the cartridge J, igniting its primer and burning its propellant material. As the bullet begins to leave the front of the barrel, the empty cartridge case J now pushes back on the bolt A, which in turn transmits the force to lever B. The lever B rotates about the pivot C and moves the bolt carrier D faster than the bolt A. Due to this leverage being applied to weight of D, extra force must be applied to A initially to move it. As long as B is rotating, bolt A moves backwards a lot slower than D and therefore the breech stays practically shut. Once B has reached a horizontal position, it ceases to act as a lever and then both A and D move backwards at the same rapid speed, opening the breech. The case J also follows A backwards and is ejected out of a side port due to a spring inside the magazine that is pushing new cartridges upwards. The backward movement of A also compresses a recoil spring in the tube G and also cocks hammer H on the way back. The sear spring mechanism F holds down the hammer H after it is cocked and while the bolt is moving backwards. The bolt moves backwards, continuing to compress the spring G, until it is slowed down to a stop by G and the additional lever and spring K at the back of the weapon. These two then push the bolt forward whereupon it picks up the new cartridge from the magazine and moves it forward into the chamber.

Since this action uses the principle of leverage between A and D, the weights of A and D can be relatively light, since the leverage is what provides the resistance to backward movement of the bolt. This means the weapon can be much lighter than one that is using a straight blowback action. Conversely, the weight savings gained from the lighter action can be re-used to make a heavier barrel and chamber and therefore it can fire a much more powerful cartridge than a straight blowback weapon.

The first lever-delayed blowback action was invented by the famous Danish born US firearms designer, John Pedersen. However, it was perfected by the noted Hungarian firearms designer Paul Kiraly in the 1930s. This action is not used in many weapons, but the most famous current user of this action is the French FAMAS assault rifle.

French FAMAS F1 assault rifle

The FAMAS itself was heavily influenced by the mechanism of the French AA-52 LMG, which was developed after the 1950s and also uses a lever delayed blowback action. The FAMAS is significantly lighter than most assault rifle weapons of its class. Other users of this action include the Dominican Republic San Cristobal 0.30 carbine (designed by Paul Kiraly after he fled Hungary during the communist revolution and settled in the Dominican republic) Brazilian BSM/9 M1 submachine gun, the Italian Benelli B76 pistol and a series of Russian firearms designed by Anatoly Baryshev (AB-7.62, AVB-7.62, LCZ B20).

As an interesting side note, there was also a Soviet assault rifle called the TKB-517 that was developed in the 1950s by a Russian firearms designer named German A. Korobov. Mr. Korobov initially experimented with various assault rifle designs using gas delayed blowback operation throughout the late 1940s. While his earlier attempts were accurate enough, they were not as reliable and therefore, he switched to using a Paul Kiraly designed lever delayed action in 1952, which gave him better accuracy as well as better reliability. In the mid 1950s, the Soviet military decided that they needed to replace the original AK-47 assault rifle with a better design and opened a competition to develop a replacement. The TKB-517 rifle was submitted to the competition against a modified Kalashnikov AK-47 and some other competing designs. The TKB-517 was found to be the most accurate and controllable of all the designs submitted, especially in fully automatic fire mode. It was also much lighter and cheaper to manufacture than even the modified AK, which is quite an achievement in itself. However, the Soviet military decided that the less accurate, more expensive, but familiar and already well established Kalashnikov design was preferable to the more accurate, cheaper, lighter, but newer design TKB-517 and hence, the winner of the competition was declared to be the Kalashnikov designed modified AK, the AKM, which is the most widespread assault rifle in history.