M16 Operation and Functioning Cycle

In our last post, we studied the similarities and differences between the AR-15 and M16 trigger mechanisms. Today's post will be another educational movie courtesy of the US Army (your tax dollars at work!). We will study the methods of operating a M16 rifle and its functioning cycle.

Today's movie was produced sometime in the early 1960s and describes the operation of the M16 rifle, specifically the earlier models. It also shows the functioning cycle of operation of a M16 rifle (i.e.) Firing, Unlocking, Extracting, Ejecting, Cocking, Feeding, Chambering and Locking and describes in detail how each stage works.

Note that this movie is pretty old, it actually refers to the rifle as the XM16E1. This is the first model of the M16 family that was adopted by the US Army. The earlier M16 rifle model was first adopted by the US Air Force, but the US Army insisted on a forward assist lever to be added to the rifle and therefore, the Air Force model was called M16 and the US Army version was called XM16E1 and later renamed to the M16A1 model in 1967. Also, in the early days, M16 magazines only held 20 cartridges and this can be seen in the movie as well.

Happy viewing.

Trigger Mechanisms of the AR-15 and the M16

A little while back, we studied how the trigger mechanisms of the AR-15 and M16 rifles work, complete with a video with animation explaining the concepts.

In today's post, we will look at a couple of videos that show the actual parts, instead of a 3-D Solidworks animation.

First up, an explanation of the AR-15 trigger mechanism:

Next, we have another video, that discusses the trigger mechanism of a M16 and compares it to that of an AR-15

Note that the M16 trigger mechanism being discussed is the M16-A1 model, which is capable of firing in semi-auto (single shot) and full-auto modes (unlike the M16-A2 and A4 models, which can fire in semi-auto and 3-round burst modes only). The AR-15 is capable of semi-auto fire only.

Happy viewing.

The M16 Family - II

In our last post, we looked at some members of the M16 family. We also mentioned that the M16A2 model is a very influential model in the M16 family and is still in use in various military forces. We will continue to look at other members of the M16 family in this post.

M16A4: This rifle is the fourth generation rifle in the M16 series. One of the main differences between this model and the models we've have already studied so far is that the carrying handle on this model is detachable. What the designers did was put picatinny rails on the rifle and also on the hand guards. The carrying handle is attached to the picatinny rail on top and can be removed and replaced with other accessories, such as a reflex sight, night vision device etc. In addition, other accessories may also be attached to the other rail mounts, such as a laser, vertical grip, flash light etc.

The M16A4 rifle. Click on image to enlarge. Public Domain Image.

In the above image, note that the carrying handle has been replaced by a telescopic sight called an ACOG (Advanced Combat Optical Gunsight) and the rifle has an additional vertical grip attached to the hand guard in front. The M16A4 has the same firing modes as the M16A2 (i.e. single shot and 3 round burst) and also retains a bunch of other features from it.

The US Marines were the first to adopt this rifle model and are in the process of phasing out their existing M16A2 rifles with the M16A4. It is also used by some other countries' military forces around the world, such as Thailand, Turkey etc.

M4 Carbine: During the Vietnam war, Colt developed a carbine version of the M16A1, called the CAR-15. Around 1988, there came a need for another carbine design and Colt based it off the influential M16A2 design. The M4 carbine features a shorter 14.5 inch barrel and a telescoping stock. Therefore, it is more compact than the M16A2. It also borrows from the M16A4, by incorporating the rails and the detachable carrying handle, therefore allowing it to accept a wide variety of accessories.

US Soldier carrying a M4 with accessories attached. Click on image to enlarge. Public domain image

Due to its shortened barrel, the ballistic performance of the bullets is slightly worse than the M16A2. However, the smaller length makes it more suitable for close quarter battle. The M4 carbine was first selected for use in 1994, by the US Army, initially to replace the M9 pistol and the M3/M3A1 submachine gun. Later on, they began to replace the M16A2 rifles as well and the US Marines also adopted it for use by officers. Other branches of the military started using it as well and it is also used by other countries around the world.

One variant of the M4 is the M4A1 carbine, which is used by US Special Operations units, such as the Navy SEALs, Army Special Forces, Marines Force Recon, USAF Para-rescue etc. The difference is that while the M4 is capable of single shot and three round burst firing modes, the M4A1 is capable of single shot and fully automatic firing modes.

AR-15: The original prototype of the first M16 model was called the AR-15 (after the company Armalite, which was the original designer of this rifle family). However, after Colt bought the design, they called their model the M16 and made a civilian model of the design in 1963, which they named the AR-15. In this discussion, we will only talk about the civilian models released by Colt and other manufacturers, as few examples of the original Armalite design exist. The AR-15 was designed for civilian sales and while it does have a resemblance to other members of the M16 family, there are some very significant differences. The first major difference is that the AR-15 only has one firing mode (semiautomatic mode, which means you have to pull the trigger each time to shoot a new cartridge). Therefore, it is NOT an assault rifle, since it is incapable of switching firing modes. While the external appearance of an AR-15 is almost identical to a fully automatic M16 family model, the internals are very different. The hammer and trigger are of a different design and the bolt carrier and lower receiver are differently shaped that they cannot be interchanged with a M16 mechanism. This is done to satisfy United States firearm laws that semi-automatic weapons cannot be easily converted to fully-automatic weapons.

Colt AR-15 A3 Carbine Model. Click on image to enlarge.

There are multiple models of AR-15, resembling various other variants of the M16 family. While Colt officially holds the trademark to the term "AR-15", clones are made by many other manufacturers and they are unofficially all referred to as "AR-15". Many of these clones are designed to fire other calibers of ammunition, ranging from small pistol cartridges, to many different rifle calibers and even shotgun shells.

These are only some of the popular variants of the M16 family. There are other international variants that we will study in our next post.

The M16 Family - I

Many months ago, we had explored the differences between various members of the AK family (e.g.) AK-47, AKM, AK-74, AK-101 etc. In today's post, we will explore some of the popular members of the M16 family and discuss the differences between them. We will study the differences in multiple posts, as there are quite a few variants with major differences.

M16: This is the first operational version of the rifle and was only adopted by the US Air Force initially. Among its distinctive features are a triangular shaped forward hand guard, no cleaning compartment in the stock (as Colt famously declared that this rifle was so advanced that it didn't need one), no forward assist lever and a duckbill shaped flash suppressor at the muzzle. The original version was issued with a 20 round magazine. It is capable of selecting firing modes and can fire in single-shot as well as fully automatic modes. The barrel has a rifling twist of 1 turn in 12 inches.

Original M16 rifle. Click on image to enlarge. Public domain image.

In the above image, we see an original M16 rifle. This variant was adopted by the US Air Force, which continued to use this model until 2001 before switching to the M16A2 variant. It was also used by some other military forces, notably the British SAS.

M16A1: This is the variant that was first accepted by the US Army. Soon after the original M16 was ordered by the US Air Force, the Army got in the act and asked for a model with a few changes to it, notably, the addition of a forward assist lever, in case the cartridge did not properly seat in the chamber. Colt and the US Air Force believed that this change was unnecessary, over-complicated the weapon and increased its cost by $4.50. Hence, the Air Force got the M16 variant and the Army got the M16A1 variant., which has the forward assist lever. One more difference is that the duckbill flash suppressor was found to pick up twigs and leaves in jungle conditions and was replaced by a bird-cage style flash suppressor. This variant retains the same triangular forward hand guards, selectable firing modes (single-shot and fully automatic) and rifling twist of the original M16.

The M16A1 rifle. Note the bird-cage flash hider in front of the muzzle and the presence of a forward assist lever.

Early versions of the M16A1 were issued with no cleaning kits and without a chrome lined chamber. This led to a number of jamming issues early on and investigations were made to determine why this was happening. A change in the ammunition formula was found to be the cause, as the new ammunition left more residue in the rifle. Since the rifle was issued without a cleaning kit, soldiers could not properly maintain their weapons and this led to jamming problems in the field. Immediately after the cause was determined, the rifle was changed to include a cleaning kit, stored in a compartment in the stock. The barrel. bolt and chamber were also chromed to resist corrosion. In 1970, the magazine was changed from 20 round capacity to a 30 round capacity, as can be seen in the image above.

After its initial reliability problems were solved, the M16A1 variant became adopted by the US Army and the Marines, as well as other military forces around the world, such as Argentina, Australia, Thailand etc. It is still used by some military forces.

M16A2: This is a very influential version of the M16 family and has a number of differences from the M16A1. Most of the changes were added because of the US Marines. The Marines found that in the Vietnam war, many inexperienced men would put the rifle into fully automatic mode and end up emptying their magazines into the bushes without hitting a single enemy. Hence, they asked for the automatic firing mode to be removed and a three-round burst mode to be added instead. This makes the M16A2 variant capable of firing in single-shot and three round bursts only. Also, NATO forces wanted to use a more powerful version of the 5.56x45 mm. cartridge (the SS109 cartridge). However, the newer cartridge needed the rifling twist of the barrel to be changed, in order to maintain bullet stability in the air. Hence, the M16A2 features a barrel with a twist rate of 1 turn in 7 inches (compared to 1 turn in 12 inches for the earlier models) to work with NATO standard cartridges. The barrel thickness was also increased as the US Marines wanted a stronger barrel to resist bending in the field and not overheat as quickly.

The M16A2 rifle. Click on image to enlarge. Public domain image.

There are also many other major changes. For instance, the material of the buttstock plastic is different and 10 times stronger than the original. The shape of the forward hand guards is round instead of triangular and the two handguard pieces are symmetrical (meaning that either half can fit as the left or right side hand guard). This enables the rifle to be held more easily by smaller hands and the symmetrical hand guards make production easier, as there is no longer a need to manufacture separate left-side and right-side hand guards. The shape of the pistol grip is also different - this version has a notch added to support the middle finger and it has more texture to enhance the grip. Because this rifle is designed to fire the NATO SS109 cartridge, the rear sights are also changed to match this new cartridge's ballistics. Also, the flash suppressor is modified and closed at the bottom, so that it will not kick up dust or snow when fired from the prone position.

This variant was initially adopted by the US Marines and then by the US Army, followed by the other branches of the US military and other military forces around the world. It is still being used by many military forces around the world.

M16A3: This is a variant of the M16A2 model that came out at around the same time as the M16A2. It was produced in small quantities and designed for US Navy SEALS and the Seabee units. The main difference is that while the M16A2 can only fire in single-shot and three-round bursts, the M16A3 can fire in single-shot and fully automatic modes. Special forces are trained to not waste ammunition and hence, this variant allows fully automatic fire.

In the next post, we will study some more variants of the M16 family.

Why does a M16 have Tall Sights?

When we look at an M16 rifle (or its semi-automatic only civilian cousin, the AR-15), there is something noticeable about their sights:

A M16A2 and two M16A4s. Click on images to enlarge. Public domain images.

In all these examples, note that the sights are a good 2.5 inches from the top of the barrel. Why is this the case with the M16 family? We will study the reason in this post.

The first thing to notice in the M16 family of firearms is that the stock is in line with the center of the barrel. In most other rifles, the stock is a little below the line of the barrel and they have small sights mounted on top:

Click on images to enlarge. Public domain images.

The reason why the stock is below the barrel is for ergonomics. When the user rests his/her cheek on the comb of the stock. the user's eye is aligned just above the top of the barrel and therefore the sights can be placed right above the top of the barrel for such firearms.

However, for such stocks, when a bullet is fired, the recoil pushes back in the line of the barrel and the resistance offered by the user's shoulder is below the line of the barrel and this creates a rotational torque. We studied this effect when reading up on muzzle brakes and compensators earlier:

Here, A is the force acting because of the recoil and B is the force resisting the movement from the user's hand and shoulder on the grip and stock. Since A is higher than B, this causes the rotational torque C, which causes the front of the barrel to rise when shooting. This can cause a loss in accuracy, especially when firing rapidly.

In the M16 family of rifles, the rotational torque is minimized by placing the stock higher, so that forces A and B are around the same line with each other. This is called a "straight line layout" and is done in order to make the rifle easier to control, especially when firing in burst fire or automatic fire modes. One more nice feature of the straight line layout is that it allows the operating rod and buffer to run directly back into the stock and thus reduces the overall length of the rifle. However, with a straight line layout, the user cannot comfortably aim the rifle if the sights are just above the line of the barrel. Hence, the solution was to make the sights taller on the M16 family, so that the user can place their cheek on  the stock and still look through the sights comfortably.

By the way, the M16 isn't the only rifle that does this. The German FG42 and MG42 and the US M60 are three earlier examples that have tall sights as well:

FG42 and M60 machine guns. Click on images to enlarge. Public domain images.

In the above images, note that they all have a straight line layout. The FG42 was one of the first firearms to have this feature and came out during World War II. The straight line layout was later adopted by others, such as the M16 family, the Russian Dragunov rifle, the German Heckler and Koch HK36 and XM8, the Swiss SIG SG 510 etc.

A Swiss SIG SG 510. Click on image to enlarge. 

Licensed by user Rama under the Creative Commons Attribution-Share Alike 2.0 France license from wikipedia.org

With taller sights, the user can rest his/her cheek on the comb of the stock as usual and still aim comfortably through the sights. This is why all rifles with straight line layouts have taller sights.

What is a STANAG magazine?

In our last article, we looked at what the deal about teflon-coated bullets was about. In this next post, we will look into STANAG magazines. So what's the big deal about STANAG magazines and why are they called that anyway? This article aims to clear all that up.

Two STANAG compatible magazines. Left is a 20 round magazine made by Colt, right is a 30 round "High Reliablility" magazine made by Heckler & Koch/

Click on image to enlarge.

Image licensed under GNU Free Documentation License v 1.2 or later, by user Raygun on wikipedia.

Back when NATO was first formed, they agreed to develop a set of common standards that all the member countries could use, in order to ensure that the various countries under the NATO umbrella could share arms and ammunition. These standards were called STANdardization AGreements, or STANAGs for short and many were published for various military hardware. We start our story in 1980, soon after NATO had standardized on using the NATO 5.56x45 mm. cartridge for their assault rifles. STANAG 4172 was the document that specified the standards for the NATO 5.56x45 mm. cartridge.  Soon after this, STANAG 4179 was proposed, which described the standards for how the magazines were to be made. Now for the real amusing part: STANAG 4179 was a document containing a proposed standard for magazines, but was never officially accepted by all the member countries and therefore remains as a "Draft STANAG" to this date! Therefore, calling these magazines as "STANAG compatible magazine" is not technically correct.

Nevertheless, many manufacturers started making magazines to the standards proposed by the document, even before it was officially ratified. Some people are under the impression that the STANAG standard specifies the magazine capacity, along with the dimensions of the magazine, but this is an incorrect assumption to make. Even though most of the magazines made for military purposes are usually 20 or 30 round capacity, there exist other STANAG compatible magazines that hold 40, 50 or even 100 rounds. The shape can be different as well, as there are drum magazines and box magazines that are both STANAG compatible. The STANAG 4179 document only specifies some of the dimensions of the magazine and also doesn't specify the materials to be used or manufacturing standards. Therefore, different manufacturers can make the magazines to any length, with different kinds of material (e.g. aluminium, steel, plastic etc.), and still claim to be STANAG compatible. This causes production quality from various manufacturers to differ.

There are now many rifles that can take STANAG magazines, such as AR-15, M-16, Heckler and Koch G41, FAMAS G2, Tavor TAR-21 etc. and some other rifle models such as SIG 556, H&K G36, IMI Galil etc. can also use them with a magazine adapter.

History and Development of the Assault Rifle - VII

In our last post, we studied how the AR-15 rifle was morphed into the M16 A1 model. Where we last left off was during the Vietnam war.

The original design for the M16 had a number of flaws: lack of cleaning kit, no chrome lining on the inside of the barrel or chamber, issues with cartridges etc. These flaws became more evident during the Vietnam war, but sadly, only after a number of US servicemen lost their lives. Soon after a Congressional investigation, fixes were made for all these issues and the rifle became a much more reliable product. However, the bad reputation earned by its early flaws took a lot longer to clear.

By 1970 though, the M16's reputation was established and other countries also wanted their own M16 style rifles. The NATO member countries decided to standardize on the 5.56x45 mm. cartridge, which was also used by the M16 A1 model, but they wanted to make improvements to the US version of the cartridge, in particular, because of improvements to body armor technology. The US version of the 5.56x45 mm. cartridge was called the M193 and tests had shown that it didn't penetrate newer body armors that well. The British, Germans and Belgians all presented cartridges that all had the same 5.56x45 mm. external dimensions, but had different bullet shapes and materials that offered much better ballistics and penetrating power than the M193. In the end, the Belgian designed SS109 (which has a bullet with a steel tip) was chosen as the NATO standard. The Belgians also designed a tracer round, L110, which had better performance than the old M196 tracer round. The M196 could burn out in 450 meters, whereas the L110 could show its trail to 800 meters. However, it was found that the M16 A1's barrel rifling twist rate of 1/12 inch (i.e. 1 turn every 12 inches or 1 turn every 300 mm.) was not adequate to stabilize the SS109 or L110 bullets past about 90 meters or so. New barrels with a faster twist rate were required to get the best performance out of the SS109. The ideal rate for a bullet from a SS109 cartridge is at least 1 turn in 9 inches (1 turn in 229 mm.), but the L110 requires at least 1 turn in 7 inches (1 turn in 180 mm.) to continue to be stable for much longer ranges (over 800 meters or so). Hence, it was decided to make a new version of the M16, the model A2, which would feature a barrel with a 1 turn in 7 inch twist rate.

It was also found during the Vietnam war, that many soldiers would put their M16s into full-automatic mode and when in a firefight, new soldiers would often hold down the trigger and shoot entire magazines into the bushes in a few seconds, without killing a single enemy. This caused many of them to run out of ammunition prematurely. Also, the act of firing in full-automatic mode makes the rifle more difficult to control and thereby reduces accuracy. The US military conducted various tests a decided to replace the full-automatic firing mode with a three-round burst mode (i.e. upto 3 rounds would fire when the trigger is held down), because the three-round burst was determined to be the optimum balance between accuracy, ammunition conservation and firepower. The US Marines were the first to request the development of the M16A2 model based on the Vietnam war experiences.

M16A2 model. Click on image to enlarge. Public domain image.

Along with the newer barrel with the 1:7 inch twist rate and the three-round burst mode, there were numerous other improvements made to the M16A2. The thickness of the barrel in front of the front sight was made thicker, to avoid bending the barrel in the field and to also resist overheating better, thereby allowing firing the weapon for longer periods of time. The front and rear sights were improved and the rear sight was made adjustable for ranges between 300-800 meters using the SS109 cartridge (which had different ballistics than the M193). The recoil compensator at the end of the barrel was closed at the bottom, so it would not kick up dust when fired in the prone position. A deflector was attached immediately behind the ejection port, so that left handed users would not get hit in the face by a hot ejected case. The grips were improved and the handguards were made symmetrical so that there was no need to manufacture spare parts for left and right side. With advances made in polymers, the buttstock was re-engineered to use a new plastic that is 10 times stronger than the original stock on the M16A1. The buttstock was also made slightly longer than the original version.

The M16A2 model was first adopted by the US Marine Corps in 1982, followed by the US Army in 1986 and then the other branches of the US military, as well as military forces of other countries worldwide. It is still being used by many users and is the most common variant in the M16 family.

The M16A3 model came out around the same time as the M16A2, but was made in very small numbers indeed. The M16A3 is very similar to the M16A2, but retains the original full-automatic firing mode of the M16A1 instead of the three-round burst mode of the M16A2. This variant was made for US Special Forces, who need the extra firepower afforded by the full-automatic firing mode. Special forces personnel are trained to maintain better fire discipline and not use up their ammunition so quickly. The US Navy was the first to order this variant, for use by its SEAL and Seabee units.

The M16A4 and the M4 are the latest variants of the M16 family.

M16A4 rifles. Click on image to enlarge. Public domain image.

The M16A4 is currently being issued to US Marine Corps front line units, and some US Army units. The main difference between this and the M16A2 is the removal of the fixed carrying handle/rear sight, which is seen on the M16A2. Instead, this is replaced by a Picatinny rail on the A4 model. This allows the user to not only attach a carrying handle, but also other accessories, such as a scope, as seen in the image above. The hand guards in front of the magazine are also of a new design (Knight Armament's M5 RAS handguard), which allows the user to attach a vertical grip, tactical light, laser sight etc.

The M4 variant is a carbine firearm and is a shorter and lighter version of the M16A2. It is intended to replace the M16 in most units of the US Army.

The M16 rifle had initial teething issues, but has later evolved into a fine, reliable weapon, which is in use by several military forces around the world.

History and Development of the Assault Rifle - VI

In our last post, we studied some of the history of the M16's predecessor, the AR-15. Where we left off was right at the end of development of the AR-15 by the Armalite Corporation. At this point, Armalite's parent company, Fairchild Aviation, decided that it had spent too much money on development expenses and wanted to get out of the firearms business. Hence, they sold the production rights to the Colt Firearms Company in December 1959, for $75,000 cash and 4.5% royalty on every unit manufactured. Shortly after this, Eugene Stoner left Armalite and began to work as a consultant for Colt.

Meanwhile, an USAF General, Curtis LeMay, witnessed a demonstration of the AR-15 in mid 1960 and became a proponent of the new weapon. Therefore, in 1961, he requested an order of 80,000 units for use by the Air Force. At that time, the US military was generally using the M14 rifle which fires a 7.62x51 mm. NATO cartridge. Hence, President John F. Kennedy, on the advice of US Army General Maxwell Taylor, stopped the AR-15 request on the grounds that having two different calibers within different military branches was a bad idea. However, another US government agency sent a batch of the new AR-15 rifles to South Vietnam, where it met with widespread praise by its users.

President Kennedy had appointed Mr. Robert McNamara as the Secretary of Defense at this point. Mr. McNamara was a former Ford Motor Company executive, who had risen up the ranks in Ford, becoming the first non-member of Henry Ford's family to become the president of the company. He had built his reputation by stopping Ford's losses in the late 40s and 50s by bringing in modern organization, management control and planning systems and was a big proponent of efficiency. Mr. McNamara started to push the various branches of the US military to adopt some common weapons, vehicles and aircraft to cut down costs (He was famously known as "Mac the Knife" in the Pentagon, for his cost-cutting measures). Now, after the enthusiastic reports about the AR-15 from South Vietnam, Mr. McNamara had to decide whether to believe the Pentagon's decision on sticking with the M14 or going with the positively glowing reports from South Vietnam about the new AR-15.

So he ordered Secretary of the Army, Cyrus Vance, to conduct tests between the M14, the AR-15 and the AK-47. The test results showed that the Army favored the existing M14, but then subsequent investigation showed that the testing methods were biased by the testers to favor the M14. In the end, Mr. McNamara ordered M14 production to stop in January 1963 because he determined that only the AR-15 could serve the needs of all branches of the US military. This was at a time when 5.56x45 mm. ammunition was not available widely, so the US Army tried to resist the change to the new rifle. The US Army also conducted a series of tests and wanted a few improvements done to the weapon:

• Adding a chrome lining the inside of the barrel and the firing chamber in order to resist corrosion and wear and tear.
• Adding a forward assist lever to push the rifle bolt into battery, in the event that a cartridge could not load into the chamber correctly due to corrosion or dirt.
• Cleaning kits for the rifles.

Colt insisted that the design was self-cleaning and needed no maintenance and in order to cut costs, the first versions of the new rifle were released with no cleaning kits or chrome lining. Colt and the US Air Force also didn't want to add the forward assist lever, because it added an additional $4.50 to the cost of each rifle, but the US Army insisted upon this change. In the end, Colt decided to produce two versions, a US Airforce version called the M16, which has no forward-assist lever and another version, called the XM16E1, with the forward assist lever, for the other military branches. The XM16E1 was renamed as the M16A1 by the US Army. In November 1963, Mr. McNamara approved the US Army's order for 85,000 M16A1s for the US Army and an additional 19,000 M16 models for the US Air Force.

The M16A1 was sent to equip US troops in Vietnam, in 1965. Almost immediately, reports of jamming issues and malfunctions began to emerge. In several cases, dead US troops were found with jammed M16A1 rifles. A Congressional investigation was launched and the key culprit emerged -- it was the propellant used for the cartridges. The original cartridges used during the evaluation tests were manufactured by DuPont and used nitrocellulose based powder. However, these cartridges could not be profitably mass-produced and their propulsive force was just a bit below the desired specifications, when used in arctic conditions. Hence, a new cartridge from Olin Matheson was used instead, which used a mixture of nitrocellulose and nitroglycerin. This new propellant caused dirtier residue than the propellant used in the original cartridges when the rifle was first evaluated. Due to the fact that the rifle came with no chrome lining or cleaning kit, build up of residue could cause jamming issues. The new cartridge also burned faster and therefore increased the rifle's firing rate from 850 to 1000 rounds per minute, which caused extra stress on the rifle's springs.

Once the issues were identified, the US military quickly added chrome lining and also added a buffer system to reduce the firing rate to 650-850 rounds per minute. Cleaning kits and maintenance instructions were also issued and the rifle's failure rate immediately dropped. However, the early reliability issues gave this rifle a bad reputation in the beginning, and this bad reputation continued to dog the M16 for some years afterwards, even after the issues were all fixed. By 1968 though, the rifle began to gain popularity from US soldiers. A 1968 survey among 2100 US soldiers showed that only 38 individuals had wanted to replace the M16 with another weapon and of those 38 people, 35 of them had wanted the CAR-15, a carbine version of the M16!

Other NATO countries also wanted to share commonality with US military firearms and hence, they all began to adopt the 5.56x45 mm. cartridge. 

In the next post, we will study the development and insight into the design of the various M16 variants that followed the M16A1 model.

History and Development of the Assault Rifle - V

In the last few posts, we have been studying the developments of the AK rifle family designed in the Soviet Union. In the next few posts, we will study the development of the M16 assault rifle in the US.

We start our study around 1948, right after the end of World War II. An official US Army historian, Colonel (later Brigadier General) S.L.A ("Slam") Marshall was beginning to study the effects of combat on men and eventually authored several books on the subject. One of the most well known books was titled Men Against Fire, in which he claimed that during World War II, when US soldiers who were engaged in direct combat, 75% of them never fired their weapon directly at an enemy even when they were in combat. Per his research, there appeared to be a deep reluctance to kill another human being even at the risk of being killed. While some of SLA Marshall's research methods and conclusions were questioned much later on, in the 1950s and 1960s, he could do no wrong and was regarded as the ultimate authority. Other studies by the US army showed that people armed with automatic weapons were more likely to fire them in combat, because they were less likely to think about the consequences of killing another human. Still other analysis by the US army determined that most infantry combat occurred at relatively close ranges and that the side with the most firepower tended to win most engagements. The number of casualties of the enemy was found to be directly proportional to the number of bullets fired.

All these studies pointed to the fact that infantry soldiers should be provided with automatic weapons. However, this meant that the soldiers would use up ammunition more rapidly and would need to carry more of it into combat. This meant that the size and weight of the ammunition would have to be reduced in order to avoid overburdening the soldier. A research team in the US Army's Aberdeen Proving Ground facility in Maryland, was tasked with researching the effects of smaller calibers. They found that a .223 caliber (5.56 mm.) bullet moving at higher velocities had the same effects as larger rifle rounds in many combat situations and requested further funding from the US military to perform more experiments.

At the time that the US army was experimenting with smaller calibers, a division of Fairchild Aviation called ArmaLite was formed in 1954, to investigate uses of new materials and new designs for the firearms industry. It was a very small company at that time and the ninth employee was a talented weapon designer and Marine, who had served during World War II, Mr. Eugene Stoner. They produced an innovative rifle for the 7.62x51 mm. NATO cartridge that was in use at that time, called the AR-10. The AR-10 had several new features that were later featured in the M16. It used a direct impingement gas-operated action, unlike other piston and cylinder driven firearms (such as the AK family) used at that time. The direct impingement action didn't have a moving piston and hence was lighter and easier to keep pointed on target, especially when firing in fully automatic mode. Another feature, which was borrowed from the German FG-42 and Johnson LMG was the idea of a straight-line stock (i.e. the rifle stock is in line with the barrel), which serves to reduce muzzle climb. Previously, rifles would have a bend in the stock, so that the sights would be at eye level, while the recoil could be transferred to the shoulder of the user. With the stock inline with the barrel, a lot of the muzzle climb is significantly reduced (read the article on muzzle-climb linked above for why) and therefore, Armalite increased the height of the sights to compensate and the rear sight was mounted as part of the carrying handle.  The receiver was hinged (a feature also found on the FN FAL), but unlike most other rifles, it was constructed of aluminum alloy, which made it lighter than other rifles of its class. The bolt locking mechanism was also innovative for its time. The AR-10 was much lighter, smaller and easier to control in automatic fire than any of its competitors. However, against the wishes of Eugene Stoner, the president of Armalite wanted the barrel to also be made of aluminum/steel composite, which made the rifle's barrel weaker. Hence, when they submitted it for army evaluation, it burst under a torture test and was rejected. Armalite quickly replaced the barrel with an all-steel model, but the damage was done and the US army rejected the rifle. However, the improved model was used by a number of other forces around the world.

Meanwhile, a US general named Willard Wyman received the funding request from the Aberdeen Proving Ground facility and he formed a team to develop .223 caliber (5.56 mm.) firearms for testing. The finalized requirement asked for a firearm capable of selective fire, to be under 6 pounds (2.7 kg.) when loaded with 20 rounds. The bullet had to penetrate a standard US steel helmet of that time period from 500 yards, while exceeding the wounding properties of a .30 carbine. General Wyman had also seen the AR-10 trials and was impressed by some of its innovative features, so he personally asked Armalite to design a weapon using the 5.56 mm. cartridge. The result was a scaled down AR-10 model called the AR-15:

AR-15 assault rifle. Click on image to enlarge. Public domain image.

The AR-15 entered the design competition and the weird thing was that it entered with very little competition, because the main competitor (Springfield Arms) did not feel like diverting resources because they wanted to concentrate on M14 production, which the US military was already using. The only other competitor was an entry from Winchester called the LMR.

During the testing, it was found that rainwater could accumulate in the AR-15's barrel (as well as in the Winchester's barrel), due to the smaller diameter and capillary action. When such a rifle was fired, it could cause the barrel and action to burst. See myth #3 for the reason why. History buffs may also like to read a declassified report of the issue. The rifle was not as accurate in arctic conditions either. However, its lightness and rate of fire meant that an 8 man team could have the same firepower as a 11 man team using the M14 rifle.

In the next post, we will look into the adoption of the AR-15 and how it morphed into the M16

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.

Sights: Zeroing a sight

In the last few posts, we've studied various types of sights. Irrespective of the type of sight used, it must be adjusted so that it points to the spot where the bullet will impact when the trigger is pulled. Such an operation is called "zeroing". We will now study how to zero a weapon.

There are quite a few issues to consider when zeroing a weapon. We will study these first.

The first issue that must be realized is that a bullet fired from a firearm doesn't travel in a straight line. Instead, it travels in an arc and also drifts to one side. We discussed why this happens and also defined two terms called windage and elevation during our study of sight basics. Therefore, if a bullet strikes exactly the point we're aiming through the sights, from a distance of (say) 50 meters, it will definitely not strike the point that we're aiming at, from a distance of 100 meters (assuming the sights aren't adjusted for elevation and windage) because of the way the bullet moves. Hence, when we say that a firearm is zeroed, there must be a reference distance to the target, at which the sights are zeroed. Since different weapons have different shooting ranges, the reference zeroing distance depends on the type of weapon and the ranges it is typically expected to be used. For instance, pistols may be zeroed at 15 meters or 25 meter range, but an M16 rifle is typically zeroed at 200 or 300 meter range. Even though most pistols can be fired beyond 25 meters and the M16 can shoot well beyond 300 meters, the reference zeroing distance is the distance at which it is typically expected to be used under most conditions.

The second issue is to note is that different manufacturers of cartridges may make propellants which produce different amounts of energy and the profiles and weights of the bullets may be slightly different from manufacturer to manufacturer. These could also affect the path of travel of the bullet. Hence, when the firearm is zeroed, it is normally zeroed with the type and brand of ammunition that it is most expected to be used with.

The third issue that affects where the bullet strikes is based on the individual and the angle that he/she holds their head and peers through the sights, when aiming the weapon. For instance, many rifle shooters place their head so that the tip of their nose barely touches the rifle stock. Since different individuals have different shaped heads, therefore a weapon that has been zeroed for one individual will not necessarily strike the same point if another person is aiming the weapon.

The fourth issue is that as there is wear and tear in the firearm, it may shoot differently after some use, due to wear of the rifling, chamber etc. Rough usage may also misalign the sights. Hence, all weapons will need to reset their zero after some use.

With that said, we will discuss a procedure to zero the iron sights of an M16 rifle (or its civilian variant, the AR-15). The same basic principles can be used for zeroing any type of pistol or rifle for any type of sight.

For an M16 or AR-15, the US Army and US Marine Corps advocate the reference distance for zeroing the rifle to be 300 meters. The actual procedure is done at 25 meters though, using a target that has everything scaled by 1/12th actual size.

The M16 has aperture type iron sights, which we studied about previously. Both the front and rear sights are adjusted in discrete incremental amounts. Each time they are adjusted by one increment, a click sound is heard. Hence, adjustments are specified in number of click steps.

Initially, the user adjusts the sights so that the rear sight is using the larger aperture hole (the 0-2 aperture) and turns the windage knob so that the windage indicator is centered about the windage scale, as shown in the image below. The elevation knob in the rear sight is then set to the 8/3 setting (300 meter setting mark. We will discuss why this setting is labelled "8/3" at the end of this article.) and then clicked one click clockwise past it initially. This rear elevation knob will not be touched again until the adjustments are completed.

Next, the front sight post is adjusted. Note that the front sight is mounted on a flat disc with four notches cut on its edge. There is a spring loaded detent that enters one of these notches and locks the sight in place. To lower or raise the front sight post, one must depress the detent with a special tool (or a sharp object, such as a nail or a bullet tip) and then rotate the sight post clockwise or counterclockwise as needed. Each rotation of 90 degrees produces one click. The front sight is raised or lowered until the base of the front sight post is flush with the front sight well.

At this point, the rifle is said to be set at "mechanical zero" initially.

Next, the weapon is taken to the range and placed on a firm base, such as a bench rest. In the case of an M16, there is a special zeroing target sheet that can be placed at 25 meter distance away from the rifle. The target sheet is appropriately scaled to simulate a target at 300 meter range. The zeroing target sheet is shown below:

The target sheet has a black silhouette with a circle in it. This is the part that the user is supposed to shoot at. There are also eight circles around the black silhouette, each one topped with an arc with an arrow head on one side of the arc. These eight circles indicate which sight to adjust (front elevation or rear windage knob) and the arrows indicate the direction to turn the sight adjustment (clockwise or anticlockwise) to adjust the shot towards the center of the target. Notice that there is also a grid in the target sheet and there are numbers that are on the edge of the grid. These numbers tell the user how many clicks to turn the front sight elevation or rear sight windage knobs. The numbers on the X axis are for how many clicks to turn the rear sight windage knob and on the Y axis are for how many clicks to turn the front sight. On an M16, turning the front elevation sight by one click moves the impact point of the bullet up or down by one grid square. Turning the rear windage knob by three clicks moves the impact point of the bullet by one grid square left or right.

The user initially mounts the rifle on a bench rest (or tries to get as stable a shooting position as possible, using a prone shooting position, sandbags for support etc.) and aims for the center of the black silhouette and fires 3 shots. The user then walks up to the target and examines it and sees where the three bullet holes are and determines their average center. The user then looks at the grid and determines which sights to adjust and how many clicks to adjust them by. Let's say the bullets impacted 5 squares to the right and 2 squares down from the center of the target. Then the user knows from the grid markings that he has to adjust the front elevation sight by 2 clicks clockwise and rear windage knob by 15 clicks anticlockwise. Then the user walks back to the bench rest, turns the sight adjustment knobs appropriately and then shoots 3 more times. Then the user walks back and examines the three new holes and sees if they are hitting the center of the silhouette now. If not, the user again looks at the edge of the grid and determines which sights to adjust and by how much and repeats the procedure until the center of the silhouette is hit to the user's satisfaction.

Now the user turns the rear elevation knob in the rear sight one click counterclockwise, back to the 8/3 setting (the 300 meter setting mark. Remember that it was turned one click clockwise past the 8/3 setting initially). At this point, the rifle is fully zeroed at 300 meter range. To shoot at different ranges, the user now merely needs to turn the rear elevation knob to the appropriate range setting.

The following video shows how the procedure is done:

Of course, this procedure simulates the 300 meter range by using a scaled target at 25 meters. Hence, any small deviation at 25 meters may become more prominent at 300 meters. Therefore, some precision shooters adjust their sights as above, but then take their weapon out to an actual 300 meter range and test to make sure it shoots correctly there also and make minute adjustment changes as needed. Then they set the rear elevation knob to different range settings, such as 400 meters, 500 meters etc. and fine tune the settings appropriately. This way, any small errors will be minimized at longer ranges and negligible at shorter ranges.

Incidentally, this might be a good place to explain why the M16 rear elevation control says "8/3" for the 300 meter setting. If you look at that knob, its minimum setting corresponds to the "8/3" mark. The 3 means the setting for shooting at 0-300 meter range. Now, if the knob is turned 3 clicks, the next visible digit is 4, which is for shooting at approx. 400 meter range. Three more clicks brings the next digit 5 for shooting at approx. 500 meter ranges, the next digit is 6 for 600 meters, the next is 7 for 700 meters and then when the knob is turned further, it completes one full rotation and comes back to the "8/3" setting, which is now the setting for the 800 meter mark, the max. elevation setting on the M16A2. This explains why that mark is labelled "8/3". On M4 rifles, the corresponding knob is labelled "6/3" because the max. elevation setting on an M4 is for 600 meter range.

Since accuracy is affected by wear and tear, temperature, vibration and shock, rough usage (i.e. the sights get knocked out of alignment) etc., it is necessary to re-zero the weapon periodically. How often this is done depends on the user, or organization procedures. For example, different branches of military forces have different requirements on how often to zero weapons.