AR15 vs M16: What’s The Difference?

hen talking about the AR15 vs M16, it is not uncommon to get the two confused. After all, they both look alike, fire the same round, and have evolved over the years with similar technologies.

When talking about the AR15 vs M16, it is not uncommon to get the two confused. After all, they both look alike, fire the same round, and have evolved over the years with similar technologies. But upon closer inspection, there are some very striking and glaring differences between the two. Most of these differences have been caused because of the missions these rifles were designed to carry out.

After all, the M-16 was made at the height of the Cold War to give US troops a deadly accurate, lightweight, and reliable rifle that could beat anything the Soviets could manufacture. On the other hand, the AR-15 was designed with customizability in mind to produce the most accurate and fine-tuned civilian sharpshooting rifle on the market. 

But how are these two related and where exactly do their paths converge? To answer that question, one must go back to the end of World War Two. 


History of M-16

At the end of World War Two, each branch of the military conducted numerous studies on how their service had performed during the war and where they could make technological and tactical improvements. One of those studies was conducted by the Army in assessing the effectiveness of their primary rifle, the M-1 Garand. 

The findings of the report were shocking. On average, it was found that almost 80% of troops who had experienced combat had never fired their weapon. The study ultimately concluded that the reason why the average infantryman rarely, if ever, actually fired his weapon in combat was his individual belief that his efforts of firing a single shot at a time would not affect the outcome of the battle and felt outclassed by larger weapons or an unseen enemy. 

An interesting finding of the study was that those who carried the Browning Automatic Rifle, or BAR, actually beat the statistic and these men fired more often than their rifle carrying counterparts. The conclusion was that these men had greater confidence in their ability to effect change in the course of the battle and therefore fired more often. They also found that soldiers who were near these men also fired their rifles more. 


Therefore, Army officers concluded that soldiers in the future needed to be equipped with a lightweight yet accurate rifle capable of fully automatic fire. The first result of this was the M-14. It was a very large rifle weighing in at almost ten pounds fully loaded with a 20 round magazine of .308 ammunition. It was capable of fully automatic fire and was the standard infantry rifle from the 1950s through the first few years of the Vietnam war. But soldiers in the field had many issues with it. 

AR15 vs M16

Development of AR Rifles as an Alternative to M16

The rifle was unyielding and very heavy. The heavy-caliber also limited the amount of ammunition that could be carried. It was also uncontrollable in full automatic. The Army needed something to replace it and began looking at other options even before the Vietnam War started. One of the earliest contenders to do so was an experimental rifle produced by the ArmaLite company called the AR-10. 

The AR-10 was a revolutionary rifle and was the brainchild of Eugene Stoner. Stoner sought to develop a lightweight, accurate rifle that was reliable in all conditions and could outperform all current rifles on the battlefield. To do so, he developed several unique features that would later become ubiquitous with the M-16, such as its patented gas blowback system, polymer design, and ergonomic build.


To market it to the military, he first chambered it in the standard 7.62×51 mm NATO round. He did so because the military wanted to have their rifles and machine guns, which was the M-60 machine gun at the time, chambered in the same round to reduce logistics issues. 

Initial testing with the AR-10 was quite impressive to the military, but at the time of these tests in the late 1950s, the government had already signed a huge contract for hundreds of thousands of M-14 rifles. Undeterred, Stoner went back to the drawing board to come up with a new design to ensure that his rifle would be the one adopted by the military. 

From AR-10 to The AR-15

That new design was the AR-15. The AR-15 was even better than his previous model and incorporated several major improvements. To further decrease the weight, Stoner made the rifles from lighter polymers and plastics in addition to using mostly aluminum parts wherever possible. This reduced the weight by almost a third compared to the M-14. 


Another major improvement was changing the caliber. For the past several decades the military had been experimenting with smaller caliber bullets that could still deliver the power of “full size” rounds like the .308 and 30-06 (pronounced thirty ought six) commonly used in machine guns. The AR-15 model was the first to ditch the desire for a “full-sized” cartridge in favor of a more compact and lighter, yet powerful round called the .223 Remington. 

The benefits of using a smaller round took into consideration the years of study of wound ballistics where heavier, higher velocity rounds simply passed through targets but smaller, medium-sized rounds tumbled and caused wound cavitation- the expansion of pressure inside a target- which caused more damage. 

Medium-sized rounds like the .223 also enabled troops to carry more ammunition than before and created less recoil, meaning more accurate shots and more controllable fully automatic fire.


Stoner was eager to get his creation in front of the military and went to some unordinary measures to do so. At a Fourth of July celebration in 1960, he approached a high ranking general in the Air Force and gave him an impromptu test demonstration. Stoner set up a range of watermelon targets at 50, 100, and 150 yards and asked the general to shoot them. The general was so impressed by the rifle that he requested 100,000 on the spot. This ambitious order was later revised to 8,500 a year later, but Stoner had just won a huge step forward in marketing his rifle to the military. 

Rigorous testing by the US Air Force and Army followed Stoner’s demonstrations for top military brass. All tests proved highly satisfactory and listed the rifle as highly reliable and accurate. The Air Force was the first service to widely adopt the rifle in the early 1960s and once Vietnam started to heat the Army was soon to follow. Within a few years, it was the main battle rifle of the US military in Vietnam through today until its gradual replacement by the M4 Carbine. 

assault rifle

M16 vs AR15: How They Compare

Wondering which is better between AR15 vs M16? Fundamentally, the M-16 and AR-15 are built and function the same. The major components of both rifles are a lower and upper receiver, a barrel, front and rear sights, a magazine well, a charging handle, a bolt assembly, a buttstock, a trigger assembly, and a compensator.


The upper receiver carries the barrel and bolt assembly while the lower receiver houses the trigger, firing mechanism, and magazine well. These are connected to the rifle by Stoner’s iconic push pins first adopted in the 1960s. 

How the rifle works is when a magazine is inserted into the magazine well, the first round is put into the path of the bolt. When the charging handle is cocked back, the bolt carrier assembly is now under pressure and pushes the first round into the chamber when it is let go. 

As the round is seated inside the chamber, the bolt assembly rotates and locks the bolt into place. Doing so prevents the unintended loss of gas pressures when the bullet is fired. 


The round itself is fired when the trigger, which is attached to lugs that prevent the hammer from going forward, is pulled. The hammer then strikes the firing pin, which in turn hits the primer on the round. The primer causes a small explosion that ignites the powder inside the cartridge sending the bullet down the barrel. 

After the round is fired, a small amount of gas enters what is called the gas tube at the end of the barrel. The hot, pressurized gases are then forced onto the bolt assembly. When the pressure is great enough, which happens in fractions of a second, the whole bolt assembly is forced rearward and a reverse process ensues. 

As the bolt carrier travels backward, it unlocks and rotates what is called the extractor. The extractor is the portion of the bolt carrier that pushes the spent casing out of the chamber. The excess gases that were once pushing on the bolt carrier now push on the spent casing as well and force it out of the extraction port. 


When the bolt carrier travels backward, it also cocks the hammer again. Basic physics tells us that every action has an equal and opposite reaction, so when the gases stop pushing the bolt assembly slides forward. Doing so pushes another round in the chamber and the rifle is ready to fire once again.

 AR15 vs M16 Variations

Since the design of the original M-16, there have been several variations to come out that have improved on the initial model, whether for ironing out design flaws or adapting to the needs of the US military. The very first M-16- the one most similar to the AR-15 it was derived from- was the M-16A1. This model is the classic one that people recognize from all the shows and films about the Vietnam War. 

The next version to arise in the 1980s was the M-16A2. This model came about when the military wanted to shift away from the “spray and pray” mentality of fully automatic fire and instead focus on marksmanship. Hence the major change with the M-16A2 was making it only semi-automatic or burst fire capable. 


The M-16A3 came out during the 1990s and briefly went back to the fully automatic mode of fire of its predecessor. However, as modern battlefields changed once more from the Cold War-style confrontations of massed armies in small areas, to fighting smaller scale engagements over large distances, the services adopted their final change to the M-16, the M-16A4.

The M-16A4 reverted back to the M-16A2 design of being capable of only semi-automatic and three-round burst fire capability. Another major change was the addition of a rail system on both the barrel and upper receiver. By adding this rail system, the new design enabled advanced optical sights, lasers, and flashlights to be added or exchanged with ease, thereby increasing the capability of the average rifleman greater than ever before. 

As far as raw data, the AR-15 and M-16A4 are close contenders. The M-16A4 and AR-15 both weigh in at about seven pounds fully loaded. The M-16A4 has an average effective range of 550 meters while the AR-15 lags, with most firearms experts agreeing that the effective range for civilian shooters are between 400-600 meters. Both rifles are also manufactured standard with the .223 Remington round.


 What are ar15 vs m16 core design features

While the AR-15 and M-16A4 are both based on the same core design, there are a variety of features, both functional and cosmetic, that would make one better than the other.

One of the main differences in AR15 vs M16 is the closed third hole in the sear. The sear is the portion of the rifle that determines what mode of fire it can shoot in. Most AR-15s have this third hole on the lower receiver that was a leftover from the M-16A1 design which enabled fully automatic fire. Civilians could in theory drill a hole through it and make a few other modifications to make it fire full auto, but doing so is a felony and highly illegal. 

The M-16A4 by default has more firing options than civilian owned AR-15s. 


Another critical design difference between the AR15 vs M16 is what is called the forward assist. The forward assist is a button attached to a handle on the right side of the M-16A4 that enables the shooter to manually push the bolt all the way forward to seat the round fully in the chamber. The feature was added by Stoner during the Vietnam War when reports from the field came back that the rifles would jam incessantly. 

While the root of the problem uncovered in a subsequent Congressional investigation found that the cause of the jamming was the military using an improper propellant in their ammunition that Stoner had warned them not to do, the forward assist has nonetheless remained an integral feature of all further M-16 models. That is because soldiers operate in some of the harshest environments in the world and while they may clean their rifles frequently, dirt and debris are always quick to find a home inside rifles, which makes the addition of a forward assist crucial to ensuring reliability. 

AR-15s on the other hand do not come standard with a forward assist. While some certainly do, there are no “standard” models of AR-15s like there are M-16A4s for the military. Civilian and police shooters face a more arduous task of clearing jams and malfunctions than their military counterparts. 


m16 vs ar15 customizability

The AR-15 does have the advantage of customizability, especially with the mixing and matching of uppers and lowers. One of the benefits of this is allowing shooters to modify the caliber of their rifle from the standard .223 up to a .50 caliber BMG or even down to pistol cartridges like the .22 or 9mm. While having the ability to change out calibers using different receivers does provide a lot of versatility, it is not something that could be done in a firefight and is somewhat cost-prohibitive both for the receiver and the often rare ammunition that is shot through them.  

AR-15s also have the advantage of a wide range of magazines that can be used in the rifle, including 100 round drum magazines, since the M-16A4 is only issued with the standard 30 round magazines the military has used for years.

Between ar15 vs m16 which more durable? M-16s do beat out AR-15s is another feature and that is the addition of the chrome-lined barrel. During the Vietnam War, it was discovered that by plating the inside of the barrel with chrome, the life expectancy of the barrel could be increased and the amount of corrosion decreased. While the effect of chrome-lined barrels on accuracy is still a hotly debated topic, the fact that they increase reliability is a proven concept. AR-15s have the option of chrome-lined barrels but this feature is an additional cost for the buyer and does not come standard in all AR-15s. 


The last few differences between the ar15 vs m16 are merely cosmetic and demonstrate the military utility of the M-16A4 over the AR-15. The M-16A4 comes standard with a carrying handle while most AR-15s do not in favor of extra space for rails to put scopes, sights, and other gadgets. AR-15s usually do not come with a bayonet lug either and some do not have sling studs to mount a sling which would make carrying long distances cumbersome and tiring. 

In order to determine which one is better between ar15 vs m16 , it would really depend on what the rifles were needed for. If the user needed a rifle to arm a large group of people for combat, the M-16A4 would be the choice due to its increased reliability and standard configuration that makes manufacturing, training, and employing large quantities of rifles both efficient and at a lower cost. 


If the user wanted the ability to customize and get the most out of the AR/M-16 platform, the AR-15 would undoubtedly be the winner due to the wide range of calibers, gadgets, barrels, and magazines that can be interchanged to produce the most effective rifle possible. However, the capacity to equip large armies with this kind of setup is not likely due to the small limited market of these calibers and high cost. 


As for saying which one is better between ar15 vs m16 , it is best to say that the M-16A4 would outclass most AR-15s in a battlefield environment but that the M-16A4 could be outclassed in the civilian world say in a marksmanship competition due to the amount of customization that can be done to it. See more