What Is The Difference Between An AR-15 vs. M4?

Shooting is an enthralling activity, and shooting using big guns is even more exciting. The AR-15 and the M4 Carbine are both modern rifles. They are two of the most widely seen guns in the world today and are very proficient at causing damage whenever needed. Here, we will try to distinguish between the nuances of the two guns. We will try to dismantle the subtle differences in structure and function between both firearms.  

The M4 is that the AR-15 is a civilian weapon, whereas the M4 Carbine is strictly used by the military. Both rifles are very similar in nature. For starters, they look like twins separated at birth. We will find out more about both guns as we dive deeper into this story. 

Origins of the rifles 

Gunpowder was an important invention in the world. It gave the world firecrackers and the Second World War. Consequently, some of the most significant innovations in firearms technology took place in the years after WW2. In WW2 combats, soldiers had to carry heavy weaponry over long distances. Gunmakers tried to solve that problem by creating lightweight guns. However, these guns were not powerful enough to deliver bullets over long distances. Hence, militaries across the world decided to generate the production of rifles. Rifles became longer firearms that could hit targets further away with more power.  

Do you know what the “M” in M4 stands for? The answer is surprising because it is very mundane. The “M” stands for “Model.” So, when we talk about an M4 Carbine, we are shedding light on the fourth model of the Carbine gun. Every new gun will have its own series of models. Each category of firearms is considered for a new line of nomenclature. Funnily enough, while the M1 rifle was a WW2 legend, the M2 was a training rifle that fired small cartridges. In the series of famous M-weapons, only the M1 and the M14 have been true combat firearms.

 Soldiers in WW2 found it extremely challenging to shoot enemies over 300-400 yards. To solve that problem, gun manufacturers decided to develop the abilities of rifles. Gradually, the M1, M2, M3, and M4 Carbines grew in popularity. These big guns led to the development of newer rifles like the M16 and the AR-15. Makers of the AR-15 initially intended for the weapon to be used in combat. However, that was not the fate of the AR-15 rifle. 

History of the AR-15  

We go back to the decade after the end of the Second World War. In 1956, a company called ArmaLite in the USA aimed to set a new benchmark for rifles. The company wanted to solve all problems that existed with all standard rifles and create a menacing machine that would be the apple of the army’s eye. They also tried their hand at making an ideal bullet cartridge that would suit their new rifle.  

So, in 1956, the ArmaLite AR-15 set out into competitive trials against the M14, which was then known as the T44. Back then, the ArmaLite rifle was called the AR-10. Testing did not go well for the company. Parts of the barrel were damaged in the arduous tests, and the AR-10 fell in the eyes of the military. Thankfully, the company did not stop its efforts. They were relentless in remodeling the gun. The new model was the coveted AR-15 rifle.  

The company made one crucial change to the AR-10. They made it smaller when they manufactured AR-15s. ArmaLite tried to enter the gun race soon. However, testing and development were a rigorous process. In 1959, the company ended up selling the property for the AR-15 rifle to Colt. Colt, being one of the biggest gunmakers in the world, launched the 601 rifles. The 601 was the first Colt product based on the AR-15 design. Very soon, Colt 601 was adopted by the military. After the turn of the decade, in 1962, the US Army adopted the gun into official use and called it the M16 rifle. So, to conclude, the M16 rifle that was one of the most long-standing popular choices of the US military is actually the latest version of the original AR-15 gun. 

History of the M4 Carbine rifle 

It is no coincidence that the history of guns begins with war. Whenever war has been inadequate, we have looked to design better guns. In the same fashion, when the Vietnam war was growing cold, the US military aimed to develop an offspring of the then famous M16 rifle. Back then, most military units were happy using several varieties of the M16 rifle, like M16A1, M16A1E1, etc. However, the army found that it was not the best choice for close combat in testing the gun. Close combat demanded a slightly smaller yet equally powerful gun – a Carbine variant.  

To begin such close-quarter operations, the CAR-15 family of weapons came into existence. It continued to be a part of the Vietnam war. The CAR-15 was created by decreasing the barrel length in half to approximately 10 inches. While that mod was giving additional muzzle energy to the bullet, the army was compromising on accuracy and range. Till future iterations of the gun could be designed, the CAR-15 was categorized as an SMG – a submachine gun. It had a slow caliber and short range. The weapon was also named the XM177 Commando. 

What happened next is astounding since it is the defining turn in the story of the M4 Carbine. In 1982, the US government approached Colt and asked them to make a carbine gun based on the M16A2. Colt was selling the M16A2 rifle as the ‘Colt 645.’ For the carbine variant, Colt modified the XM177 Commando with the help of the munitions arm of the government. The resulting phenomenon was called the XM177E2. It was later dubbed the XM4 Carbine rifle. The primary distinction between the XM4 Carbine and the M16A1 was that the XM4 fired the M855 cartridge instead of the Remington .223 bullet. 

The army then began looking for a gun to replace the M3 SMG. Therefore, they were looking for a weapon that fired 5.56mm cartridges instead of the usual 7.62s. In 1986, several groups in collaboration finished developing the gun we now identify as the M4 Carbine. The army bought only 892 guns in the first year of service in 1987. However, by the time the Gulf war broke out in 1993-94, the demand for the M4 shot up. 

Difference between AR-15 and M4 

There are considerable differences between the two rifles, even though they have very similar origins. It is also not very difficult to tell them apart because of particular distinctions between their physical attributes. So, let us take a look at some of the key differences between the AR-15 and the M4. 


Classification refers to the bracket of ‘type of gun’ in which a firearm falls. There are quite a few categories, and the classification is determined by the government, gun lobbies, etc. In this case, both firearms fall into different categories. They might both resemble the basic structure of a rifle, but there is still a clear distinction.  

The original Armalite AR-15 has been categorized as an “assault rifle.” An assault rifle has a clear industrial definition. It refers to guns generally used by the military (they are the only ones who should be doing assaults) and guns that have select-fire capabilities. That refers to firearms that can switch between a semi-automatic and automatic mode. Assault rifles are also intermediates between a submachine gun and a rifle. 

 On the other hand, the M4 falls under the title of a “selective fire carbine.” We agree the line is very thin between these two guns. However, the M4 Carbine is closer to the category of submachine guns, whereas the AR-15 is closer to being a rifle. 

Gun length 

The two guns in question might be similar. But you can set them apart at first sight quickly. That is because they are different in size. In fact, the M4 was designed to be a smaller gun than the classic AR-15/M16 design. As a result, you will find that the original ArmaLite AR-15 measures 39 inches in length. However, the M4 Carbine measures 33 inches only. We must understand that the M4 is a military weapon, and it must meet their needs, guidelines, and specifications.  

A significant difference is found in the barrel lengths of the two guns. The AR-15 features a 20-inch barrel, whereas the M4 Carbine has a 14.5-inch barrel. Additionally, the barrel of an M4 Carbine is shaped to equip secondary weapons onto the gun. Soldiers can add grenade launchers to their barrels using the unique shape. 

Presence of Gas Tube 

The structure and size of a gun are instrumental in shaping its internal combustion mechanism. An essential component of a weapon is its gas tube. Since firing a bullet is a combustion process, a gun needs a gas tube to release all the gas generated in it. Among the two firearms that we are talking about, the AR-15 has a longer snout, a longer barrel. That means it also has a more extended gas tube than that of an M4 Carbine. A longer gas tube ensures more suppression, less recoil, and jamming.  

Since the M4 Carbine has a smaller gas tube in comparison, it faces some problems of reduced gas pressure. To combat these issues, the manufacturers have adjusted the mechanism of the gun. It has a modified ramp inside that allows you to move ahead to the next round smoothly. Both guns fire smoothly, no doubt. The M4 Carbine has additional measures to execute the hassle-free firing of every round. 

Ballistics: velocity and range 

The firing range of a gun is also determined by its structure. The muzzle velocity of a bullet also relies on the gun’s build. Both guns, in comparison here, are close competitors when it comes to speed and range. They both make use of the 5.56 x 45 mm bullet cartridges. In that scenario, the range of the AR-15 rifle is 500 yards, and the M4 Carbine’s range is 550 yards. You will observe that there isn’t a significant difference in those numbers. Secondly, let’s talk about velocity. The muzzle velocity of a bullet from an AR-15 is 3,300 fps. The M4 Carbine can produce a muzzle velocity of 2,970 fps for the same bullet. 

 These changes, which seem minute, affect the function of each gun. Because of its lesser velocity, an M4 is used in close combat situations for rapid firing. The AR-15 may be used for mid-range or long-range combat as well. As clear as day, the structure of a gun influences its function. 

Automatic action 

We have stumbled across a facet where the M4 Carbine is a clear winner. The manufacturers of the M4 have designed it in an intricate manner. There are multiple trigger circuits along with the option of automatic action in the M4, which are absent in the AR-15. The M4 Carbine invites the shooter to switch to the automatic fire mode, where you can dispense rapid bursts of fire with a single press of the trigger.  

In the semi-automatic fire mode, both the AR-15 and the M4 fire a single bullet at the press of a trigger. Then the gun resets a shot in the barrel and cocks the hammer. You have to pull the trigger a second time to fire again.  

The M4 is a military weapon and therefore has the option of an automatic action mode. The automatic mode in the M4 acts as a hammer release. It ensures the firing of multiple bullets until you release the trigger. Since the AR-15 is a humble civilian firearm, it can only fire one round when you press the trigger. It does not have an automatic mode. 


The difference here is noteworthy when it comes to these two guns. Since the M4 Carbine is strictly a military weapon, it has the automatic fire or rapid burst option. That service has its place on the weapon for close-range encounters. A civilian would have to work very hard to get their hands on an M4 Carbine. The legal aspect of using an M4 is very tricky.  

On the other hand, the AR-15 is a civilian gun. It is legal for sale and is only used for hunting and self-defense purposes. The legalities surrounding the purchase of an AR-15 are therefore lax. Since getting your hands on an American gun permit is relatively easy, you can purchase an AR-15 anytime, anywhere.  

The real question is – can you convert a semi-automatic gun into an automatic one? The answer is – yes. If you purchase the right aftermarket spare parts, you can build an automatic fire mechanism into a semi-automatic weapon. While the sale of such spare parts is legal, using them to create rapid burst weapons is not. So the laws are shaky in that case. But ultimately, an M4 Carbine is not operated by civilians, and the military does not use an AR-15. 

Similarities between an AR-15 and an M4 

The M4 and AR-15 have risen from the same ground for roughly the same reasons. Therefore, they have some striking similarities. 


Both guns in question are American. While that does not mean they are the same gun, their cradle is the same. Both guns have the “American” image stamped onto them, which gives them an inherent powerful position in the global context.  


The structures of both guns show tons of similarities. Their trigger assembly, receiver internals, bolt carrier group, etc., are all similar in structure. They are built with similar designs, excluding the automatic fire mode in the M4 Carbine. 

M4 vs. AR-15: Which one is the better choice?  

It is very challenging to assess which weapon is better when it comes to these two proficient firearms. Both guns have seen tremendous development in their design because they have been around for decades. However, it is essential to understand that they have been used for vastly different functions in recent years. We agree that the AR-15 was built for military contracts. However, it has become a rifle for homeowners today. Gun enthusiasts, who want to participate in shooting competitions or hunting games, often prefer the AR-15 today.  

On the contrary, the M4 Carbine has largely stayed away from civilian hands. Its primary purpose has been warfare. The gun has also performed its dues whenever necessary. The US spearheaded the war on terror, which has been a success because of the M4 Carbine and its firearm brethren.  

Both guns have stood the test of time and have become preferred choices in their niche. Since both weapons use the same ammo, we have to weigh their attributes against each other. In that sphere, the M4 Carbine trumps the AR-15 because of its automatic fire mode. That alone is a stamp of success on both weapons. 


We have discussed the attributes of two impeccable weapons in this article. They are both very effective and efficient in their spheres and have satisfied users for decades now.

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