What is the Difference between AR 15 vs M4?

As an Amazon Associate I earn from qualifying purchases.
Our Associate portal can be found here

The difference between the AR 15 and M4 is that the M4 has either a full-auto or burst fire mode whereas the AR-15 does not. There are also other minor differences such as attachments and barrel length, but these do not have any fundamental effect on the rifle. In this article, we will consider the history and differences between the AR15 and the M4. 

There is a lot of talk about the AR-15 and especially M4 both in the news and the firearms community but do you ever wonder what the differences are between them? The most popular modern rifles in production are the AR15 and the M4. If you have an easy eye then these two rifles are virtually identical. There is a lot of confusion as to exactly what differentiates them. 

Because both are available in both automatic and semi-automatic versions. They become even more similar which makes the comparison that much more essential. 

How Were the AR15 and M4 Born?

The fundamental principle that may differentiate each firearm from the other is its origin. Both the AR 15 and M4 rifles came into existence in their unique way. Both also have experienced a long history of development and that is why they perform well today. First and foremost, spend a little time learning about the development history of AR 15 and M4.

History of AR15 

The name derives from the company that first manufactured it. As a result, the AR 15 has become the most popular civil gun. It is also known as ArmandLite Rifle-15, it was created by ArmaLite – then a small company in Hollywood in the late 1950s.

Afterwards, in 1959, ArmandLite sold the AR 15 model for the gun manufacturer Colt Firearms. Following this event, the evolution of the AR 15 model was realized and it significantly improved.

With the significant advancements in function and design, the new version of AR 15 gained immense popularity. The American military adopted it and began production in large quantities. On the other hand, separate manufactures different from the Colt, called Bushmaster, produced variants of the AR 15 as civil guns to the civilians.

To date, other manufacturers besides Bushmaster, have also taken into the manufacturing successful variations of the AR 15 for civilian use. They include DPMS Firearms and Stag Arms among others. 

The latest variations of the AR 15 have two new and interesting upgrades. One is a bump-fire stock that allows you to simulate full-auto fire. The rifle recoils into the stock when you take a shot. It moves the trigger away from your finger, and when it returns, you can hit the trigger again. The action sends another round downrange.

The second variation is new to the market and it is the Binary trigger. You pull the trigger back, it fires- you release-it fires another round. Simple as that. Wondering what caliber the AR15 uses, checkout our article on What is the Caliber for AR15 Rifles?

History of M4

The M4 Carbine is among the best choices for military use. In the firearm community, it is regarded as a considerable improvement over the M16. The M16 is based on the prototype of AR 15. Logically, The M4 took long strides as compared to AR 15.

The concept started in the late 80s, after revelations from numerous wars, the American military realized that the area for fighting was increasingly getting narrowed. At most times, it was only around 200 square meters. For this reason, the best firearm is the ones that are shorter and lighter and this desire led to the birth of the M4.

What are the Differences between AR 15 and the M4?

The same is true. However similar both rifles appear you must be able to tell them apart. From history to structures and functions. But we can still find out some differences between them. 


The first difference is that the Armalite AR 15 is classified as an assault rifle whereas the M4 is a selective-fire carbine.


In terms of length, the M4 is a military rifle and must meet military-related demands. The M4 is a bit shorter than the AR15. If you prefer metrics, the M4 Carbine is 33 inches long while the Armalite AR15 is 39 inches is the length.

Barrel length 

Barrel length makes AR 15 and M4 different from each other. While the barrel of an M4 is 14.5 inches (that is equivalent to 370 mm) in length, the AR 15 has a 20-inch barrel (equivalent to508-mm barrel).

One more point about the M4 barrel is that it is shaped into an hourglass. It is a feature that allows soldiers to put grenade launchers into the cut.

Gas Tube

Because the AR 15 has a longer barrel length than that of the M4, leads to the fact that the AR15 also has a longer gas tube than M4.

Because of this feature, the M4 has had some problems related to the reduced pressure. It is why the M4 feed ramps are adjusted and improved to ensure the proper cycle and operation of the next round.

Velocity and Effective Firing Range

Velocity and effective firing range also highlight the differences between both rifles. Particularly, with 5.66 mm ammunition, Armalite AR 15 features an effective range of 500 yards and has the velocity of up to 3,300 ft. /s.

The number is slightly different compared to that of the M4, whose effective shooting range gains 550 yards and velocity achieves only 2,970 ft.


The M4 receiver is machined with an extra room of specific dimensions to allow the installation of an auto-sear. It is an extra piece of the trigger group that allows automatic fire when you switch the selector to full auto.

In a semi-auto model, both the M4 & AR 15, once a round is fired the action cycle cocks the hammer which resets once you release the trigger. You must pull the trigger a second time to fire another shot.

In full auto, the auto sear acts as a hammer release if you do not release your finger from the trigger. The bolt cycles, and once the next round is fully chambered, the rear part of the bolt carrier will push down on the auto sear which releases the hammer to fire another round. This cycle will continue automatically until you release the trigger, or when you expend all ammo in the magazine.

The civilian AR-15 receiver has no accommodation for an auto sear, and that is why it is only capable of semi-auto fire.

Official Permission

The most notable difference is acquiring permission for using these weapons. The civilian AR 15 is allowed to be used in most states and their purposes include hunting or self-defense.

In contrast, the M4 is only for military use. In other words, if you are a civilian, you rarely get an opportunity to approach this weapon.

There are aftermarket parts filtered into the firearm community and technically lawful for sale, but unlawful when installed. Some parts can turn a semi-automatic firearm into a full automatic firearm mechanically.

It is the argument that surrounds bump stocks. The law becomes thin with regards to a bump stock, as mechanically the AR-15 is still a semi-automatic rifle. Therefore the conditions that make a bump stock illegal are quite sketchy. In the future, gun enthusiasts hope a change in common thoughts as to what can be called illegal and what will remain legal. 

There are lots of gun enthusiasts that may agree that bump stocks are a way to skirt full auto restrictions. In any event, there are dozens of rifles that the manufacturers thought would be adopted by the military. They all have common components and this dilutes the argument that the AR-15 should be banned or restricted comes down to how it looks. 

M4-vs-AR-15 similarities

M4 is a variant of AR15. It should not be a surprise these two guns are quite similar to each other. In the past military-style weapons were identical to keep production costs low. However, rather than installing the rifles with full auto assemblies, they installed them with semi-automatic assemblies.

Place of Origin

The first similarity is that both the M4 rifle and AR 15 are American rifles. It is only a fundamental similarity and has nothing to do with function and use. However, the world considers them such powerful weapons.


Both structures of the AR 15 and the M4 have lots of similarities. Both the interiors and externals show remarkable resemblance. With regards to the internal parts, charging handle, receiver internals, trigger assembly, bolt carrier group, and are similar in both weapons.

As for the externals, rail systems and hand guards come with some similar points.

Most Popular Rifle Accessories

[amalinkspro_table id=”2682″ aff-id=”” new-window=”on” nofollow=”on” addtocart=”off” /]

In Conclusion

Both the AR 15 and M4 are great products from firearms technology. The primary differences are limited to the barrel, gas tube, feed ramps, and fully automatic functioning. In terms of similarities, the two are almost identical.

If you have an AR-15, rest assured that it is extremely similar to the military M4. In the end, the debate between the AR 15 and the M4 is a simple argument. If you consider the evolution of the two rifles it is evident that the M4 is more evolved than the AR 15. It is smaller, lighter, and just as effective.

Amazon and the Amazon logo are trademarks of Amazon.com, Inc, or its affiliates.

Scroll to Top