What Is the Difference Between an AR15 and an M4?

What Is the Difference Between an AR15 and an M4?


Mathew R Reed
January 27, 2022

If you plan to buy a rifle for hunting or self-defense, you have likely heard of the AR15 and the M4. These rifles come highly recommended in the firearms and military communities in the US.

The AR15 and M4 are alike in appearance, so it can be confusing for first-time rifle buyers to differentiate between them.

In this article, we give you all the details about the similarities and differences between AR15 and M4 rifles so that you can decide which one is better for you.

Let’s dive in.

Why Is There So Much Confusion About the AR15 and the M4?

Why Is There So Much Confusion About the AR15 and the M4?

It’s easy to get confused between the AR15 and the M4 as they have many similarities in design and structure.

This can be attributed to the fact that both rifle designs are based on the ArmaLite Rifle developed by American firearms designer Eugene Stoner in the late 1950s.

For starters, these American rifles have the same bolt and bolt carrier group, along with their charging handle, trigger, and trigger assembly.

The internal components of the upper and lower receivers are nearly identical.

Externally, depending on the AR15 rifle’s configuration, the rail systems and handguards of both firearms can be identical as well.

You can easily swap the parts of the AR15 and the M4 due to their similarities in construction.

What Is the Difference Between an AR15 and an M4?

What Is the Difference Between an AR15 and an M4?

There are very few differences between the AR15 and the M4.

Some people say that the M4 is the military version of the civilian AR15. This is not entirely true. The M4 is actually the carbine version of the M16, which, in turn, is the military version of the AR15 rifle.

The M4 is a carbine-length rifle used for military purposes, which is why it has a shorter barrel length of 14.5 inches. The standard version of the AR15 has a barrel length of 16 inches.

But note that longer barrel lengths can also be found for the AR15 as it has several different versions.

However, the US law on short-barreled rifles requires a minimum 16-inch barrel length for civilian use.

The M4 also has a smaller gas tube than the AR15 in proportion to its barrel. This causes a decrease in pressure.

But the M4 compensates for this shortcoming with modified feed ramps to enable the next round to be properly seated.

As the M4 is used by the military, its barrel has a cut-out in the shape of an hourglass, where a grenade launcher can be mounted. The AR15 doesn’t have this feature.

The M4 also comes with a collapsible, six-position stock configuration. In contrast, the standard AR15 features a fixed stock.

But due to the many different variations of the AR15, you can also find collapsible stock configurations for it.

The AR15 is also more lightweight and faster than the M4. The AR15 has a velocity of up to 3,300 feet per second, whereas the M4 only reaches up to 2,970 feet per second.

In terms of the firing range of each rifle, the M4 performs better as it can reach 550 yards, while the AR15’s firing range is only 500 yards.

The fundamental difference between AR15 and M4 rifles is their selective-fire features.

The AR15 has a semi-automatic firing mode, which means that it loads the rounds into the chamber automatically but needs manual pulling of the trigger for discharge.

Meanwhile, the M4 can fire either in a 3 round burst, a semi-automatic, or fully automatic mode.

Lastly, the lower receiver of the AR15 does not have an auto sear and third trigger pinhole like the M4, as the former is not a fully automatic or assault rifle.

Which AR15 Is Most Like an M4?

Which AR15 Is Most Like an M4?

The AR10 is a derivative of the AR15 and is touted to be identical to the M4A1 in its functionality and ergonomics. However, it cannot fire fully automatic.

The military select-fire version of the AR10 has a fully automatic firing mode, making it even closer to the M4.

Why Is M4 Illegal?

Why Is M4 Illegal?

Civilians cannot buy or own a select-fire or fully automatic M4 carbine as it is classified as a machine gun developed after the 1986 US ban.

Hence, it is restricted to the military and air force and cannot be owned by private citizens.

If you want to get an M4 rifle for personal use, you can buy one with a lower mil-spec and identical handguards.

Civilian versions of the M4 have 16-inch barrels and can be fired only in a semi-automatic mode to meet the requirements of the Gun Control Act.

Technically, civilians are allowed to own the initial prototypes of the M4 sold by Colt before 1986.

However, they are so limited in quantity that they are priced incredibly high. They are only sought after by gun enthusiasts who really wish to own a real M4.

Is 3 Round Burst Legal?

At the federal level and in most states in the US, a 3-round burst is legal. Under the National Firearms Act (NFA), it is classified as a machine gun, and machine guns are legal in most states.

However, each state has its own laws about the legality of the 3 round burst, and a few states have banned it.

It’s important to note that even in states where a 3 round burst is legal, you need to register the gun as a fully automatic firearm.


Which one is better, the AR15 or the M4?

Although the M4 is undoubtedly better than the AR15 in functionality, it can only be used by military personnel. Civilians can only own an AR15 for personal use.

This shouldn’t pose too much of a problem, as the AR15 is almost entirely identical to the M4 and only lacks the fully automatic firing mode.

The AR15 is also highly customizable and readily available, making it popular in the firearms community.

If you are a civilian who wants to own an M4, you can buy a lower mil-spec with M4 handguards. You can also legally buy an AR15 with an M4 barrel length if you want the M4 look.

For this, you need to pass an NFA background check and buy a $200 tax stamp.

It is also possible to own a fully automatic AR15 produced before 1986, but they are rare and very expensive.

What are your thoughts on the differences between AR15 and M4 rifles? Do you have a preference?

Are you an enthusiast who wants to own an M4? Let us know in the comments section below.


Mathew R Reed

Mathew R Reed is a professional gun seller who runs a dedicated gun store in the suburbs of Oakland, CA. A hardcore hunting enthusiast since childhood, Reed has ample experience with guns and accessories. He is the founder of ArmorHoldings.com and creates some of the most helpful gun-buying guides and explainers. If not in the gun shop, you can find him on the nearest hiking trail or nearby hunting spot.