M4 vs AR-15 – Read This First

M4 vs. AR-15
Alfred Mendoza

M4 and AR-15 are the two most popular rifles on the market and the firearm community. Since the two guns are almost similar, comparing their differences will help avoid confusion, especially for beginners.

To give you a clearer view, our team prepared a detailed comparison for M4 vs AR-15, including their background, capacity, and other features.

M4 is a fully automatic firearm that uses shorter handguards with shorter barrel length, while an AR-15 is semi-auto and uses longer handguards with longer barrels. 

The AR-15 and M4 receivers may look the same, but M4 has improved feed ramps. AR-15s have longer rifle buffer tubes with stock, while M4 has a carbine buffer with six-position stock making it more modern than AR-15.

How Do They Compare







Origins of the Rifles

History of AR-15

Armalite Rifle 15 is designed by Eugene Stoner. It is not considered an Assault Rifle 15. It was first developed as a military rifle in the late 1950s by the small company ArmaLite [1]. It is to replace the M1 rifle from World War II. But due to financial issues, this model was sold to Colt. AR significantly improved it, and then the rest is history. 

After some development process on the design, the new version has become popular in the American Military. The variety of calibers and multiple lengths has become the favorite of the special forces in the Vietnam War. The US Armed Forces then adopted it as an M16 rifle. It replaced the Thompson Submachine Gun and M3 Grease Gun.


History of M4

The M4 or M4 carbine was made following the improvement of M16 without forward assist. In the late 80s, the American Military needed a shorter and lighter weapon, and the M4 was developed. It is in high demand with the US Military and Special Operations troops replacing the M16 as the primary infantry gun. 

A short barrel, detachable carrying handle, and removable stock allow the soldiers to operate in close quarters. It has improved magazine feed, and the original barrel was 10 inches. It can fire a three-round burst and is known to be semi-automatic. In 1988, Colt began producing the new M4 carbine, which features both AR-15 and Colt Commando benefits.


Closer Look at the Differences


Armalite Rifle 15 is a lightweight semi-automatic version of the M4. Semi-automatic rifles automatically load the rounds into the chamber and prepare for firing, but manually pulling the trigger to discharge is needed. 

On the other hand, M4 is identified as a select-fire carbine. M4 can adjust the firing mode from semi-automatic fire, burst mode, and fully automatic. 

Also Read: Difference Between AK-47 & AR-15

Velocity and Effective Firing Range

Another significant difference between the two weapons is that the AR-15 is faster vs. M4 (XM177 Air Force version). The AR’s velocity can reach up to 3,300 ft/s while the other rifle reaches 2,970 ft/s. The AR bullet travels three times faster than a normal handgun. 

When it comes to the firing range, M4 is greater than the AR. The effective firing range of the M4 is 550 yards, while AR-15s can reach 500 yards only.

Official Permission

The official permission has notable differences between AR-15 vs. M4. Civilian shooters are allowed to use and own AR-15s but with certain restrictions on the barrel lengths. It is allowed for personal use, such as self-defense or hunting.  

On the other hand, the M4 is for the military and air force which means civilians cannot own this gun. However, you can buy a mil-spec lower and the same handguards to have the same weapon.

Official Permission

Stock Configuration

AR-15 is one of the most customizable rifles you can get. It has various options, from accessories to major parts that you can think of. You can also do your stock configuration, allowing your rifle to be both fashionable and functional. M4 can also be modified to some extent. 

Gas Tube

M4 has a shorter gas tube than AR-15s. The barrel’s length is in proportion to the tube. Since the Armalite Rifle 15 is longer, the gas tube is also longer, making it easier to solve the recoil. On the other hand, the pressure may be an issue since the tube is shorter, so the M4 has an adjusted feed ramp to ensure the rifle’s reliability.


AR-15s have a longer barrel than M4. The legal length of barrels in AR-15s is 16 inches based on the ATF. Any barrel lower than 16 inches should secure many documents like an SBR tax stamp to make it legal. 

On the contrary, since M4 is for the air force and military use, a short barrel like 14.5 inches is allowed for them to use. It also comes with an under-barrel grenade launcher.



The receivers on the two rifles are closely the same, but M4 has adjusted feed ramps and auto sear. Recent M4s do have flat-top receivers. Unlike the M4, AR-15’s lower receiver does not have an auto sear and third trigger pinhole. It is because the AR-15 is not an automatic or assault rifle. 

Buffer Tube

There’s a difference between the two when it comes to buffer tubes. AR-15s have long and fixed stock buffer tubes. Since M4 has a collapsible stock, it has a carbine buffer with six-position stock. The buffer tube allows the user to attach a stock to the rifle, enclosing the buffer and spring. The bolt carrier will eject the spent rounds then load the next one. 

Also Read:

AR-15 vs M4 - Are There Similarities?

Since M4 is a product from AR-15, the similarities are undeniable. The internal parts of the upper and lower receivers are similar. The bolt and bolt carrier group has similarities as well as the trigger and trigger assembly. In addition to this, the charging handle, handguards, and rail systems are also the same.  

In most cases, you can interchange the parts of both rifles. The structure of both guns is almost identical, so it shows a remarkable resemblance. The two weapons originated in America, where powerful rifles are produced.


Yes, you can put an AR-15 upper on an M4 lower.  The AR upper will fit on the M4 lower. The inner parts of AR-15s and M4 are almost similar, so you can put the upper part of your AR in an M4 lower. But the thing is since the AR does not have a sear, the M4 will not be automatic.

Yes, AR-15 and M4 parts are interchangeable. Since the M4 is a variant of AR-15s, the parts are almost identical to fit in both rifles. The AR-15s are customizable, and most parts and ammunition of the M4 can be functional. However, there are very few differences and limitations when it comes to civilian guns and military weapons.

Yes, an M4 barrel will fit an AR-15. As we’ve said earlier, the M4 is a shorter version of AR-15 so that it can fit. However, since the M4 has a short barrel, it must secure an SBR tax and tons of paperwork to legalize owning one. In addition to this, you must ensure that the caliber is the same to avoid damage.

The Colt AR-15 is the closest rifle to the M4. Since the M4 is designed just like this type of rifle, some parts are identical, especially inner parts. At first glance, you may think that Colt AR-15 is an M4 with a shorter barrel, but the differences will be noticeable once used.

Yes, an MR lower is the same as an AR-15. The lower of the M4 are internally the same as AR-15. When you overhaul an AR-15, every single internal part of the lower receiver is the same and compatible with each other. M4 does have a semi-auto fire setting that AR-15s are only capable of since it is not a full-auto weapon.

M4 vs AR-15: Which is Better?

Based on our observation. M4 is better than the AR-15. As technology arises, more improvements on M4 made it more modern, functional, and reliable. It is the reason why the US Military adopted this military weapon instead of the M16. 

However, even if the M4 is better, civilians are not allowed to own the gun because it is a full-auto gun. But you can have the same version of these weapons with minimal difference. Buying and upgrading your AR-15 with shortened barrel and M4 handguards is the only way of having the same weapon minus the full auto.


  1. https://www.npr.org/2018/02/28/588861820/a-brief-history-of-the-ar-15

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