You hear a lot about the M4 and especially the AR-15–both in the firearms community and in the news–but have you ever wondered what the differences are between them?
At first glance, these two rifles seem virtually identical. The truth is they are very similar, so there’s a lot of confusion about what differentiates them.
Simply put, the difference between the two is the M4 has either a full-auto or burst fire mode while the AR-15 does not. There are also minor differences such as barrel length and attachments, but these do not fundamentally affect the rifle.
We’re going to talk about the histories and differences of the M4 and AR-15 so that you can differentiate between these two fantastic rifles–and correct your friends when they use the names wrong.
Let’s dig in!
Origins of the Rifles
To start, let’s talk a little bit about the history of these two rifles to get a sense of their purpose.
History of the AR-15
The AR-15 was first designed in 1956 by Armalite as a scaled-down version of the AR-10. The “AR” in AR-15 stands for Armalite Rifle, while “15” is a model number. It doesn’t actually stand for “assault rifle,” which is a popular misconception.
The AR-15 was designed in response to a request by the CONARC (U.S. Continental Army Command) for smaller .223 rifle to test that could replace, all in a single rifle, the Browning Automatic Rifle, M1 Garand, M1 Carbine, Thompson Submachine Gun, and M3 “Grease Gun.”
Unfortunately, the rifle was nixed in favor of the M14, despite the fact that the AR-15 performed far better in testing.
As a very small company, that setback–combined with limited funds and production capacity–led Armalite to sell the AR-15 (along with its predecessor, the AR-10) to Colt just a few years later in 1959.
Colt made some improvements on the design, then began mass producing the rifle and pitching it to military organizations.
The Colt AR-15 quickly began to see success in small markets. After seeing a demonstration of the rifle in 1960, General Curtis LeMay, at that time Vice Chief of Staff of the U.S. Air Force, ordered 8,500 for Air Force pilots to use as survival rifles.
LeMay would continue to champion the rifle in the US military, even attempting to order 80,000 units in 1961 after being promoted to Chief of Staff of the Air Force, but would continue to be shot down.
Until 1963, that is. The US Secretary of Defense, Robert McNamara, was almost a decade into the Vietnam War and had to face three facts:
- The M14 could not compete with the enemy’s AK-47
- The AR-15 consistently outperformed both the M14 and the AK-47 in testing
- M14 production simply couldn’t meet the demands of the US Military
McNamara approved the rifle and it was adopted as the M16 (or as the M16A1 or XM16E1 for the variant with forward assist).
The semi-automatic version of the Colt AR-15 for civilian and police use hit store shelves in 1964, where it quickly gained popularity. When Colt’s patent on the rifle expired in 1977, other manufacturers quickly began selling their own versions.
These days, just about every firearms manufacturer has their own AR-15 style rifle and there’s a huge market for AR-15 parts and accessories due to the rifle’s modular design.
History of the M4
The history of the M4 builds on that of the AR-15 and M16, so there’s not as much to say here.
After the M16 was adopted, the military quickly demanded a carbine version for close quarters combat, so Colt began producing the Colt Commando XM177 in 1966.
The Commando did the job, but it had some issues with range and accuracy due to the shortened barrel, so in 1984, Colt began development of the XM4. Their goal was to combine the advantages of the Commando and of the new, improved M16 design, the M16A2, into the same carbine.
The XM4 underwent a decade of testing and modifications, as well as being renamed to the M4, before it was adopted by the US military in 1994.
Both the M4 and the M16 (now up to the M16A4 model) are still in service today, and the M16 is the longest continuously serving rifle in US military history.
So now that you’ve got a feel for where these rifles come from, let’s move on to the real reason you’re here: what makes the M4 and AR-15 similar and different?
Differences Between the AR-15 and M4
As we’ve seen, the AR-15 and M4 are in the same family, so it’s shouldn’t come as a surprise that there are very few differences between the two rifles.
You often hear the M4 described as the military version of the civilian AR-15 and vice versa, but that’s not really accurate. In reality, the M4 is the carbine version of the M16, the real military version of the AR-15.
If these rifles were a real family, then the AR-15 is more like an uncle, with the M16 being the AR-15’s brother and the father of the M4.
But what does that mean for the actual differences between the designs of the two guns?
For one, the M4 is a carbine-length rifle, so it has a smaller, 14.5-inch barrel, but the standard AR-15 barrel is 16 inches.
With so many different versions and such a large market for AR-15 upgrades, longer barrels can also be found, but US laws on short barreled rifles place a 16-inch minimum on barrel length on civilian weapons.
As a military weapon, the M4’s barrel can also be mounted with a grenade launcher thanks to a cut out in the barrel.
In proportion with the shorter barrel, the M4 has a shorter gas tube and to compensate for the shorter gas tube, the M4 also has modified feed ramps.
The M4 has a collapsible stock, while the standard AR-15 has a fixed stock–but collapsible stock configurations are widely available for the AR-15.
Finally, the primary, and best known, difference between the AR-15 and M4 lies in selective fire capabilities: the AR-15 is semi-auto while M4 can be fired in either three round burst or fully automatic firing options.
The similarities are basically everything else.
The bolt carrier group, charging handle, and trigger assembly are all the same. The internal parts of both the upper and lower receivers are virtually identical, and the few discrepancies are those required for the differences discussed above.
Depending on the configuration of the AR-15, even the handguards and rail systems can be the same.
M4 vs. AR-15: Which is Better?
Unless you join the military or are already serving (and if the latter, then thank you!), then you’ll have to settle for the AR-15 as the M4 is only available for use by military personnel.
Don’t sweat it too much, though, because the AR-15 is virtually the same gun without the fully automatic capabilities, and there are some options for making it even more similar.
The easiest and most accessible way is to buy a mil-spec lower and M4 handguards, which are both easy to find, and upgrade your AR-15 with them.
Under federal law you can also purchase or create an AR-15 with an M4 length barrel–assuming you fill out the correct form, pass the NFA background check, and purchase the $200 tax stamp.
You can even have a fully automatic AR-15, but this is considerably more difficult and expensive. For a fully automatic weapon to be civilian legal, it has to have been produced before 1986. Fully automatic AR-15s that meet this requirement do exist, but they’re relatively rare and in very high demand.
Getting one can easily set you back $14,000. Though I guess, in context, the NFA background check and addition tax stamp that is also required don’t seem so bad.
Looking for other ways to upgrade your AR-15? Then check out our guide to AR-15 upgrades and accessories, and don’t forget to share your questions and thoughts with me in the comments.