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[What’s the Difference?]: AR-15 vs M4

Want to know the difference between the AR15 for civilians and the military M4? We cover that plus a little history, similarities, and the best for you.

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?

Upgraded AR-15s
Upgraded AR-15s

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.

AR-15 with Omega 300
AR-15 with Omega 300

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!

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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 U.S. Continental Army Command for a 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.”

Imagine replacing all these circled weapons plus the Tommy Gun with just one rifle.
Imagine replacing all these circled weapons plus the Tommy Gun with just one rifle.

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 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.

Early AR-15s
Early AR-15s

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. Unfortunately, he would continue to be shot down.

Until 1963, that is…

U.S. Secretary of Defense Robert McNamara was almost a decade into the Vietnam War and had to face three facts:

  1. The M14 could not compete with the enemy’s AK-47.
  2. The AR-15 consistently outperformed both the M14 and the AK-47 in testing.
  3. M14 production simply couldn’t meet the demands of the U.S. 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. It quickly gained popularity. When Colt’s patent on the rifle expired in 1977, other manufacturers quickly began selling their own versions.

Faxon Firearms Ascent AR-15
Faxon Firearms Ascent AR-15

These days, just about every firearms manufacturer has its own AR-15 style rifle. And a huge market exists for AR-15 parts and accessories due to the rifle’s modular design.

646
at Palmetto State Armory

Prices accurate at time of writing

Prices accurate at time of writing

Available Coupons

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. 

Colt Commando
Colt Commando

The Commando did the job, but it had some issues with range and accuracy due to the shortened barrel. Therefore, in 1984, Colt began the development of the XM4.

Its 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 a new naming convention — M4. It was eventually adopted by the U.S. military in 1994.

M4 Carbine
M4 Carbine

Both the M4 and the M16 (now up to the M16A4 model) still serve soldiers today. And the M16 remains the longest continuously serving rifle in U.S. 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 occupy the same family. So, it 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.

Colt M16A2
Colt M16A2

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. That means it offers a smaller 14.5-inch barrel. The standard AR-15 barrel measures 16 inches.

Even More AR-15 Uppers
Even More AR-15 Uppers

With so many different versions and such a large market for AR-15 upgrades, longer barrels can also be found. Remember, though, that U.S. 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.

M4 Carbine with M203 Grenade Launcher
M4 Carbine with M203 Grenade Launcher

In proportion with the shorter barrel, the M4 has a shorter gas tube. To compensate for the shorter gas tube, the M4 also has modified feed ramps.

The M4 features a collapsible stock, while the standard AR-15 opts for a fixed stock. that said, collapsible stock configurations are widely available for the AR-15.

Adjustable AR-15 Buttstocks
Adjustable AR-15 Buttstocks

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 a 3-round burst or fully automatic.

Similarities

The similarities lie in basically everything else.

The bolt carrier group, charging handle, and trigger assembly are all the same. Each guns’ internal parts of both the upper and lower receivers remain virtually identical.

And the few discrepancies exist in 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. The M4 is only available for use by military personnel.

Putting on that Uniform Is the Only Way You’ll get to shoot a real M4.
Putting on that uniform is the only way you’ll get to shoot a real M4.

Don’t sweat it too much, though, because the AR-15 is virtually the same gun without the fully automatic capabilities. Not to mention, options exist for making it even more similar.

The easiest and most accessible way is to buy a mil-spec lower and M4 handguards. These are 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. 

Full auto Sp01
Full auto SP-01, sold at Rock Island Auction for $34,500

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.

Conclusion

So, to sum everything up, the AR-15 is essentially a semi-auto, civilian version of the M4. On the other hand, the M4 offers full-auto capabilities.

Lead Star Grunt AR-15 (12)

Unless you’re military, you probably won’t be able to keep an M4 in your safe but AR-15s are readily available and customizable. So, it’s hardly a loss at the end of the day.

What do you think about the M4? Let us know in the comments below. Looking for other ways to upgrade your AR-15? Then check out our guide to AR-15 upgrades and accessories.

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28 Leave a Reply

  • Commenter Avatar
    Jon Tice

    Not entirely true. I bought a genuine Colt M4 (without selective fire of course), from my local gun store. Even has the barrel cut-out for the M203. Shoots beautifully.

    June 26, 2022 10:40 am
  • Commenter Avatar
    Cameron

    Thank you for specifying this. Politicians who may have served at some point (though were probably remf, probably 92A) keep holding up AR-15s and claiming that's what they went to the sandbox with. And people who don't know better keep eating it up. I'd rather have accurate information thrown up to contradict the disinformation posted everywhere.

    June 16, 2022 4:01 am
  • Commenter Avatar
    Eric

    Like the M-16A2, the original M-4 selective fire capability was Safe/Semi/Burst. The M-4A1 is Safe/Semi/Auto. M-16 and M-16A1 also were Safe/Semi/Auto. I carried an M-16A1, M-16A2, and M-4 while in the Army :-).

    March 7, 2022 1:49 pm
  • Commenter Avatar
    charlie romeo 2591

    NOT select fire - Daniel Defense SOCOM-M4A1

    December 25, 2021 3:30 am
  • Commenter Avatar
    Andrew James Hodges

    I am going to disagree with one point. Just as all squares are rectangles but not all rectangles are squares, all M4s and M16s are AR-15s but not all AR15s are M4s or M16s. Only a small fraction of all the AR15s that exist are select fire/machine guns (I would estimate less than 5%) and the vast majority of those are in possession of military and law enforcement.

    December 24, 2021 9:47 am
  • Commenter Avatar
    Mike

    Colt also has the LE6940 and LE6920 which are called M4.

    November 25, 2021 7:31 am
  • Commenter Avatar
    Piotr M

    AR is an assault rifle, it's literally in the name - A(ssault)R(ifle)

    November 11, 2021 11:43 am
    • Commenter Avatar
      Jacki Billings, Editor

      Hey Piotr, that's a common misunderstanding that unfortunately gets inaccurately repeated. AR is NOT short for assault rifle. In truth, AR stands for Armalite Rifle. Armalite was the company that developed the AR-15.

      November 11, 2021 2:27 pm
    • Commenter Avatar
      Bob

      Did you not actually read the article? AR has NEVER stood for "assault rifle".

      November 26, 2021 2:52 pm
    • Commenter Avatar
      Thomas Daly

      No.... AR stands for Armalite rifle!( Do your home work.)

      December 23, 2021 3:32 am
    • Commenter Avatar
      Richard V Childs

      Piotr M = Puts In Opinion That Relays Misinformation

      December 24, 2021 6:46 pm
    • Commenter Avatar
      joe mama

      your dumb ar mean ArmaLite model 15. anything can be considered an assault, assault stick. a rifle is a tool and by itself its harmless. its the system that is screwed. not the gun. its all a way for the government to steal rights away from its citizens

      January 24, 2022 2:23 am
    • Commenter Avatar
      Robbie Taylor

      It is amazing how many people who own guns think this... and then comment.

      April 5, 2022 4:56 am
    • Commenter Avatar
      Vincent

      PIOTR…
      People
      Ignorant
      Of
      The
      rifle
      “It’s literally in the name” WOW your clueless
      I suppose GMC stand for guys molest children
      STFU when you dont know shit

      June 3, 2022 6:37 pm
    • Commenter Avatar
      RC

      AR means "Armalite Rifle".

      June 8, 2022 1:26 pm
    • Commenter Avatar
      RCarl

      AR means "Armalite Rifle".

      June 8, 2022 1:27 pm
    • Commenter Avatar
      Jon Tice

      You’re not terribly bright are you???

      June 26, 2022 10:41 am
  • Commenter Avatar
    jon arbuckle

    Forgot to mention that in the 90's Colt discontinued millling out the upper shelf behind the sear which prevents the installation of
    drop-in precision and binary triggers .

    June 27, 2021 6:26 am
    • Commenter Avatar
      Joseph M Mcginnis

      That was to prevent the installation of auto sears, not to prevent a drop in trigger, a 2 stage trigger or a binary trigger. Please learn before replying with misinformation

      December 26, 2021 4:22 pm
  • Commenter Avatar
    Liliya B.

    Great article! Thank you.

    August 18, 2020 10:23 pm
  • Commenter Avatar
    travis v lopez

    no mention of eugene stoner?

    August 2, 2020 9:05 am
  • Commenter Avatar
    Anthony Musselman

    Awesome article! I shot the m-4 for years in the military and just now was like... well... what the hell even is the m-4?

    Thanks for the awesome explanation!

    July 26, 2020 1:52 pm
  • Commenter Avatar
    Gregg

    In 1963 the u.s. involvement in vietnam was limited to advisors and not a full military operation. This paragraph from the above article is in error.
    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:

    July 20, 2020 10:55 am
  • Commenter Avatar
    Steve

    Awesome

    September 15, 2019 7:35 pm
  • Commenter Avatar
    DeserKeylon

    Thank you for all the information. I am looking to build my first weapon and this gives a good background and details as to why this gun is so popular.
    Thanks again

    July 14, 2019 7:10 am
    • Commenter Avatar
      David, PPT Editor

      Glad we could help!

      July 14, 2019 7:14 am
  • Commenter Avatar
    POGO

    The standard M4's fire selector is SAFE, SEMI, AUTO. Auto is 3 round burst there is no full auto except on the M4A1 that is used by special operations.

    May 1, 2019 4:27 pm
    • Commenter Avatar
      djnaldooo

      That’s what I thought

      February 23, 2020 5:57 am
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