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!
Table of Contents
Loading…
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.”
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.
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:
- 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 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.
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.
Prices accurate at time of writing
Prices accurate at time of writing
-
25% off all OAKLEY products - OAKLEY25
Copied! Visit Merchant
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. 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.
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.
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.
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.
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.
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.
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.
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.
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.
39 Leave a Reply
Why are you spreading misinformation about AR-15s never being full-auto, when that's exactly what the AR-15 was designed to be?
As retired a Manufacturing Engineer I can tell you that the advantage of any of the .223/5.52 rifle/carbines are their modular design. You can replace the barrel of a AR-15 from carbine (14.5" to a 16" to 20" barrel) to make it a rifle. You can make military M-16 into a civilian AR-15 by removing the selective fire mode in the trigger group. There are over 50 variations you can assemble to make them personal firearms. Modularity is the term that most endears the AR styling.
This implies that a civilian can legally own a "Property of US Government" stamped M4 lower receiver, including the stamps for "safe/fire/burst" as long as the fire control group in specifically "semi-auto" only. True or false?
Are they magnum. Are they the same caliber. Is one a .30cal, is there a .30 cal version.
I have heard that they are magnum .22s with a MV of ~3,000 fps.
K.E. = 1/2MV**2.
A magnum .22 is a .22 magnum. 5.56 is way beyond that. The AR platform is just that; a platform ranging from shotguns to rifles in all gauges and calibers. So you can get an AR 12 gauge shotgun and you can get an AR rifle in many, many calibers small rimfire to large centerfire.
As prior military I can tell you the real differences between the AR15 and the M4 is: The AR15 (M16)A1 and A2 have a 20” barrel, iron sights with a carry handle and fixed buttstock. The A3 is the same with a 16” barrel and has a carry handle or pictinny top rail and a fixed buttstock. The A4 aka AR4 and M4 is the carbine version of the prior mentioned rifles. Carbine meaning it is shorter and lighter for the purposes of close quarters combat and paratroopers. The A4, AR4, M4 has a 14.5”-16” barrel, pictinny rails on the upper frame and handguards and an adjustable buttstock and I think cannot accommodate the 203 grenade launcher, but Im not 100% certain about that. The A1, 2, 3 versions can.
Because parts for these are all interchangeable you will see mixed variations of these everywhere.
I should mention that AR (Armalite Rifle) has come to be known as the civilian model of these rifles because of the semi auto only fire capability. The M (military) has full auto select fire: safe, semi, 3 round burst or full auto.
You can also obtain these rifles that use a gas piston to cycle the bolt instead of just gas being exhausted into the chamber which makes if get dirty and not function as well if not cleaned regulary.
And it decapitates kids in classrooms! What more could gun nutties want
Ooo here we go. Sorry dude guns don’t kill people. Dumbass people due that are looking for attention.
I have no dog in this fight since I'm Canadian and this is all a moot point for us. What I want to comment on instead is your butchery of the English language. Do you honestly not know the difference between "due" and "do"? This is primary school stuff. Early primary school, in fact. In case you failed grade three, I'm going to give you the Cliff's Notes on this "conundrum". "Due" is an adjective that implies an obligation, debt, or requirement, i.e. Due to inclement weather, the game was delayed. "Do" is a verb that refers to an action, i.e. I failed grade three, so I had to do it over again.
The available calibers of the M4 were not mentioned. Don’t they come in 308?
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.
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.
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 :-).
NOT select fire - Daniel Defense SOCOM-M4A1
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.
Colt also has the LE6940 and LE6920 which are called M4.
AR is an assault rifle, it's literally in the name - A(ssault)R(ifle)
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.
Did you not actually read the article? AR has NEVER stood for "assault rifle".
No.... AR stands for Armalite rifle!( Do your home work.)
Piotr M = Puts In Opinion That Relays Misinformation
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
It is amazing how many people who own guns think this... and then comment.
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
No...
GMC stands for Got Mechanic Coming
LOL
AR means "Armalite Rifle".
AR means "Armalite Rifle".
You’re not terribly bright are you???
AR does not stand for assault rifle
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 .
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
Great article! Thank you.
no mention of eugene stoner?
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!
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:
Awesome
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
Glad we could help!
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.
That’s what I thought