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By Brad Steenrod

The AR platform has undergone many changes over the years, and it can be pretty confusing to the average gun-owner. The goal of this article is to help you keep it all straight.

AR-15 vs. M16 vs. M4 – What’s the Difference?

To understand the different types of AR platform rifles, you first need to start with a little history.

The .223/5.56 AR-15 rifle was a direct evolution of the 7.62×51 AR-10, which was developed by Eugene Stoner in the 1950’s. The first ones were no more than scaled-down versions of the AR-10.

In the late 1960’s, the US military began use of an AR-15 variant known as the M16 rifle. This rifle became standard equipment for the US Army beginning in the Vietnam War. The rifle has gone through several generations of improvements since the original model – we will explore these later in this article.

In the 1980’s, Colt began work on a new platform based on the M16A2 rifle, which was eventually known as the M4 Carbine. The M4, which features a shorter barrelcollapsible stock, and other modifications, has become standard equipment for close-quarters combat throughout the US Military.

While the military still uses the M16 for some infantry applications, it’s being phased out in favor of the M4, as the M4 offers distinct advantages in portability and maneuverability through its lighter weight and smaller dimensions.

A1, A2, A3 and A4 Similarities and Differences

A1, A2, A3 and A4 Similarities and Differences

You’ll often hear people refer to the different types of AR-15s as A1, A2, A3, or A4. These terms actually refer to the different generations of the M16 rifle, and they’re often used incorrectly when referring to AR-15’s.

So what are the differences between these different types of M16’s?

The carry handle is a big difference between models and is a good place to start.

The A1, A2, and A3 have a permanently-attached carry handle that the A4 doesn’t. Although the A4 has a removable carry handle option, it doesn’t look anything like the previous versions.

The A1 carry handle also featured the rear sight which had a tool-adjusted windage selector (a bullet tip could also be used to make the adjustments, and that’s what most soldiers would do).

One feature that’s similar to all these models is the rifle’s forward assist. It is a standard feature and is equipped in all the 4 types – A1, A2, A3, and A4. The forward assist can be used to make sure that the bolt is fully forward and locked.

The A2 and A3 went further on the idea and incorporated easy adjust windage and elevation selectors on their carry handle rear sight. These are all nonexistent features in the A4 with the carry handle having been removed from its design.

The A2 design featured several improvements over the A1, including a spent case deflector immediately behind the ejection port to prevent cases from striking left-handed users, a heavier barrel, and the modified action that replaced the fully-automatic setting with a three-round burst setting.

The A3 is so similar to the A2 that they are almost twins. The main difference between them is the fire-select feature on the A3. Other than that they are virtually the same rifle.

The A4 may be referred to as the flat top version because of the removal of the carry handle. It distinguishes itself as the only one in the group ready to be equipped with an optic. That’s very much unlike the A1, A2 or A3 which require an adapter to fit on optic on top of the handle.

To summarize, much has changed with these rifles through the years, and the US Military has driven many improvements on the original AR platform. While all of these various changes can get a little confusing, the result has been improved weapons for both military and civilian use.

Looking to build your first AR 15 or would love to upgrade? It’s easy and affordable with AT3 Tactical’s AR 15 Parts and Accessories.

One Last Tip

If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.


This article was originally published in AT3 Tactical AR Academy and is reprinted here with permission.  

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  1. Not to knock the article, but the best place for this type of info on AR platform is Chris Bartocci. The man is a walking encyclopedia for Stoner rifles.

    • The Stoner system was a great system, far better than the M-16 has ever been, still have a Stoner 7.62 x 51 mag carrier from my days as a Marine tester during that period, was really surprised that it was NOT accepted by the Marine Corps!

      • The Stoner system was tested in the desert by the Israelis and it was found to be unreliable under desert conditions.

  2. The M-4 was adapted because of the restricted dimensions of the Bradley IFV. The full length barrel M-16 was awkward to handle inside the vehicle. The Carbine has proven problematic in Afghanistan. The Mujahedeen often can engage US forces outside the effective range of the M-4. That is why the Army brought back the M-14 in the early days of the war.

    The AR platform was one of those off the shelf temporary solutions that lives on because there are other requirements to be met. I know it is heresy to speak ill of it but the AR platform chambered in 5.56 is inadequate as a primary infantry weapon. And if the Army had upgraded the weapon 30 years ago we wouldn’t be hearing about our ARs as weapons of war.

    • I’m sure we would, seeing as the people who call it a weapon of war would likely say the same thing about a 10/22 in a pistol grip stock. It would just make them look even dumber when they did it.

      Besides, if they replaced it with anything it probably would’ve just been a caliber conversion. The platform itself works just fine, even if the 5.56 is a little anemic for the job sometimes.

    • Using a .308 caliber full sized cartridge (or ANY full sized rifle cartridge) as a primary infantry weapon is dumb. Less ammunition capacity, significantly increased recoil, near uncontrollable in full auto, significantly heavier. Dumb dumb dumb.

      • You’re not taking into account where the combat might occur at. In mountainous terrane where the enemy is shooting at you at 700-800 meters away or in heavy jungle where a 5.56 round tends to fly off course after hitting a small branch or leaf, I sure would rather have an 7.62 NATO than I would a 5.56 round.

        • As I own both an AR-15 and an AR-10 and humped both extensively in the hills and woodlands of the Midwest while hunting. I can honestly say I would chose the AR-15 90% of the time. While the AR-10 has a distinct advantage in fire power. That firepower is not worth the extra weight of the weapon and lose of ammo due to weight. The one place an AR-10 holds the advantage would be in a static situation. Where the need to move over distance is unnecessary. One must keep in mind that every pound of added weight is compounded by sweat and fatigue at the end of the day

        • The idea of 5.56 deflecting in the jungle is completely over blown. Guys were missing and blaming the cartridge. Just like in Korea with the M1 Carbine. The Army tested out 5.56 in heavy foliage and found out the cartridge would deflect enough to miss at about 3 times the range you could see the target.

          And 5.56 is fine for Afghansitan. People are acting like we are losing firefights to belt fed machine guns and so need to upgrade our rifles. Simply not true. One, rarely are casualties sustained from long range harassing fires. Which is what it is. The Taliban bring a PKM or Dskh and set up up in a concealed position. Fire off a belt or two. Than bounce before effective fire and cas can be brought to bear. The majority of US troops killed by small arms are still killed at intermediate cartridge ranges.

          And what people don’t want to hear is. We could give everyone 6.5 creedmores. And the vast majority of troops can’t take advantage of the round. Trying to make hits at 200 yards when being shot at isn’t easy. Much less at 600 yards plus. We should be pushing down smart munitions like the switchblade and relaxing ROEs to actually allow are heavy weapons like mortars into the fight.

      • Even before the Vietnam War ended the Army figured out that full auto is dumb, dumb dumb. If someone had bothered to actually take a critical look at Marshall’s analysis in the 60s they would have probably fixed the problems with the M-14. Full auto is rarely used. The three round burst setting is used for suppression. If you were to used it exclusively you have fewer units of fire than a WWII infantryman.

        • The problems were attributed to poor quality control not its basic design. Springfield’s M-1A is an excellent rifle.

        • Yes the M14s design is still bad. It’s outclassed by the AR10/15 in every way. The M14 is just a improved Garand. Essentially a 1920s design. I don’t get how people still try and defend the gun with as much of its history and performance being open source.

    • The first generation of M-2 Bradley Fighting Vehicles (BFV) fielded in 1981 had 6 gun ports that mounted the M231 Firing Port Weapon (FPW). These M-2 BFV initially deployed in West Germany to Armor and Infantry Divisions and stateside divisions that would head to Europe during wartime. The M231 FPW was a pretty cool idea at the time, but the 6 gun ports and M231 FPW were eventually eliminated due to changes in the the M-2/A1 BFV with add on armor or up armor of different types available at that time in the early and mid to late 1980’s. The M231 FPW was derivative of the M16A1 rifle. The barrel length of the M231 FPW changed from 11 inches initially to approximately 16 inches in the final version to better support the ballistics of the 5.56x45mm 55gr M193 cartridge. The M231 FPW had no buttstock, no sights, and had only two modes of firing safe and fully automatic.

  3. So, if the A-3 has a permanently affixed rear sight / carry handle and is virtually identical to the A-2…where is it in the photo of the (supposed) A-3?

    • It could be that first one and you wouldn’t know. :^)

      The A3 is completely identical to the A2 except it has a full-auto trigger group instead of a 3-round burst group. Later on, the Navy and Colt changed them to flat-top A4 uppers, but now they’ve been replaced by M4A1s.

    • Admittedly, it is confusing that there is no separate photo of an A3, but the picture of an A2 will suffice for it; An A2 has a 2~3-round burst internal mechanism (I think that that is technically called ‘semi-full-auto’/sarc) whereas an A3 has full-full-auto internal bits as in the original and A1 versions. Other than that, they are identical.
      The last photograph is of an A4.

  4. I remember using a cartridge to fiddle with my sights, front and rear. Full auto was not really anything but an ammo waster. Fun. But not really needed. And with the 20 round mags full auto was kinda quick.

    I think I may have used an ar15 maybe twice in the 40+ years since I left the service. It just does nothing for me.

    • AND we only loaded the 20 round mags with 18 rounds due to feeding issues. FYI, it took 1 1/2 seconds to empty a mag on rock ‘n roll.

  5. Good article. Some difference that were missed in this part are the following below.
    The M16 family of rifles had a 20 inch barrel length with a rifle length gas port system. All M16A1, M16A2, M16A3, and M16A4s rifles can mount under barrel 40 mm grenade launchers, such as the M203 and M320. All M16 family of rifles can use the 20 and 30 round detachable magazines. The M16 initially used a 20 round detachable magazine and in 1967 the 30 round detachable magazine slowly replaced 20 round detachable magazines as the standard magazine used with the M16 family of rifles in all of the services.

    The ArmaLite AR-15, referred to as the XM16, was the early designation of the rifle tested and used by the U.S. Air Force in the early 1960’s in Vietnam. The AR-15 had numerous modifications completed at the request of the U.S. Air Force and U.S. Army. But the main modification was the relocation of the charging handle from the center of the carrying handle like on the AR-10 to a new location on the rear of the upper receiver. The new rifle was referred to as the XM16E1 by the U.S. Army in 1963 and the M16 by the U.S. Air Force. The XM16E1 was later modified in numerous ways that included a chrome plated chamber and bore, chrome lined barrel, and a forward assist that was request of the U.S. Army after issued arose from corrosion and stuck cartridges in XM16E1 rifles in Vietnam. After these numerous modifications, the XM16E1 was referred to as the M16A1 rifle in 1967.

    XM16E1 and M16 rifles had the safe, semi-automatic, and fully automatic firing modes. The M16 used a rifle length triangular shaped fiberglass two piece handguard. Muzzle device was initially a flash suppressor design with three tines or prongs. Used the 20 round detachable magazine. Chambered in the 5.56×45mm used the 55gr M193 cartiage with a 1:12 barrel twist with a light weight pencil barrel. 300 meters effective range.

    M16A1, from 1967 to 1987, had the safe, semi-automatic, and fully automatic firing modes. Chambered in the 5.56×45mm used the 55gr M193 cartridge with a 1:12 barrel twist with a light weight pencil barrel. The M16A1 used a rifle length triangular shaped fiberglass and later on polymer two piece handguard with heat shield. Used the 30 round detachable magazine. Muzzle device was later changed to the A1 bird cage flash suppressor on the M16A1 due to the problems encountered in the jungles of Vietnam. 300 meters effective range.

    M16A2, from 1983 to had the safe, semi-automatic, and 3-round burst firing modes. Chambered in 5.56×45mm NATO used the 62gr SS109/M855 cartridge with a 1:7 barrel twist with a government profile heavier barrel. The M16A2 used a rifle length fat round shaped two piece ribbed polymer handguard with heat shield. Used the 30 round detachable magazine. Muzzle device was changed to the A2 style muzzle brake with the 2 bottom ports eliminated from the A1 flash suppressor to reduce muzzle climb and prevent dust from rising when the rifle was fired in the prone position. M16A2 upper receiver had a fully adjustable rear sight with a 600 meter effective range.

    M16A3 had the safe, semi-automatic, and fully automatic firing modes like the M16A1. Chambered in 5.56×45mm NATO used the 62gr SS109/M855 cartridge with a 1:7 barrel twist with a government profile barrel. The M16A3 used a rifle length fat round shaped two piece ribbed polymer handguard with heat shield. Used the 30 round standard magazine.Used the 30 round detachable magazine. A2 style muzzle brake. M16A3 upper receiver had a fully adjustable rear sight with a 600 meter effective range.

    M16A4 have the safe, semi-automatic, and 3-round burst firing modes like the M16A2. The M16A4 upper receiver uses a flat top Picatinny rail system. The M16A4 rifle use a 12 inch rifle length two piece handguard with a quad Picatinny rail system for mounting optics and other ancillary devices. The M16A4 with the flat top upper receiver and full length quad rail system was also known as the M16A4 MWS (Modular Weapon System). Uses the 30 round detachable magazine. Chambered in 5.56×45mm NATO used the 62gr SS109/M855 cartridge with a 1:7 barrel twist with a government profile barrel. Uses the 30 round standard magazine. A2 style muzzle brake. M16A4 has a 600 meter effective range.

    All of the M4 family of rifles have a 14.5 inch barrel length with a carbine length gas port system. The M4 and M4A1 rifles have a flat top Picatinny rail upper receivers. The M4 and M4A1 rifles use a 7 inch carbine length two piece handguard with a quad Picatinny rail system for mounting optics and other ancillary devices.

    M4 rifles have the safe, semi-automatic, and 3-round burst firing modes like the M16A2 and M16A4s. Chambered in 5.56×45mm NATO used the 62gr SS109/M855/M855A1 cartridge with a 1:7 barrel twist with the 14.5 inch carbine length government profile barrel. Uses the 30 round detachable magazine. A2 style muzzle brake.

    M4A1 rifles have the safe, semi-automatic, and fully automatic firing modes like the M16A1 and M16A3. Chambered in 5.56×45mm NATO used the 62gr SS109/M855/M855A1 cartridge with a 1:7 barrel twist with the 14.5 inch carbine length government profile barrel. Uses the 30 round detachable magazine. A2 style muzzle brake.

    • Your post is getting into the kind details that most people don’t care about. I can see why they would not be included in the main article…
      But they were what I was expecting to read, so thanks!
      The past year or two I’ve been getting into more of the technical details because I’ve been building more than a few of my own rifles. One of these days I’ll just start buying (even more) real books on the subject and jam even more torque specs, twist rates, powder types etc into my head.

    • J, you are correct about the effective range of the M16A2, A3, and A4 as being 600 meters.
      However, you are wrong about the M16 and M16A1 having an effective range of only 300 meters.
      The correct effective range for the M16 and M16A1 is 460 meters.
      The 62 grain bullet and 1:7 twist of the M16A2 did not, I repeat NOT, double the range of the 55 grain bullet in the 1:12 twist barrel of the M16A1, and it’s inconceivable that it would double the range.

      I served in the U.S. Army when both the M16A1 was in service, and the M16A2 was just coming into service, so the Army’s firearms instructors taught us the difference.
      In the Army, I qualified as on the M16A1 as an EXPERT shot. It wasn’t easy to qualify as expert with the M16A1, with its pencil barrel and iron sights, by the way. The M16A1 qualification course included targets at 300 meters, and I hit every single target at 300 meters (which was well within the M16A1’s effective range of 460 meters. Yes, 460 meters, not 300).
      The M16A1 effective range was 460 meters, and you don’t need to dig up an Army field manual from 1984 to prove it; just Google it.

  6. As for the latest “scare words” from the left about the AR15 being a “military grade firearm” then I reply….

    The typical semi-auto AR15 bought at the corner gun store has never been fielded by a front line combat military force by any nation. Ever.

    • Thank you for clarifying that 🙂
      I have wondered whether Biden shipped mail order AR15 semiauto Weapons Of War to Ukraine. You know, the ones that can blow a lung right out of your body. It is so embarrassing.

  7. “They are all black and scary and frighten little children, especially the ones with the shoulder thing that goes up.” said some snowflake politician somewhere (LMFAO)

  8. Its interesting to note that on the web site Forgotten Weapons there was a mud test where the M16 with its smaller ejection port was more reliable than the AK 47 also tested. Of course it gets more complicated than this simple test. The M16 to this very day still sprays burnt powder all over the action and under rainy conditions or the lack of cleaning it will jam up long before the AK 47 does. So all this just adds more fuel to the controversy as to which is the better weapon.

    • There really isn’t much left to debate. The AR has proven itself a more ergonomic weapon with better accuracy potential than the AK. On the other hand the AK has proven itself to be more reliable and effective than the AR, in the hands of an only minimally trained force.
      The AR requires more care and knowledge to wring out all of its capabilities, and the AK was designed for harsh Russian conditions and barely trained recruits. Both reign supreme in their individual castles. If I had to train a group of natives that barely speak English in some jungle backwater, I would sure rather train them to use an AK than an AR. On the other hand if I was leading a team of special forces who know what the hell they’re doing, I’d rather they had ARs. Actually, I’d probably want to outfit each of these individually, since logistics won’t enter into that situation.

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