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M16 vs. M4 vs. AR15 - A1, A2, A3, or A4? Understanding the Different Types of AR15 Rifles

The AR15 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.

AR15 vs. M4 vs. M16 - What's the Difference?

To understand the different types of AR15's, you first need to start with a little history.

The AR-15 was a direct evolution of the AR-10, which was developed by Eugene Stoner in the 50's. The first ones were no more than simple 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 off the M16 rifle, which was eventually known as the M4 Carbine. The M4, which features a shorter barrel, collapsible stock, and other modifications, has become standard equipment for close-quarters combat through the US Military.

While the military still uses the M16 for some infantry applications, it is 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

You'll often hear people refer to the different types of AR15's as A1, A2, A3, or A4. These terms actually refer to the different generations of the M16 rifle, and they are often used incorrectly when referring to AR15'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 off from.

The A1, A2 and A3 have a permanently-attached carry handle and the A4 does not. Although the A4 has a removable carry handle option, it does not 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 is similar on all these models is the forward assist. It is a standard feature and is equipped in all the 4 types - A1, A2, A3 and A4. The forward assist was non-existent to the original incarnation of the M16 but is a necessary option 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 the same weapon.

The A4 may be referred to as the flat top version because of the removal of the carry handle and it distinguishes itself as the only one in the group ready to be equipped with an optic. 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 through the years, and the US Military has driven many improvements on the original AR15 platform. While all of these different changes can get a little confusing, the result has been improved weapons for both military and civilian use. 

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.
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3 comments

Ted Bernhardi

August 15, 2016

Thanks for the two explanations. I already knew this and mine are mil spec, but it’s very helpful and a nice review.

Bob Palmer

August 16, 2016

I believe the M4 has had the feed ramps re-configured to make feeding more positive. I have an AR15 A2 that I bought in 1980 about 12 years after returning from Viet Nam. I also have an M4. You can’t tell the difference by looking but take them both to the range and you can see the difference. If you run the A2 wet it functions well but the M4 runs wet, dry, or full of dirt and it will usually function. I built the M4 myself and I made sure all the tolerances were correct.

Andrew Krause

October 05, 2016

Point of clarification: the M4 absolutely did have a carry handle that came with the weapon. As correctly stated in paragraph 8, it was a removable carry handle that fit onto rail system. It was very similar in appearance to the A2 and A3 carry handle, though I believe the adjustments were finer. Finally, the A4 include the Knight’s Armaments rail system that allowed one of four panels to be field removable so that you could attach accessories. Also, the twist in the barrel was taken from the 1/12 considered optimal for the US M193 5.56mm cartridge to the 1/7 twist for NATO SS109 standard cartridges. There were also a LOT of changes to manufacturing methods that helped with reliability and operation in the field.

Would have loved to have included some mention of the CAR-15. The dramatic changes from the M16A2 to the M4A1 seen in pictures above are largely due to the militarized version of the CAR-15, designated the GUU-5P. The Army Special Operations community was still using these into the mid 1990’s, and they were employed by Delta Force (technically “Operational Detachment Delta”) operators during the Battle of Mogadishu.