The AR-15 rifle is one of the most popular modern rifles used and owned worldwide, with an estimation of around 8-million within the U.S. alone. The firearm is extremely versatile, and with so many options to choose from, it can be a little overwhelming. We’re going to break down the basics for you, and if you are a new buyer, hopefully point you in the right direction.

So why is the AR-15 so popular, and what makes it so desirable over its counterparts?

Aside from the rifles extremely rugged impression, it is an excellent performer within its weight category. The AR-15 is highly accurate, lightweight, reliable, simple to use, cost-effective, has very little recoil, and is remarkably modular; it is immensely customisable to align with the shooter’s needs.

Understanding the AR-15’s unique features and its intended use not only increases knowledge, but more importantly increases the shooter’s ability to effectively use the rifle for what it was designed to do.

We are going to discuss the following in further detail.

• What is an AR-15?
• A Very Brief History on the AR-15
• The Advantages of an AR-15
• The Carbine vs. Rifle Length
• Which is Better: a Short or Long Barrel?
• The Mid Length vs. Rifle Length vs. Carbine Length Gas System
• Direct Impingement or Gas Piston?
• What is the Ideal Barrel Twist for an AR-15?
• Chrome-Moly vs. Chrome Lined vs. Stainless Steel Barrels
• The 5.56mm Fragmentation Range
• Does the AR-15 make a good DMR?

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First off, What is an AR-15?

The AR-15 is a lightweight semi-automatic rifle which fires the 5.56x45mm NATO or .223 Remington cartridge, and comes standard with a 30-round box magazine.

The rifle is often confused with M16 or M4 Carbine, so let’s take a minute to explain the difference.

• AR-15 – this is the civilian counterpart to the M16; a semi-automatic rifle. Barrel lengths vary, typically between 14.5 and 20-inches. Modern AR-15’s are far more modular than the original M16.

• M16 – the military version of the AR-15, which comes with a 20-inch barrel and is capable of firing in semi-automatic, fully-automatic, and 3-rounds bursts (version dependant).

• M4 – the carbine version of the M16 military rifle, with a shortened 14.5-inch barrel and a telescopic stock, capable of firing in semi-automatic, fully-automatic, and 3-rounds bursts (version dependant).

The main difference between the civilian AR-15 and the military M16 and M4 Carbine, is that that AR-15 is a semi-automatic only rifle and does not have the automatic fire capability.

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INTERESTING FACT:

Contrary to common belief, AR-15 does not stand for “Automatic Rifle” or “Assault Rifle” but instead it stands for “ArmaLite Rifle” after the company that developed it in the 1950’s

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A Very Brief History on the AR-15

• 1956 – the AR-15, or ArmaLite Rifle Model 15 was designed by Eugene Stoner, Robert Fremont, and L. James Sullivan of the Fairchild ArmaLite corporation.

• 1959 – the AR-15 trademark and its design was sold to Colt’s Manufacturing Company.

• 1964 – Colt then went onto selling its own improved version known as the Colt AR-15. For this reason, many people wrongly believe the rifle to have been designed by Colt.

• 1963 – the U.S. military selected Colt to manufacture the M16 automatic rifle that was released in 1964, and soon became standard issue for U.S. troops in the Vietnam War. The M16 was basically a fully-automatic capable version of the AR-15.

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So What are the Advantages of an AR-15 Over Something Else?

There are a number of features that give the AR-15 its uniqueness. These are often compared against the rifle’s biggest rival; the AK-47.

Accuracy

The rifle is renowned for its accuracy, with higher-end models achieving sub-MOA groupings, and entry level models commonly capable of 1.5-MOA groups. The rifle’s design naturally lends itself to consistency, making it an anomaly in the semiautomatic rifle world.

Effective Range

With an effective range averaging 600 meters, the rifle can outshoot its competitors, even capable of accurate 1000 meter shots given the right bullet, rate of twist, and shooter of course.

Recoil

One of the biggest advantages to the AR-15 is its recoil management, thanks to the rifle’s buffer system. Even shooters of small stature like women don’t have issues with the AR-15’s recoil. Many people admit to it being one of their favourite rifles to shoot.

High Ergonomics

The ability to customise and completely personalise the AR15 makes it one of the most modular rifles available. There is very little that the AR15 can’t do. If you want to make an AR-15 completely unique, DIY customisation is easy to achieve.

Handiness

Everything on the rifle has been designed for speed and ease of use. The light weight and comfort makes speedy target acquisition almost effortless, while the positioning of the safety selector and magazine release catch gives you an edge in speed over the rifle’s competitors.

Reliability

This one has potential to stir up a little debate, but the modern AR-15 is a highly reliable rifle, period. In order to keep reliability status with an AR-15, the rifle must be correctly maintained and the bolt carrier group (BCG) should run wet, particularly for direct gas impingement systems. This simply means lubing up the BCG; the dirtier the BCG gets, the more necessary lubricant becomes. If you are still unsure about the AR-15’s reliability, watch the video below.

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INTERESTING FACT:

Colt initially issued the M16 rifle to troops in Vietnam without cleaning kits, claiming that the rifle was self-cleaning. This led to numerous malfunctions and founded the myth which stated that the rifle was unreliable

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The AR-15 Carbine vs. Rifle Length

A large deciding factor to any new buyer is whether to go for the shortened carbine length, or the full-sized rifle version. While the standard carbine length has a 14.5-inch barrel, the rifle length sits at 20-inches, with 16 and 18-inch variants in-between.

In order to make the best informed decision, it would be a good idea to first understand the differences between the shorter and longer barrel, as well as the length of the rifle’s gas system. We will discuss this next.

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Which is Better: a Short Barrel or a Long Barrel

With both having their own advantages, it is difficult to say which is best; this really comes down to your own preference and intended use.

While the shorter barrel is more rigid, lighter, easier to conceal and offers enhanced manoeuvrability, the longer barrel offers a reduction in felt recoil, jump angle, muzzle blast and also increases the rifle’s effective range.

For more information between the two read our in-depth comparison titled: Is a Longer Rifle Barrel more Accurate?

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The Mid Length vs. Rifle Length vs. Carbine Length Gas System

The length of the gas system in direct impingement (DI) operated AR-15’s, which we will discuss shortly, should typically increase as the barrel length increases.

This is because if there is too much barrel length after the gas port, then too much gas flows into the receiver, which will likely cause issues with excessive recoil and accelerated wear on the rifle. But if there is not enough barrel length after the gas port, then too little gas flows into the receiver and the rifle may not cycle correctly resulting in a malfunction.

https://www.youtube.com/watch?v=N9YbHMzLuq8

The table below indicates the ideal gas system length for a given barrel.

Gas System	Barrel Length
Pistol Length	Less than 10-inches
Carbine Length	10 to 14.5-inches
Mid Length	16 to 18-inches
Intermediate Length	18-inches
Rifle Length	18 to 20-inches

While the decision on gas system length can often be ignored when purchasing a complete rifle from a reputable manufacturer, it is a good idea to understand how it works, particularly if you’re interested in a short-barrelled AR-15. I have known a number of friends who have purchased 11.5-inch barrels or shorter, and have found the rifles to be extremely fussy with ammunition.

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Direct Impingement or Piston-Driven AR’s?

We’re now talking about how the rifle uses gases generated by the burning propellant to cycle the action, giving your semi-automatic cycling capability. In other words, how the rifle is able to repeatedly load a fresh cartridge into the chamber by itself.

Direct Impingement (DI)

• This is the most common and original design found in the AR-15.
• Propellant gas is bled through a small hole in the barrel, which is then channeled through a thin tube where it directly contacts (or impinges) the bolt carrier group (BCG). This forces the BCG rearwards and cycles the action, chambering a new cartridge.
• The system is often considered to be more accurate than piston-driven rifles, but requires frequent cleaning as the bolt carrier group gets covered in carbon fouling from the dirty gasses.

Gas Piston

• Propellant gas is bled through a small hole in the barrel, however instead of being forced into a tube as it is in a direct impingement system, it is contained in a separate cylinder.
• This cylinder contains a piston that forces the BCG rearward to handle the extraction and ejection process.
• The gas-driven system is often more expensive than DI, but the advantage is that the rifle runs much cleaner.

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What is the Ideal Barrel Twist for an AR-15?

Selecting the best rate of twist to suit the bullet which you intend on shooting can be vital, ensuring most efficient bullet stability during free flight.

The original M16 rifle had a 1:12 twist, meaning that bullet completes one full revolution for every 12-inches of barrel. This was the ideal twist rate to stabilise the 55-grain bullet used by the M16. However, modern AR-15’s come with faster twist rates, allowing the shooter to use heavier bullets with superior terminal ballistics.

• 1:9 Twist – this is best for stabilising lighter and mid-weight bullets up to around 69-grains.
• 1:8 Twist – probably the most versatile twist rate found amongst AR-15 rifles.
• 1:7 Twist – the twist rate chosen for modern military AR-15’s and the M4 Carbine. Designed to shoot heavier bullets.

So which twist rate is best?

A 1:9 is very common amongst AR-15 owners, and will shoot the majority of bullets up to 69-grain very well. However, is you intend on pushing your rifle’s effective range to its limits, then you’ll want a 1:8 or 1:7 twist rate to shoot heavier VLD (very low drag) bullets such as the Hornady 73-grain ELD Match bullet.

Use this Twist Rate Stability Calculator by Berger to determine if a specific bullet will stabilise in your barrel.

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Chrome-Moly vs. Chrome Lined vs. Stainless Steel

AR-15 barrels come in a number of finishes, with some proving to be more advantageous over others.

Chrome-Moly

These barrels are made from chromium-molybdenum alloy which is harder and stronger than steel, ultimately providing a longer barrel life. They are generally the cheaper option when it comes to AR-15 barrels. When made correctly, some say that they can be close in accuracy to a stainless steel barrel, but not quite in the same league. It will  however require additional care over steel in preventing rust and corrosion.

Stainless Steel

The majority of quality match-grade barrels are made from stainless steel, which is softer and easier to machine than their counterparts. These barrels are more expensive and are often regarded as the most accurate option, best suited for long range precision.

Nitride Barrel

Otherwise known as a Melonite finish, the barrel is immersed in a sodium-nitrogen solution and heated to a high temperature. This converts a thin layer of the barrel’s surface into a very hard coating, making the barrel extremely durable and corrosion resistant. Nitride-treated barrels can withstand direct exposure to water, salt, and corrosive elements better than any other barrel treatment or coating.

Chrome-Lined

The process involves coating the inside of the barrel and chamber with chromium. They are incredibly effective at reducing the effects of rapid-fire and the immense heat it creates. This increases the barrel’s life tremendously. They are also easier to clean and will last longer than a non-coated barrel, but are said to lose around 1/4MOA in accuracy due to the added material within the bore. Chrome lined barrels are often far more expensive than their non-lined counterparts.

So what can we take away from this?

• Well, if your sticking to a budget then the cheaper chrome-moly barrel is perfectly fine, just make sure to look after it and keep it well-oiled during storage or when used out in the elements.
• If long range accuracy is your goal, then a stainless steel barrel might be the best option.
• Should you want serious corrosion resistance both in and out, with good heat resistance and no loss of accuracy, then consider the Nitride barrel.
• If you want an easy clean and intend on firing your rifle at a rapid rate, or you wish to use tracer ammo, then chrome-lining might be the way to go.

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The 5.56mm Fragmentation Range

It is common belief that the 5.56x45mm cartridge is ineffective when it comes to killing and stopping power, which is often a concern when using the cartridge for self-defence purposes. However, by understanding the bullet’s design and how it inflicts damage, you are able to put this myth to rest. So let’s understand it.

• The 5.56mm projectile is light and travels at a very high speed, which makes the bullet prone to yaw in soft tissue.
• If the bullet is travelling fast enough, it is able to yaw and then fragment.
• These fragments can spread and penetrate through flesh and bone, inflicting greater internal injuries and dealing much greater damage to human tissue.
• This fragmentation highly depends on the bullet’s design and velocity, which must be travelling fast enough to cause sufficient yaw and separation of the bullet’s jacket.

Before we discuss the required velocity to typically cause this fragmenting effect, it is important to understand that bullets behave different to one another. Some fail to yaw, or yaw too late in tissue, while others have very consistent yaw behaviour and are capable of inflicting more damage. Research is therefore required in order to find a bullet that meets your needs when it comes to terminal ballistic performance.

Now onto the velocity requirement. In order for the average 5.56mm bullet to yaw and fragment as it was intended to do, the velocity upon impacting its target must exceed 760mps or 2500fps. Breaching this fragmentation threshold causes the bullet’s copper jacket to tear apart and fragment, while the lead core deforms and tumbles. The faster the bullet impacts, the more the bullet will fragment and tumble.

The following table represents the muzzle velocities (approximate) of varying barrel lengths, along with the approximate fragmentation threshold using a 55-grain 5.56mm FMJ bullet. The table also shows the maximum distance at which the bullet will yaw and fragment inside tissue.

Barrel Length	Muzzle Velocity	Max. Distance
24-inches	3330fps	195 meters
22-inches	3265fps	180 meters
20-inches	3245fps	175 meters
18-inches	3190fps	165 meters
16-inches	3130fps	150 meters
14-inches	3015fps	125 meters
12-inches	2900fps	95 meters
10-inches	2740fps	55 meters
8-inches	2460fps	0 meters

It is evident that longer barrels carry an advantage in increasing the range at which the bullet is capable of fragmenting inside of its target. Outside of this fragmentation range, incapacitation relies on shot placement.

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Does the AR-15 Make a Good DMR?

Yes, the AR-15 is capable of making an excellent DMR. For those who aren’t aware, a DMR is a designated marksman rifle; a scoped rifle that is capable of accurately engaging targets at further distances than a standard issue military rifle, which should have semi-automatic capability with a high rate of fire and a detachable box magazine.

In order for an AR-15 to transform into a capable DMR, it should ideally be fitted with an aftermarket trigger, a bipod, a magnified optic, and should be paired with a heavier bullet of match grade.

We did a full article on the DMR rifle, titled: What is a Designated Marksman Rifle.

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Conclusion

After everything that we have discussed above, it’s no wonder the AR-15 is such a popular rifle amongst militaries, gun enthusiasts, sports shooters, and prepper’s worldwide. Oh and not to mention that the rifle is often ranked as one of the top choices for self-defence purposes.

The AR-15 is seen as flawless in the eyes of many, and you’ll either love it or hate it.

Having a good knowledge and understanding of the AR platform will help you to bring out the rifle’s true potential, and with so many uses, the rifle is sure to provide hours of enjoyment.