AR-15 Barrel Frequently Asked Questions
AR-15 barrels can be as short as 4 inches for blowback operated AR pistol builds up to as long as 24-inch rifle length barrels.
A 16-inch barrel is the required minimum length for rifles to not be designated as 'Short Barreled Rifles' by the NFA, which require a $200 tax stamp to possess.
An important consideration when it comes to barrel length is dwell time.
Dwell time is the time it takes for a bullet to exit the muzzle of a barrel after the primer has been hit.
As you pull the trigger, gasses start to propel the bullet down the barrel, where it acts sort of like a cork in a very long-necked bottle.
The gasses continue to expand, building the pressure behind the bullet as the space between the fired cartridge and bullet begins to grow within the bore.
The amount of pressure present behind that bullet is what determines the projectile’s velocity as it exits the muzzle of the rifle, being spun by the barrel’s rifling as it goes.
Because of this, bullet loadings perform better or worse depending on the length of the barrel. Too short, and the powder in the cartridge cannot be fully ignited to maximize the load’s velocity before the bullet has exited the barrel. Too long of a barrel, and the cartridge will completely burn its propellant before the bullet has exited the barrel. Take a look at our 5.56 and .223 Ammo here.
So, when considering barrel length, it is very important to make sure you match your barrel with the type of ammunition you intend to shoot, while keeping in mind the performance you are looking to achieve.
The versatility of the AR platform has led to high demand for barrels in many calibers. The caliber being shot from an AR will dictate not only the diameter of the bore, but also the chamber size in the barrel extension.
Certain types of ammunition are very similar to each other, such as the standard 5.56 NATO cartridge and .223 Remington.
AR-15 barrels are available in many calibers, including pistol calibers. Here’s a list of the caliber barrels that we carry here at Primary Arms. Click the kind of barrel you want to view.
There are a few important differences between 5.56 NATO & .223 Remington, but the biggest issue will be pressure.
5.56x45mm NATO is loaded to higher pressures, and 5.56 chambers are slightly longer. If you put a 5.56 cartridge in a .223 Remington chamber, you could create a dangerous pressure spike because of that reduced lead and hotter loading.
You SHOULD NOT use a 5.56x45mm NATO cartridge in a chamber marked for .223 Remington.
However, you CAN use .223 Remington in a 5.56 chamber, so if you’re building a rifle up from scratch, you’ll want a chamber made for 5.56x45mm NATO.
Alternatively, you can choose .223 Wylde - a hybridized chambering that safely accepts both 5.56 and .223 with exceptional performance.
Rifling in a barrel is spiraling grooves cut into the bore that twist at a rate along the length of the barrel. These rates of twist impart a degree of spin on a bullet as it is fired down the bore, stabilizing the bullet and improving accuracy.
Projectile weight primarily determines what twist rate is required to properly stabilize the bullet.
Over- or under-stabilizing a particular bullet will result in a flight path that are undesirable and inaccurate.
Imagine a football flying with a perfect, tight spiral as opposed to wobbling off-axis. Thrown with the same velocity, one ball will be much more accurate and fly further.
Twist rate is read as a ratio, where the first number represents one complete rotation of the bullet and the second number represents the distance the bullet must travel down the barrel, in inches, to achieve one complete rotation.
For example, a common twist rate is 1:8. For these barrels, the bullet achieves one full rotation in 8-inches of barrel length.
The vast majority of AR platform rifles are operated by a direct impingement gas system that cycles the bolt.
The design and the difference in this system will affect the shooting experience of your rifle and even its performance in certain circumstances. Check out ourblog on gas systems to learn how they work in detail.
Fine-tuning the recoil of your rifle is also possible with an adjustable gas block that lets you select the amount of gas entering the system.
It is important to note that too heavy of a buffer weight or improperly adjusted gas blocks can potentially cause the rifle to cycle unreliably as the gas pressure acting on the bolt carrier group will not be able to move the buffer effectively.
Most AR barrels are sold with threaded muzzles to accept muzzle devices, the alternative is a barrel with a target crown, similar to handgun barrels. Check out our AR15 Muzzle Devices here.
On .223 and 5.56 barrels the thread pitch is most usually 1/2 inch x 28 which means that it’s a half-inch diameter with 28 threads-per-inch.
Muzzle devices have many uses which are covered in-depth on themuzzle device buyers guide.
Now that you have learned all there is to know about AR-15 barrels, you should feel confident in your ability to select the right barrel, with the right features to be the best AR-15 barrel for your money and your application.
AR barrels are usually made from 4100-grade Chrome Moly steel alloy, most commonly 4140 -- which can be cheaper -- or 4150 which includes Vanadium in the alloy to increase strength.
The hardness ratings of each type are the same, and while each alloy does include chrome, it is not a large enough amount eliminate rust forever.
416R Stainless Steel is also commonly used in AR barrels and it has more chrome, making it more corrosion resistant. This material is also popular for building a PRS competition rifle.
It can be polished for a distinct look, shot peened for a matte, less vibrant appearance, as well as colored with chemical treatments to feature a dark finish.
Chrome lining in the bore of a barrel was seen as a huge breakthrough for reliability when it was first introduced.
The lining provides a protective coating against corrosion and fouling, which increases the life of the barrel. However, over time, chrome lining can reduce accuracy since the coating unevenly wears down the length of the bore.
Many manufacturers have refined their processes and produce barrels that are highly capable with chrome lining.
More recently, proprietary methods of nitrocarburizing the lining of a barrel have been patented, and these forms of barrel linings will use trademarked names like Melonite, Tenifer, Salt Bath Nitride, and others.
The nitrocarburizing has the outcome of a chemically altered surface inside the bore of the barrel. This lining is becoming more popular, due to its lack of negative effect on accuracy.
For the most supreme accuracy, an unlined stainless-steel barrel will give the best performance. The tradeoff is a lack of protection against corrosion, and shorter barrel life.
Those who are looking for a barrel that will perform at a high level across the widest number of applications, a 4150 Chrome Moly Vanadium barrel with a chrome or nitrocarburized bore lining will fit the bill.
If you’re building a precision rifle that needs ½ MOA accuracy and will never be subjected to sustained high rates of fire, a stainless steel, unlined barrel may be what you’re looking for.
Barrels for AR-15s come in a variety of finishes and coatings and each type presents different performance characteristics to choose from.
Phosphate coating, or 'Parkerizing', is a commonly found process for coating steel barrels. It involves submerging the barrel in a phosphoric acid solution that is heated to around 200 degrees.
Doing so, imparts a phosphate coating to the entire metallic structure. This improves lubricity, corrosion resistance and will have a matte black or grey finish that will not reflect light.
A phosphate finish can provide increased protection for the metal but needs to be kept well-oiled or it will be prone to rust or tarnish.
The process of nitrocarburizing is considered a step above phosphate coating. That's because it's easier to protect against rust and corrosion than phosphate coating. Nitrocarburized barrels can have an even darker appearance than phosphate coated barrels, have a smoother finish, and a more polished look.
There are many styles of Barrel contours, or profiles, and a lot of them can appear similar. It’s also not always clear why certain profiles or contours are designed the way they are.
Sometimes the answer to the latter question is as simple as 'the barrels were bending when soldiers were using them to pry open crates, so we made them thicker on the end.' Seriously.
That’s the reason behind the extra material at the muzzle end of a M16A2 rifle barrel according to Eric Kincel of Bravo Company USA.
When it comes to selecting which barrel profile is right for you, consider the performance demands you’ll be putting on your rifle.
A 'heavy' barrel, sometimes denoted as an HBAR barrel, will lack the various changes in thickness along the length. Most will have two different thickness radii, with one transition point somewhere in between them.
These will be the heaviest to carry, but also will heat the slowest, keeping your accuracy truer for longer.
The vast majority of AR owners will never shoot enough ammunition fast enough to need a heavy barrel in the entire time they own the firearm. Lighter weight barrels with contour types such as government, gunner, tapered, M4, SOCOM, and Pencil, will be perfect. You can find some of our best here.
Some manufacturers will even have proprietary profiles that are engineered to combine some great characteristics of many different contour types. The biggest advantage to these lighter barrels is the decreased weight, which can be crucial if this is a rifle you’ll be carrying for long periods of time.
Common features found on many barrels today are processes used to reduce weight through fluting or dimpling.
These barrels will have long, shallow sections of removed material, or small circular pieces of material removed from the surface of the barrel. As cool as this looks, these are not merely stylistic features.
These processes allow for weight to be reduced on heavier barrels, and increase overall surface area allowing for better cooling.