Selecting the right AR-15 barrel configuration is probably the most difficult choice you’re going to make early on. But it really shouldn’t be. The trouble is that there’s a lot of marketing dollars thrown around to convince you that you need this or that brand or you’re going to lose the match, be uncool, or even wind up dead in the street!
At least that’s what they’ll tell you. But they’re wrong, and I’m going to tell you why.
So first things first, if we’re talking about your very first AR-15, I suggest that your first AR have a lightweight profile with chrome lining. That configuration will serve 90% of shooters well for a long time.
If, however, you’re past your first AR-15 and want to dive into the world of customization, or even building your own, then this article is for you.
This article summarizes just about everything I’ve learned about rifle barrels in general, and specifically AR-15 barrels. I’ve picked these lessons up from years of study, competition, training, and practice.
While I’m happy to offer my recommendations on specific barrels and manufacturers, that isn’t really the purpose of this article. The simple truth is that there are a lot AR-15 barrel manufacturers out there, and I only have direct experience with relatively few.
So when I offer my suggestions, realize that these are the companies that I know, like, and trust– but that doesn’t mean they’re the only game in town.
Really, this article is about helping you understand the main trade offs and quality indicators of a good AR-15 barrel so that you can make that decision for yourself. I’m not here to be yet another internet expert trying to sell you on the “Best AR-15 Barrel” of the moment.
With that said, let’s begin.
AR-15 Barrels: Bottom Line Up Front (BLUF)
I get it, this is a long post.
My objective is to teach you about AR-15 barrels so you can make the best decision for yourself. If you don’t want all of that, then let’s start with my recommendations.
Selecting the right barrel for you is a confusing process when you don’t know your needs.
Most folks shopping around for their first AR-15 have some vague notion of what they want it for. Needs range from home defense to competition, or the collapse of society (AKA the boogaloo), but they don’t really know helps the rifle fit that role.
I want to break this down by purpose.
General Purpose Lightweight Barrels
This class of barrel performs well at most tasks, but it particularly suited to field rifles that get carried more than shot. Unless you have some special purpose in mind, such as competition shooting or making YouTube videos of mag dumps, then this is where you should start.
If you’re sticking to a budget, then the Faxon Gunner Profile is a great option. It’s light, accurate enough, and will take care of you for a long time. I used this particular barrel on my Minuteman KISS Rifle (pictured).
If you have a bit more money to spend, then I suggest Daniel Defense’s Hammer Forged Lightweight or the Bravo Company USA (BCM) Enhanced Lightweight Barrel.
The BCM barrel is button rifled as opposed to hammer forged, and I discuss the difference later on in this article.
General Purpose, Mid-weight Rifle Barrels
These barrels have slightly more mass, which helps them better tolerate aggressive firing schedules without being too much more cumbersome to carry.
In this category, I don’t really think you should look for budget options. If you need it to well at everything, then you’re going to pay a little extra. My favorite barrel in this class is Criterion’s Hybrid Profile.
If you’re a little more budget conscious, check out the Rainier Arms Mountain Series mid-weight contours.
Precision AR-15 Barrels
In this category, you are no longer concerned with weight. These barrels deliver tight groups and consistent performance all day.
That also means you pay for it.
At the “budget” end, I suggest Criterion’s fluted stainless offerings. I put “budget” in quotes because, obviously, it’s still more expensive than the lower end of the market.
If you have even more cash to spend, then check out the Centurion Arms RECCE or Mk12 barrels, which are the same ones used on the military Mk12 rifle. If this is the path you’re going, then you’re probably building out a Recce Rifle or a Designated Marksman rifle. Check out my build guides for those configurations.
The Marksman’s Guide to AR-15 Barrels
With the quick and dirty recommendations out of the way, let’s get to the meat. The rest of this article explains all of the factors you should know when choosing a barrel for your AR-15 build.
The Rifle’s Beating Heart
When you think about it, the modern rifle barrel is not far removed from the muskets and cannons used during the Revolutionary War. There is a charge, combustion chamber, projectile, and length of hollow metal tubing. As the charge burns, expanding high-pressure gasses propel the projectile down the bore.
Upon exit, the bullet begins a ballistic trajectory.
All of the modern advancements in this technology focus on the mechanisms for loading ammunition into the chamber as well as better manufacturing technology.
The aerodynamics of bullets have seen also significant advancement, but that’s not the topic we’re talking about today.
The barrel affects accuracy, reliability, and handling of your weapon more than any other component. It is fair to say it is the most important choice you make when building your AR-15.
When selecting a barrel, you must balance accuracy, weight, handling, compactness, parts longevity, and recoil characteristics. The choices we have to make to affect these traits include:
- Material & lining
- Rifling method & twist
- Chamber dimensions
- Gas system
There is no getting around it. Every choice you make benefiting one trait will negatively affect another.
Put another way: the more specialized you make your rifle for a specific task, the worse it perform at others.
This is why I always suggest your first rifle should be a general purpose “do-all” that serves well at most tasks while not excelling at any specific one.
The reason I suggest a jack of all trades rifle for new shooters is simple.
New shooters don’t have enough skill to leverage special configurations. I’m not being judgmental or negative in any way with this. It’s a matter of practice and expertise.
Here’s some numbers to illustrate what I’m talking about.
The average life of an AR-15 barrel is about 20,000 rounds. Let’s generously assume that the average new shooter goes to the range once a month and fires 100 rounds through their rifle per session. At that pace, it would take about 16 years to wear out that barrel.
And that was being generous. Most novices shoot maybe 100 rounds every six months.
In contrast, the average professional competition shooter expends between 20,000 and 30,000 rounds per year.
I’m not trying to discourage you.
You can still develop a huge amount of skill on 1,200 rounds per year of structured practice. That’s far more than the average gun owner puts in. I’m illustrating how much practice people at the highest levels of shooting put in.
I want you to understand that the ultra-specialized configurations only make a significant difference when in the hands of highly practiced shooters. A master-class level competitor using a bone stock AR-15 will still trounce a novice equipped with a fully custom top-end match rifle.
The internet just doesn’t want you to think this way. Business want you to spend money.
For example, up until 2014, I would have told you that it wasn’t possible to land hits at 1000 yards with a bone stock M16A2, and then I read about Shawn at Loose Rounds doing it. That act blew my mind and started me on the path to taking marksmanship more seriously.
A basic rifle is capable of way more than most “experts” give it credit for.
Remember the Rules
Underpinning everything about the choice you make is the two rules I wrote about in the first time AR-15 buyer’s guide:
- Mission drives gear
- Buy nice or buy twice
Make your decisions on what you need it to do.
Many of us fall into the trap of buying things for the wrong reason and then try to shoehorn them into roles they’re not suited for.
If you are going to buy it, buy something nice enough to last.
AR Barrel Length: The Long and Short of it
The longer the barrel, the more velocity the projectile starts with.
Velocity is important for two reasons:
- It decreases the amount of holdover necessary for a given range (otherwise known as shooting “flatter”)
- It increases the effective range of the bullet
Longer barrels also usually correspond to lower pressures inside of the rifle, which increases the longevity of the bolt, springs, and other components. This comes at a price, though. Longer barrels translate to increased weight and more cumbersome handling.
Shorter barrels, in contrast, are easier to handle but come at the cost of higher operating pressures, increased noise, and accelerated wear on internal parts. The use of a suppressor almost becomes a requirement once you get to 10.5″ barrels. The noise and concussion become unbearable, especially indoors where permanent hearing damage will occur without protection.
This chart comes from a 2012 article at Small Arms Defense Journal about the effects of barrel length. They measured the bore pressure at bullet exit after cutting the barrel down one inch at a time. Note that a 10.5″ barrel has almost twice the pressure of a 20″ barrel.
This difference in pressure affects the noise, concussion, flash, bolt carrier velocity, and long-term durability of the weapon.
When I was in the military, a base armorer once told me that he practically never sees broken bolts from the M16A2s they had on the racks. The M4s with the carbine gas systems, on the other hand, were breaking bolts pretty regularly as they approached round counts around 10,000.
Accuracy and Trajectory
I’m sure you’ve see a lot of folks talk as if longer barrels are more accurate and use that as a reason to justify them.
That is wrong, don’t believe it. Barrel length has little to do with accuracy.
If anything, longer barrels reduce accuracy potential. Imagine a long 2×4 wood board at the hardware store. The longer it is, the more prone it is to “flex” under stress as you hold it from one end. In barrels, we call this “whip.” Long skinny barrels whip more than shorter or fatter barrels.
Since we want to keep higher velocities and lower pressure, which means we need length, we make barrels thicker and heavier to counteract “whip.” However, this is more of a technical curiosity than anything.
The actual effect of the whip is very small and not something you should be concerned with until you are a seasoned match shooter. That gets into realm of barrel harmonics during the shot, which is beyond the scope of this article
So what do they really mean?
When people talk about longer barrels being more “accurate,” what they really mean is that they think it’s easier to make hits at distance. This is a true statement.
A bullet reaches its maximum speed as it exits the barrel. Velocity begins dropping and gravity takes over immediately after that. Increased velocity means that the bullet drops less at for given distance than a bullet that started off slower.
For you, this means that you could land a hit with less holding over the target or adjustment to the sights. There are other factors involved here, such as the aerodynamics of the fired bullet, but that’s another discussion.
I wrote a much more detailed article on the effects of velocity on trajectory, so definitely check that out. As part of that, I put together these two charts.
The first chart compares a 100-yard zero for a 20″, 16″, and 12.5″ barrel. The red dot represents the point of aim. The black dots show expected impact points 25, 50, 200, and 300 yards. Notice how the overall extreme spread of impacts shrinks as the barrel length increases. It’s particularly noticeable with the 300-yard impact.
The second chart shows the same kind of comparison for a 300-yard zero, and I think it shows the effects much more dramatically.
This is “flat shooting.”
The nice thing is that this over/under is fairly predicable using ballistics. So we can leverage this behavior to our advantage. A battlesight zero, sometimes annotated as “BZO,” means picking a zero distances that keeps all of your shots within +/- some distance of the point of aim. Beyond military, we also call this our Point Blank Zero.
That’s not the whole story though.
Landing the hit is one thing, and we can always compensate by choosing a different zero or using holdovers. The other half of this equation is what happens when the bullet impacts the target.
Effective Range of the AR-15
When we talk about the effective range of a bullet, we are talking about the maximum distance the bullet can travel and still have the desired effect on a target. What that desired effect looks like depends on what you’re doing.
The velocity required to punch a hole in a piece of paper or ring a steel plate is one thing. The energy needed to produce threat-stopping wounds is very different and much higher.
Some bullet designs, such as the light 55gr FMJ or 62gr M855, require higher velocities to produce “terminal effect.” I wrote a lot about this in my series on the Small Caliber High Velocity Program that eventually produced the M16 rifle.
Daniel Watters, who I leaned on heavily for the SCHV series, did an outstanding job assembling the history. The short version of the research is that a lighter, faster bullet could be just as effective as a larger bullet up to realistic combat ranges.
What’s a realistic combat range? Historically, it’s about 300 yards. One of the big debates of the late 1950s and early 1960s was about why the Army insisted on 1000-yard capable rifles when most combat happened at far shorter ranges.
Part of the appeal of the AR-15 was that it was much lighter. Not just the rifle, either, but the corresponding ammunition. Combined, the soldier could carry much more ammunition and participate in firefights for a longer period of time.
But I digress.
This chart shows a plot of starting muzzle velocities of an M855 projectile fired from various barrel lengths. The red line represents the minimum velocity for M855 to have good terminal effect.
By starting at a higher velocity, you give yourself more time and distance to have maximum effect.
Mission drives the gear, so how much range do you need? This is all assuming that you are trying to kill something or stop a threat. If you are interested in shooting paper for competition, then it’s a moot point.
Comparing AR-15 Barrel Lengths
Let’s discuss the most common barrel lengths for the AR-15. Each one has its pros and cons. What you choose is ultimately driven by your goals and needs.
20″ Barrels – Old Reliable
I once had a conversation a special operations member who also happened to be a gun nut. Something that stuck out to me was his insistence that we should never sacrifice velocity if we don’t have to. He later started up a very successful company that produced well known AR-15s, barrels, and accessories.
That mantra always stuck with me.
The 5.56 cartridge and original AR-15 were designed as a pair. The 20″ barrel was the heart, and it’s the workhorse or the AR world.
I would even argue that this barrel length is the most optimized for balancing velocity, longevity, and recoil characteristics.
Look at the velocity chart above and how peak velocity occurs at the 20″ length. Everything was optimized for it.
People accustomed to 16″ and 14.5″ barrels are often blown away at just how smooth the 20″ length is to shoot.
20″ barrels provide the most consistent performance across the widest variety of loadings. There are plenty of modern specialized loads “optimized” for use in a 16″ barrel, but the 20″ length will still do things better.
Aside from the benefits of velocity, the long 20″ barrel gives a balance benefit to marksmen. With the extra length and weight, your rifle has a slight forward balance known as “hang.” This helps reduce the “wobble zone” during aiming.
In other words, the rifle and sights stay more still in your hands.
The trade-off, of course, is that a 20″ barrel is longer and heavier than other options. Clearing a house or riding in a vehicle is more difficult. One Security Forces Airman put it to me this way: the 20″ barrel is easier to shoot, but harder to live with.
There are configurations like the M16A5 which help with the maneuverability aspect, but a shorter rifle is always easier in cramped quarters.
16″ Barrels – The Civilian Standard
The 16″ length is the most common AR-15 barrel length sold today.
It doesn’t do anything particularly better than other options, but it has good all-around performance.
The National Firearms Act (NFA) of 1934 limited a rifle’s barrel to a minimum of 16.1″ before more taxes and restrictions come into play. I suspect that we would see a lot more 14.5″ barrels on civilian rifles, the length of the M4 Carbine, if the NFA was not a factor.
16″ AR-15 barrels offer a good compromise between the full 20″ length and the short barreled rifle class.
It’s still capable of hitting any target the 20″ could hit, albeit with a little more holdover, while only losing about 50 meters of effective range compared to the longer rifle. When you think about it, the difference between 150-ish meters and 200-ish meters effective range isn’t a big deal if most of your shooting is inside 100 meters anyway.
Combined with a collapsible stock, the 16″ gun is compact enough to make living the rifle plenty more convenient. If you’re trying to be a bit more of a clone dork, then the 16″ barrel is your ticket for building a RECCE pattern rifle.
14.5″ Barrels – Military Carbine Length
It had a great reputation for compactness and ease of carrying, but the shortcomings of its low velocity and very loud noise signature were a problem. In fact, the XM177 came equipped with a 4″ moderator to mitigate some of the noise, effectively bringing the length up to about 14″.
To be honest, there isn’t much benefit to dropping from a 16″ to 14.5″ barrel.
In fact, it will cause you more pain than it is probably worth due to dealing with NFA paperwork, taxes, and regulation.
Some people circumvent this by using 14.5″ barrels and permanently welding extended flash hiders to the muzzle. This does bring the length back up to the legal 16.1″, but it also makes it difficult to do any future modifications.
If this is your first AR-15, don’t do this to yourself. Give yourself room to experiment without tripping over federal law.
10.5″, 11.5″, 12.5″ – The Short Barreled Rifles
If you want to see a bunch of forum fanboys go at it with one another, ask them the best length for an SBR. The thread will go on for pages and pages while they hash out the tiny differences between 10.5″, 11.5″, and 12.5″ AR-15 barrels.
The truth is that these lengths all do the same thing and they do it well. They all make for very compact and easy handling carbines. They also come with increased pressures, loud noise, and reduced velocity.
Short barreled carbines are certainly fun to play with, but I wouldn’t want to seriously use one without a suppressor, especially indoors. Keep in mind that this class of AR-15 is purpose-built for close quarters fighting at very short ranges.
Sure, they can hit a target at 300 or 400 meters, but I’d rather have something more suited to the job.
18″ AR-15 Barrels – The “Special Purpose” Length
The 18″ barrel length has an interesting story, and it’s well documented by the Small Arms Defense Journal. After the Gulf War, an idea for a light sniper rifle called Special Purpose Rifle was floated by Armalite.
Later, in 1998, the 5th Special Forces Group brought back the idea and started circulating it around SOCOM. The concept finally rose to prominence when the GWOT started ramping up in the early 2000s. The Navy signed on and dubbed it the Mk12 program.
The SOCOM program was originally modeled on the Navy SEAL Recce rifle and its 16″ barrel. But the 5th SFG guys wanted a 20″ barrel for velocity (see above).
Eventually, the Army won, but bureaucratic red tape caused more headaches, as it tends to do.
The Navy was having trouble requisitioning 20″ match barrels because “the system” kept telling them that 20″ barrels were already in the supply chain. The fact that they were standard M16A2 and A4 barrels and did not meet the accuracy requirement for a light sniper rifle didn’t matter.
So the program office changed the specification to 18″ and said that there wasn’t anything in the system. They got their barrel.
Regardless of its origins, the 18″ AR-15 barrel is very popular in the competition world. It offers a very smooth recoil impulse due to its full-length rifle gas system. The length also maintains good velocity for reaching out with a flatter trajectory.
The primary trade-off is a loss in dwell time between the gas port and the muzzle. This can make it a little touchy about ammo selection in cold weather. I’ll talk more about this when I get to gas systems.
Those who carry rifles professionally do an awful lot more living with their weapons than shooting them. You probably aren’t riding around in vehicles all day with your rifle, doing yard work with it slung across your back, or taking it with you to the bathroom. So worrying about living with your weapon probably isn’t a concern.
Mission drives the gear. How are you going use your rifle? I don’t mean fantasy land expectations of the big igloo, either. I argue that the benefits of shootability and effective range outweigh perceived inconveniences about “living with the weapon” for rifles that only ever move from the safe to the range and back.
Also, as a bonus, we civilians can take advantage of configurations the military never fully adopted.
A great one is combining a collapsible stock with a 20″ barreled upper, the so-called M16A5. That reduces some of the pain associated with full sized rifles and still provides all the benefits. This is actually my favorite configuration.
Now that we’ve covered AR-15 barrel length, let’s talk about profiles.
The Skinny (and Fat) on AR-15 Barrel Profiles
The profile of a barrel refers the thickness of metal at different points along its length.
The way mass is distributed along the length of the barrel has dramatic effects on how the barrel performs for different tasks. For example, a thin profile all the way down, the “pencil” profile, makes a very lightweight and easy to carry weapon. In contrast, a thick profile from end to end, the “HBAR” profile, makes a heavy rifle that sustains accuracy over a long string of shots.
Barrel Heat Management
The balance here is how the barrel handles heat versus how easy it is to maneuver.
There’s little practical difference in accuracy between a light barrel and heavy barrel for the first few shots. They both place the round where you aim them. The differences show up at the barrel heats up.
You might remember from your chemistry classes way back in the day that metal expands as it heats up. For rifle barrels, this expansion negatively affects the accuracy of a barrel. So the faster it heats up, the quicker this decrease in accuracy happens.
If you heat any barrel up enough, you’ll eventually destroy the protective linings, rifling, and harm the steel itself. This was the case at the infamous Battle of Wanat. Most of us will never shoot that much.
Skinny barrels heat up faster, so you expect their accuracy to drop off faster. But they also cool down quicker.
Heavy barrels are slower to heat, so they retain their accuracy longer, but also slower to cool down.
There are far more profiles out there than “skinny” and “heavy.” It’s common to have a heavier mass of steel at the rear of the barrel, near the receiver, and then the barrel gradually tapers to a skinny profile near the muzzle.
This produces a well-balanced rifle that dissipates heat well. Criterion uses this in their “Hybrid Profile” barrel I suggested at the start of the article. Ballistic Advantage calls their version the “Hanson Profile.” Faxon, which I also recommended, calls their version the “Gunner Profile.”
There is also the “Government” profile found on the M16A2, M4 carbine, and many civilian rifles. This has a skinny profile near the receiver and a thicker profile towards the muzzle. There is kind of a funny story behind how that profile came about.
The only real benefit of it is that it moves some of the balance forward for shooters who want a bit of “hang” without increasing the overall weight too much.
The compromise between weight and balance comes down to how easy you want the rifle to carry, how quickly you want to bring it to a target, how well it settles in your hands for precision shooting, and how well handles heat.
You can read more about that in my article on weight and balance.
Choosing Your AR-15 Barrel Profile
Light barrels are best suited to guns that get carried a lot and see easy to moderate shooting schedule. This is most people, including military members who live with their rifles.
Heavy barrels are suited to rifles that need to maintain higher levels of accuracy over long strings of shots. This describes match shooters and precision rifles shot from relatively fixed positions.
As the late Hognose of Weapons Man once put it, “You can carry it all day, or you can shoot it all day, but not both.”
Most people are far better served by lighter profiles.
AR-15 Barrel Composition
When selecting your barrel, you have to choose between Chrome Moly or Stainless Steel. Those descriptions are very broad, with many sub-varieties falling under those labels. Some alloys are more useful than others.
But I’ll get to that.
The two different steels have different wear characteristics. It looks something like this: let’s say chrome moly barrels last to ‘X’ number of rounds before accuracy starts gradually declining until the barrel is spent. A stainless barrel might last slightly longer than ‘X,’ but then its accuracy declines much more quickly.
This is generalized, and ignores the quality of the barrel, rate of fire, heat, or pressure of the loads being fired. All of these things dramatically affect the life of a rifle barrel.
Let’s start with chrome moly.
Chrome Moly Barrels
This is the most common type of steel encountered in AR-15 barrels. It’s a broad category that encompasses several different types of metal. If you read my guide to buying your first AR-15, I mentioned two of them: 4140 and 4150. So let’s start there.
4140 and 4150 are two common steel alloys that include Chromium and Molybdenum. These are called “ordnance steels.”
4140 includes about .40% carbon, and 4150 includes about .50% carbon– hence the 4140 and 4150. In real terms, 4150 is a harder alloy and stands up better to temperature extremes, such as fully automatic fire or very cold weather.
The US Government actually has a specification for small arms barrel steel, known as ORD 4150. This specification is MIL-B-11595E, and lists out the chemical composition required to be compliant.
Of note, the third blend in this spec includes Vanadium. This blend is called Chrome Moly Vanadium, or 4150 CMV. You may also see it called 41V45 steel. The vanadium in this alloy helps promote a finer grain structure, wear resistance, and strength.
A manufacturer may claim their barrel is 4150 steel, but that doesn’t mean it’s actually certified under MIL-B-11595E.
Being both 4150 and 11595E certified is more difficult, and thus more expensive.
A manufacturer that’s gone to the trouble of utilizing certified barrel steel will advertise the fact. If they don’t, then you may be getting a barrel made with plain AISI 4150 steel, which has looser tolerances on its chemical composition.
If you shop around enough, you’ll come across retailers selling AR-15 barrels made from “machine gun steel.” FN USA makes these barrels using their blend of steel intended for the M240 and M249 machine guns. It’s a variety of 41V45.
Stainless Steel AR-15 Barrels
When we start talking about stainless steel barrels, everyone assumes we’re talking about precision rifles and match grade barrels. I want to quickly dispell something, though: the barrel’s material has little effect on the accuracy of the weapon.
Stainless barrels are popular for match rifles for one primary reason: they are easier to machine and finish.
The same small shop can machine, rifle, polish, and lap all in one place. Working with stainless steel also reduces the wear and tear on tooling.
Due to a shortened supply chain and skilled craftsmen, the finished product is cleaner and more consistent from barrel to barrel.
It’s primarily the higher quality consistent finish on the inside of the bore that improves accuracy.
Speaking of finishes inside the bore, another factor is protective linings. Since stainless barrels have a much higher amount of chromium in their chemical composition, upwards of 12% compared to about 1% in chrome moly barrels, they do not need any additional coatings or treatments to resist corrosion.
Historically, the application of chrome lining to rifle barrels meant that the bore was uneven and inconsistent. These inconsistencies disturbed the bullet and reduced accuracy. But I’ll get to that.
In general, due to the manufacturing differences, good stainless barrels are about 30% more accurate than the chrome moly equivalents. Of course, this varies from manufacturer to manufacturer.
The trade-off is that stainless barrels do not handle adverse conditions as well. Due to the necessary inclusion of sulfur in the metal, there is a risk of developing sulfide stringers. That’s a fancy way of saying that the barrel could suffer catastrophic failure under fatigue.
The best way to prevent that is to increase the barrel thickness and avoid very cold or very hot temperatures.
Stainless Alloys for Rifle Barrels
410 and 416r are the top two stainless alloys for rifle barrels.
410 is harder and more durable, owing to its lower sulfur content. The trade-off is that without the extra sulfur, the barrel becomes brittle in temperatures below freezing. To compensate for temper embrittlement, the walls of the barrel must be thicker.
416r is an alloy formulated by Crucible Industries specifically for gun barrels. It’s easier to machine and rated to temperatures down to -40 degrees Fahrenheit. This is the most common alloy you’ll come across. It has more sulfur than 410, so there’s a slightly increased probability of sulfide stringers under fatigue.
IMPORTANT: Do not confuse 416r with regular 416, they are not the same. If you see a barrel advertised as 416 stainless, ask if it is actually 416r before you buy it.
Because of the temper embrittlement and sulfide stringer fatigue concerns, it’s a best practice to avoid lightweight profiled stainless barrels.
AR-15 Barrel Protective Linings
This is where the real differences between chrome moly (CM) and stainless barrels become apparent. CM and stainless barrels, machined bare, have about the same level of accuracy.
But you’re rarely going to find a bare CM barrel on the market. CM barrels require extra lining, typically composed of chrome, to resist corrosion.
To improve corrosion resistance and wear characteristics of combat rifles, it’s important to line the bore and chamber of a CM barrel with chrome.
In the 21st century, manufacturers like Criterion have figured out how to get a more even and consistent layer of chrome in the bore.
I have another barrel from Centurion Arms made of FN’s machine gun steel and double-thick chrome lining that shoots about 1 MOA with good ammunition.
The bottom line is that chrome lining does not deserve the negative accuracy reputation it has today- so long as it comes from a quality manufacturer.
Another interesting option that gained rapid popularity is nitriding. I’ve written a much longer article about this nitrided barrels, so this is just a snapshot.
Nitriding has several trade names: Melonite, Tenifer, QPQ, Salt Bath Nitride, and others.
Nitriding is a surface conversion process whereby manufacturers submerge the barrel in a nitrogen-sodium solution and heat to a high temperature.
Usually between 750 and 1200 degrees. Remember this temperature for later.
The end result of the nitriding process is a very hard “case” surrounding the barrel steel. This case is about 60-65 Rockwell, as opposed to 28-32 found on normal barrel steel. It’s very corrosion resistant and has a much lower coefficient of friction compared to bare metal or chrome.
The “killer feature” of nitriding is that the accuracy of the barrel is maintained while the corrosion and wear characteristics improve.
Nothing is free, though. There are two downsides that I know of.
The first is the temperature required to complete the process, which is very close to those used for stress relieving barrels after rifling.
Specifically stainless barrels.
Stress relief is a huge factor in a barrel’s accuracy. It is possible to undo that important work and hurt a barrel’s performance. More on that in a second.
Secondly, the nitride case is much less heat resistant than chrome. It is not an ideal solution for barrels that see very high volumes of sustained rapid fire. The lining will fail and result in faster erosion of the barrel’s steel.
Again, if you would like more detail about the nitriding process, its positives, negatives, and what exactly I mean by high volumes of sustained rapid fire (hint, it’s a lot), then head over to my article specifically about nitriding.
So Which Barrel Material Should You Choose?
99% of shooters are best served by a quality CM/CMV barrel. Either chrome lined or nitrided.
Well-made barrels are more than capable of turning in 1 to 1.5 MOA groupings. That is more accurate than the average shooter is capable of, especially when most users are blasting cheap ammo that isn’t capable of better than 3-5 MOA to begin with.
It doesn’t make sense to spend $500 on a custom stainless match barrel capable of 1/2 MOA, and then shooting mostly cheap bulk ammo that can’t group better than 3 MOA is a waste.
If you absolutely need better than 1 MOA accuracy, and you only plan to feed it quality match ammunition, then go ahead and get a stainless barrel. If you live where it gets below freezing, stick to 416r stainless.
AR-15 Barrel Twist Rate and Rifling
Rifling describes the grooves cut down the length of a barrel’s bore. These grooves “grab” the bullet and impart rotation.
Like a spiraling football, this spinning action increases the accuracy and range of the bullet. We can measure how stable it is by applying a gyroscopic stability factor.
The stability factor is a combination of the spin rate and the shape of the bullet. Before I get into determining twist rates, let’s quickly look at how we create rifling.
AR-15 Barrel Rifling Methods
There are three ways that manufacturers form the rifling of a barrel: cutting, button rifling, and hammer forging.
Each of these has pros and cons. The balance is between how long it takes, the consistency of the end result, and how much stress the steel undergoes during the process.
Cut rifling is the original “old school” way. A machine cuts each groove one at a time over many passes. This produces the least amount of stress on a barrel but requires the most care to get right. Generally, these are the most expensive barrels due to the extra time and care required.
This video shows a machine performing cut rifling.
Button rifling is the military specification. It involves taking an extremely hard “plug” and forcing it through a smooth “blank.” This cutting plug creates the grooves as it passes through the bore. This is a much faster method but produces much more stress on the barrel steel.
Germany developed this method during WWII as a way to accelerate machine gun barrel production. Manufacturers insert a tungsten “negative” mandrel into a smooth “blank.” A large machine hammers the blank around the mandrel until the desired rifling pattern forms. There is a great article from a 2005 edition of Precision Shooting that covers the history and process well.
This is a fast way to mass produce very consistent rifle barrels. It has a side benefit of creating a metal grain compression pattern and a slightly stronger barrel. The downside, of course, is that it puts a very high amount of stress on the barrel steel.
There are only a handful of companies with hammer forging machines in the US. Daniel Defense, Ruger, FN USA, Remington, and IWI all have them. If you are buying a hammer-forged barrel, it probably came from one of these plants.
This video demonstrates what the process looks like. It is from GFM Machine, which produces most of the hammer forging machines in the world. One of the original engineers who designed the process founded the company.
Stress Relieving a Rifle Barrel
Applying high amounts of force on steel results in stress. If you fired the rifle immediately after rifling, accuracy would quickly degrade as the steel heats up.
To help, we need to stress relieve the barrel.
In short, stress relief means heating the barrel up to about 1000 degrees. This helps removes stresses that built up during the rifling process. This also results in a slight softening of the steel, which is expected. Of note, cut rifled barres do not require this process, which means they are slightly harder than other finished barrels.
Notice the temperature used during the stress relief process: 1000 degrees. That is right around the upper range of the nitriding process. Unless the company doing the nitriding is very careful, there is a risk of undoing the important stress relief work. At that point, the barrel will become very inaccurate as it heats.
The rifling process is interesting but is honestly not that important. Worry less about marketing hype. Buy from a quality manufacturer and let them worry about how the barrel gets made.
AR-15 Barrel Twist Rate
A barrel’s twist rate describes how quickly the grooves spiral. Twist rate is denoted as 1/7, 1/8, 1/12, etc. Pronounced “one in seven,” for example, this means that the groove completes one 360-degree rotation around the bore every seven inches. The smaller the number on the right, the faster the twist rate.
You may have heard that you should tie the twist rate to the weight of the bullet you want to shoot. Technically, that is wrong. If you want the long and detailed version, check out my write up on twist rates.
The short version is that the ideal twist rate is a combination of a bullet’s diameter, length, and how weight is distributed. More length, and more mass, for a given diameter needs a faster twist to stabilize it.
The original AR-15 barrels had a 1/14 twist rate. Later, the specification changed to 1/12 for use with M193 55gr bullets. When the M16A2 arrived, the twist rate increased to 1/7 to better work with the long tracer rounds.
For a long time, most civilian AR-15 barrels had a twist rate of 1/9.
The 1/9 twist is actually a really good compromise for shooting most common bulk ammo between 45gr and 62gr. But since the military specification is 1/7, it has been deemed “most desirable” by serious users.
But with the popularity of 77gr SMK for match shooting, 1/7 twists now reign supreme. A 1/8 will shoot just about anything 77gr and below well, but it’s a lesson common twist rate.
I put together this chart to help show you the ideal twist rate for various bullets.
Some people speculate that you can over-stabilize a bullet if you fire it through a barrel with too fast a twist rate. Generally, that is wrong. But, if you fire thin jacketed lightweight bullets or smaller cast lead, you could see some issues.
Ballistician Bryan Litz does point out that there is an optimum twist rate for maximum accuracy. If you reference the chart I put together above for twist rates, bullets do best when the stabilization factor is between 1.5 and 2.0.
If you do enough shopping around you’ll eventually come across a manufacturer touting their various special rifling patterns.
Remington calls theirs 5r, Shilen calls theirs “ratchet rifling,” and there are other names.
Traditional rifling consists of grooves cut down the length of the bore with edges that “grab” the bullet. This pattern is called “land and groove.” Polygonal rifling uses swells and smoother angles to do the same.
There isn’t much difference in performance between them. Don’t let the marketing hype fool you. If anything, polygonal rifling is slightly easier to clean up due to the smoother surfaces, but you aren’t likely to see any real difference in accuracy.
AR-15 Chamber Dimensions
The .223 and 5.56 are very closely related. In fact, most people think they are identical. Dimensionally, they pretty much are.
The difference comes down to the pressures that each generates. 223 is a SAAMI specification, so everyone knows how to follow it for the civilian market or reloaders. On the other hand, 5.56 is a military specification and one that’s changed a lot over the years as velocity requirements have changed.
SAAMI and the US Military measure pressure differently, so there really isn’t a way to directly compare them.
Common wisdom is that firing a 5.56 cartridge in a .223 could result in catastrophic failure due to overpressure. I think those fears are a little overblown, but I understand where they’re coming from.
There are other chambers that split the difference between the two, like .223 Wylde or Noveske’s Match Mod 0.
Due to tighter dimensions, you should expect .223 chambers to be slightly more accurate. But 5.56 chambers work safely with a wider variety of ammunition.
I think most new shooters are just fine starting with a 5.56 chamber.
Now we have reached the last consideration: the gas system.
The AR-15 is a gas powered rifle, meaning that it uses the expanding gasses from a fired cartridge to eject the spent case and load the next round. It uses some of the expanding gasses in the bore by bleeding it from a hole.
This hole, or gas port, is on the top of the barrel under the front sight tower. Gas flows down a tube, where it meets the gas key of the bolt carrier group. It then moves into the bolt carrier, where the pressure pushes against the back of the bolt and the rear of the carrier. This triggers a reward momentum that unlocks the bolt and cycles the rifle.
Manufacturers must manage the amount of gas entering the system. Too much gas and the rifle action becomes too violent. Too little gas and the action will not fully cycle and cause malfunctions. Manufacturers also have to account for the gas port slowly widening over time as the hot gasses erode the steel.
AR-15 Barrel Dwell Time
Dwell time describes the amount of time between when the bullet passes the gas port, allowing gas into the system, and when the bullet exits the bore. As the bullet “uncorks,” the pressure in the system equalizes again.
On average, for government spec configurations, there is about 7″ of barrel between the gas port and the muzzle. This is pretty well optimized for a 20″ rifle, 16″ midlength, or 14.5″ carbine barrel.
Where you see some trouble is the oddball lengths.
For example, 18″ barrels with rifle length gas systems have two inches less “dwell time” compared to their 20″ cousins. That means the gas port must be enlarged in order to let more gas in the system before the bullet uncorks. It’s sorted out now, but 18″ barrels used to have a bad reputation for being undergassed in cold weather because of this.
The same applies the other direction, with 16″ barrels and carbine gas ports. The extra 1.5″ meant the gas port was slightly smaller.
This dwell time issue becomes very important on the very short 10.5, 11.5, and 12.5-inch rifles, as they all use the same 7″ carbine gas system. This gets even more challenging when suppressors are thrown into the mix.
Selecting Your Gas System
Generally, the longer the gas system, the lower the operating pressure. That means a more gentle recoil impulse and longer parts life. For most people, this really shouldn’t be something you are concerned with.
My advice is to simply buy a barrel from a quality manufacturer, and let them sort out the gas system engineering.
There really isn’t a need to back and review all of the points above. I want to leave you with one more piece of advice.
Let’s take a fictional gun company getting their start. I’ll call them Wildcard Arms.
Wildcard Arms contracts with FN USA to produce a run of very high-quality hammer forged barrels. The specs on the bore are very tight, and the accuracy expectation is high. Not every barrel FN makes will meet this specification, so there is a fairly high “reject rate.” This is expected and built into the higher cost that Wildcard Arms has to pay per barrel. But because each barrel is made to a high spec and consistency, Wildcard gets to charge a premium price for the product.
Another company comes along who specializes in bargains. We’ll call them Athena Defense. Athena approaches FN with a much looser specification and negotiates for a lower price point. FN looks at the inventory and sees they have a lot of Wildcard’s rejects on hand, and offers a good deal on them. Athena accepts the shipment, and away they go.
Both companies are now selling barrels from the same factory, on the same machines, but one has a much higher spec product.
I’m not saying that Athena’s barrels are junk, as FN still a reputation to maintain as well. But I am saying that there is a reason for the price difference. It is foolish to discount that just because they came from the same factory.
Buy nice, or buy twice.
Wrapping it Up
I hope you found this guide useful. Buying a barrel is an intimidating process because of the huge number of choices that you need to make. The length, profile, material, lining, and gas system all have an effect on the performance of the gun. But, despite all the text above, the difference from one configuration to the next is not as important as the quality of the manufacturer.
Don’t spend an excessive amount of money chasing accuracy. A quality basic barrel is capable of holding 1 to 1.5 MOA. That is more than accurate enough for even most match shooters, much less a new shooter just getting into things. The mechanical accuracy of the barrel is far less important than the marksmanship skills of the shooter.
Let me know if this article was helpful, and feel free to ask any other questions you might have. Whatever it is, you’re probably not the only one thinking it.