We’ve discussed ALMOST every aspect to an AR-15 barrel…almost.

We’re down to chambering, barrel lengths, and contours. Three VERY important subjects when it comes to AR-15 barrels!

Today we’ll discuss chambering. And it’s NOT just as simple as “make sure your barrel is chambered for 5.56mm ammo”.

Put simply, the chambering of an AR barrel determines what kind of ammunition you can shoot out of it.

Yes, chambering in 5.56 allows you to fire either 5.56x45mm ammo or .223 ammo. However, there are a LOT of other calibers/chambering that AR-15s are available in!

For example (and yes, there are links to all the calibers listed below for more information on each one…)

And more!

Choosing the right barrel chambering (as always) just depends on what you’re going to be using the firearm for.

Plinking at the range? 5.56 or .223
Competition? .223 Wylde
Reloading? We love 300 Blackout
Long distance/1000 yard shooting? 6.5 Grendel

See what we mean?

Go through each of the links above (and check back for the 2 “coming soon”) to select the correct chambering for your next AR-15 build!

So, we’ve figured out what the barrels are made of, the processes used to rifle and harden them…what’s left?

Barrel twist rates!

In this section, bullet stability is the name of the game! And stability is determined by the rate of twist in the barrel…well, it’s one of the determining factors, anyway.

In layman’s terms, the twist rate is the number of revolutions the rifling makes inside the barrel.

Think of a Slinky (younger folks, look it up). The spiraling of the toy is what it’d look like if you took away the outer metal of the barrel and only left the lands and grooves inside. You can stretch it out so that the spirals appear farther apart, or mash it together and the spirals will compact. The spirals in a Slinky are the revolutions we’re talking about.

The more times the spiral makes a full revolution, the lower the twist rate. For example, a 1:9 (to be read “one in nine”) twist rate means that, for every 9 inches, the rifling makes one complete revolution inside the barrel.

When it all comes down to it, we’re really talking about stabilizing bullets. That is, taking into account the air that the bullet must pass through and figuring out how long the bullet will remain stable.

The numbers of revolutions made inside a barrel determine the stability of the bullet. So, the lower the number, the more (and sometimes faster) the bullet is spinning, the more stable the bullet is.

Now, most AR shooters are familiar with the 1:7 and the 1:9 twist. In fact, most AR barrels can come with twist rates between 1:6 to 1:12.

For example, in our store, the:

–  7.5” 5.56 AR-15 pistol barrels come in a 1:7 twist
– 10.5” 5.56 AR-15 pistol barrels come in a 1:9 twist
– 16” 5.56 AR-15 rifle barrels come in a 1:8 twist

Note: when it comes to talking about barrel twist rates – BARREL LENGTH DOES NOT MATTER. I listed the examples above to show you that IN THIS INSTANCE (talking about twist rates), barrel length doesn’t determine anything.

A manufacturer could have a 2” barrel with a 1:12 twist rate if they wanted.

So why bring barrel lengths into the discussion? Because that’s one of the first things most shoppers look for when they pick up a barrel in our store. And if you are unsure about what you’re looking at, it may lead to confusion.

Speaking of confusion, we could also go into the various rates, which length of bullet is best with which twist rate, etc. But that doesn’t say a lot – especially if you’re a novice when it comes to AR-15 building (or just want to expand your knowledge).

For the beginning AR-15 builder, a table is a great down-and-dirty way to understand twist rates without a degree in astro-physics.


As with everything else in this series, it all boils down to what you’ll do with the gun.

If you’re plinking, a 1:9 twist is fine. In fact, this is the default twist that most AR manufacturers choose for the barrels on their off-the-shelf firearms. Most 55 grain 5.56/.223 ammo will shoot very well in a 1:9 twist barrel.

However, if you have any inkling of doing anything else with your AR (hunting, for example), then go with a mil-spec 1:7 barrel. That way, you can shoot some of the heavier hunting rounds without having to spend the money to purchase another barrel.

Some of the high-end barrels even start with a 1:12 at the base of the barrel (to prevent deformation of the bullet) and “walk” up to as much as a 1:6 twist to get the extra spin on the bullet as it leaves the barrel.

If you’re a precision shooter, or are looking to get into competition shooting, then choosing the right twist rate for your AR barrel comes from knowing what will be the longest bullet you’ll fire.

Take time to consider your reasons behind the barrel purchase (including long term ideals) and you’ll find yourself owning a barrel you can use and enjoy for many, many years to come.

But once you’ve narrowed down the twist rate, material, rifling, hardening, and finishing you want on your barrel – you’ve still got to figure out which chamber will be best for you!

How’s that Barrel Treating You?

Now that we’ve looked at some of the barrel materials and the rifling process, it’s best to know what types of treatment they’ve received, so that you are (again) choosing the barrel that’s best for the application you need.

First, let’s take a history break.

From the introduction of semi- and fully-automatic rifles, one entity has been the leader in discovering the best way to get the most from each and every gun they use. They use the largest amount of ammunition, have the toughest standards on the firearms they receive, and have been instrumental in some of the biggest breakthroughs in barrel technology over the years.

Of course, I’m talking about our Armed Forces.

In the “good old days”, untreated barrels were being “burned through” in less than 1,000 rounds. (Keep that number in mind. There’ll be a test later.)

That meant, specifically with ARs, a soldier or Marine could literally reach the end of the life of his rifle before the conflict had even gotten good and started. The pressure and velocity make the AR platform especially prone to barrel erosion.

A variety of different treatment processes have resulted from the need to extend the life of a barrel – both in the military and civilian world.

Let’s look at a few of these processes:

We’ll start with the 800lb gorilla in the room – Chrome Lining.

For a long time, everyone and their brother wanted a chrome-lined barrel. They’ll pay extra for it. They’ve heard it’ll last almost forever. They’ve heard it’s the best barrel that ever existed.

And they’re only partly correct.

Chrome lining can protect the barrel from heat and pressure. That’s true.

A good chrome lined barrel can still last for 5,000 rounds before you see any degradation. Maybe more.

However, chrome lining can be uneven in barrels, depending on the manufacturer. The barrels can be SLIGHTLY less accurate than a non-lined barrel (you ARE lining the rifling inside the barrel and therefore there is a slight coating over the lands and grooves, dulling them ever-so-slightly.)

Essentially, chrome-lining is one of those leftover processes that “a guy at the range heard from his buddy at work that his dad always told him…” that chrome-lining was the ONLY kind of barrel you’ll want/need.

This is not to take away from chrome-lined barrels. Like I said, they protect against heat and pressure in an AR. It’s not to say that there are zero benefits to using one.

But there are a LOT of other choices when it comes to barrel treatments. And if you don’t know what they mean – or what they mean to your barrel – you could easily overlook the treatment process that will make the barrel you want work better for you.

Now that we’ve gotten chrome-lining outta the way…let’s look at standard heat-treatment.

Standard heat-treatment comes in oil or water bath, depending on steel type. The barrel is heated to 1700 degrees Fahrenheit, and allowed to cool. This allows the barrel to work harden itself.

But the problem comes with potential warpage issues. And warping on ANY barrel is no bueno.

So it’s best to leave standard heat-treatment to the professionals. Even most gunsmiths won’t heat treat their own barrels.

But wait, kids. There are MUCH better rides in the Barrel Treatment Amusement Park!

The Meloniting/ Salt-Bath Nitriding process heats the barrel to 1100 degrees by dipping it into meloniting salts in liquid form.

This process and the lower temperature being used is dramatically reduced from the standard heat treatment process, giving less chance of warping the barrel, less damage to the steel.

Compared to chrome lining, the meloniting process is both a superior process and cheaper.

And talk about corrosion resistance! You could feasibly throw your barrel in ocean, come back a year later, and it will still look the same! (Please note that we did NOT just suggest that you throw your AR barrel in the ocean).

Meloniting also gives the barrel a Rockwell hardness of between 68-72. Read: that’s stinking HARD! It’ll last longer, it’ll be easier to clean, and reduces copper fouling.

You can fire in excess of 15,000-20,000 rounds without seeing degredation in a melonited barrel. (Remember how many round we said a non-treated barrel could shoot earlier? Told you there’d be a test!)

This can double to triple the service life of the barrel. Your grandchildren will shoot out that barrel before you do!

Note: You cannot melonite a chrome-lined barrel. The chrome and melonite salts have a violent (read: explosive) reaction to each other. We’re trying to increase the life of the barrel, not shorten it!

But there’s one more treatment process worth reviewing. One that only the premium barrel manufacturers even know about!

The Gas-Bed Carborization (Black Nitriting) process is virtually the same as meloniting but using gas instead of meloniting salt.

How is the gas-bed process so different than the meloniting process? I’m glad you asked!

Because gas is used for this process instead of liquid, it’s impossible to get anything less than a perfectly even application – inside and out.
The process also gives the barrel a Rockwell hardness of almost 75 (which is not far from diamond-hardness, by the way).

Just like with meloniting, you can fire in excess of 15,000-20,000 rounds without seeing wear. And just like with meloniting, you CANNOT GBC a chrome-lined barrel without an explosion.

So why aren’t more people talking about GBC? Why wouldn’t every single barrel manufacturer on the planet use this process?

Gas-Bed Carborization is a relatively new process in the gun world. It’s been used by other industries (Snap-On in the automotive world, Boeing in the airline industry) for quite some time.

But as with Browning’s industry-altering modifications to firearms, the gas-bed carborization process has been slow to catch on with the gun world.

However, like Browning’s innovative guns, we feel that gas-bed carborization will eventually set the standard for barrels (or bolts, or triggers, etc) in years to come.

Now…there’s one more treatment process to discuss. Another ‘little-known’ method used to harden barrels that only the premium barrel manufacturers are using now – Cryogenic Tempering.

The cryogenic process looks like something straight out of Demolition Man (you younger kids, look it up). And it’s exactly what you think it is…lemme ‘splain:

To the naked eye, barrel steel – regardless of the type – looks perfect when it comes off the manufacturing line. It’s smooth. It looks blemish-free. But it’s not. Not at all.

Under the microscope, it’s a different story.

When you look at a barrel that has been magnified under a scope, you’ll find stresses. Imperfections. Fractures. (It looks like a mountain range!!!)

These imperfections in the barrel, when heated from repeat firing, can cause cracking, premature wearing, and will ultimately contribute to the ending of your barrel. Not in any catastrophic failure, necessarily. Just to you not getting the full use and life of the barrel you’ve chosen.

Enter cryogenic tempering.

The barrels are SLOWLY cooled to temperatures at -300 degrees using liquid nitrogen (in some cases, by 1 degree per minute). The Germans used dry ice during WWII for the same purpose but only achieved -110 degrees. The process actually eliminates these “mountain range” type stresses…thus, doubling or even tripling the life of your barrel!

And if you’re spending $500 on a match-grade barrel to use in competition, the savings alone is significant!

Less warping, almost zero fouling, increased accuracy, increased wear…does it get any better?

Here’s a video example of how 300 Below cryogenically tempers barrels:

Whether you just want to purchase the cheapest barrel…or you want the fanciest with the most renown name – it helps to know what process has been used to harden the barrel!

But alas, it doesn’t stop there. Next, we explore twist rates!

The one question I see on more AR-15 forums is “what is the best barrel”? And the answer to that question is as varied as the types of barrels that exist for the AR-15.

In the last post, we talked about the types of materials used to make AR barrels. In this article, we’ll explore the types of rifling, how they’re created, and what each one means for you.

The material that an AR barrel is made from is only the beginning! Next, you’ll want to look at the rifling process (the “swirl” pattern you see when you look down the barrel).

There are several ways that a barrel gets its rifling. And just like with everything else involving the barrel, each process affects its accuracy…and will work best for various applications.

First, let’s look at cut rifling (Just so you know, we’re starting with the ‘good stuff’). Cut rifling is one of the most accurate ways to get the lands and grooves cut into a barrel.

The manufacturer takes a drill – NOT like a Craftsman – a super-accurate, sharp-as-knives, drill. The barrel blank already has a ‘hole’ cut through it and the drill is inserted. The drill makes specific, accurate, and razor-sharp cuts into the inside of the barrel, creating the lands and grooves (ridges, swirls, and other non-technical terms).

Each pass-through that the tool makes through that barrel only takes off .0001-.0002 of an inch off the metal, so this is truly a labor-intensive process, regardless of whether it’s done by man or machine!

What does this mean to the AR shooter? Plenty.

It means you can go beyond the standard 1:7 twist (we’ll talk about twist rates later). You can go down into FRACTIONAL twists (1:7.7 or 1:7.9, for example) to get HIGHLY ACCURATE barrel.

Note: You’ll still need to be worth a darn to be able to shoot your AR accurately, but the cut rifling DOES make the process easier. 

As you’ll see in this video, Krieger combines several of the processes we’ll cover in this series (Cryogenic, Cut Rifling, etc).

 ***The cut rifling process is shown at 1:51***

But before you think that cut rifling is the way you wanna go, there are still many other rifling processes to cover!

For example, broach rifling! It is HIGHLY unlikely that you’ll find a broach rifled barrel in any AR you purchase. Virtually ALL of the barrels from WWII were rifled this way, but it’s an antiquated technique which has been replaced with even better methods of rifling.

In broach rifling, a tool is made and lined with teeth. Each tooth cuts a little bit more than the tooth in front of it so that, by the time the tool reaches the end of the barrel, it’s been rifled.

The problem is that the tools are expensive to make and are fragile. So it made sense to mention broach rifling here, but not to go into great detail as its highly unlikely that you’ll ever come across a broach rifled AR barrel.

You’re more likely to find a barrel with button rifling!

Button rifling, unlike cut rifling, uses hydraulic machines to PUSH (or “mush”) the metal out of the way. The metal that is pushed to make the grooves is also used to make the lands.

The tool used in button rifling has what looks like one groove cut in it (called the button). As the machine moves through the barrel blank, this button is what directs the metal to make the lands and grooves in the rifle.

As you can imagine, the machines needed to do button rifling are expensive to purchase, expensive to recalibrate for each caliber, and expensive to recalibrate for each twist rate.

In fact, when a manufacturer receives a new batch of steel, they often have to make a new button because of the variances in each batch of steel.

But, even with the pain-in-the-butt process of having to make a new button for the various calibers, twists, etc…the manufacturers can move a serious amount of barrels through the machine (because the button only has to be pushed or pulled once through the barrel to complete the rifling).

Button rifling also has very little labor and time involved, so most manufacturers use this method to rifle their barrels.

Here’s a video showing button rifling in action:

But, lest you think that you’ll have to settle with either high-end cut rifling or mainstream button rifling…FEAR NOT, dear reader. We’ve saved two final rifling methods for you.

Daniel Defense, Ruger, and FN (and by default, the US Military) use a Cold Hammer Forged (CHF) barrel rifling process.

CHF is different than other rifling processes due to the equipment needed. In each of the other methods we’ve just discussed, the barrel blank is placed on a lathe and a tool goes in and out of the blank in order to make the rifling.

Not so with hammer forging!

In the CHF process, the game totally changes. A special CHF machine holds what looks like an inside-out barrel mold – the rifling is actually on the OUTSIDE of the mold. The barrel blank is placed around the outside of the mold and the machine actually presses the rifling INTO the barrel blank from the inside.

Since there’s no drilling, you have less burring, less slag, and potentially a more durable and thus longer-lasting barrel.

And because there’s less movement from a drill or tool, the heat needed to create the rifling is not as highly generated so the manufacturers aren’t as worried about warping.

Finally, there’s polygonal rifling. A polygonal rifled barrel doesn’t have lands and grooves the way a traditional barrel does. It has…corners. Not like what you were made to stand in as a kid. They look more like a little “m”.

But that’s not the only way a polygonal rifled barrel differs from the rest.

Polygon rifling means less fouling. Fouling occurs either by the bullet (or gas blow-by) not making contact with the land or groove. Its space, available to collect copper or lead, as a result of the bullet not fitting as well in the chamber.

With polygon rifled barrels, it’s BELIEVED that the lack of dark streaks left by the gas or bullet are a result of either the bullet making more contact with the lands of the barrel, or even the barrel having a better seal from the bullet as a result of the rifling specifically.

Again, there is NO “best barrel”…but rather, look for the “best barrel” for YOUR purpose. Knowing whether you’ll be plinking, defending, or competing (3 Gun, distance shooting, etc) will go a long way to determining what type of barrel you’ll need.

But wait – there’s more! You can’t just talk about the type of material and the rifling process without discussing heat treatment options…

The one question I see on more AR-15 forums is “what is the best barrel”? And the answer to that question is as varied as the types of barrels that exist for the AR-15.

So I thought it’d be fun to take a look at the various types of barrels and what they’re best used for…

Please note that it is impossible for me to tell you what the “best barrel” is. I can only tell you what the “best barrel” is for what YOU want to use it for.

With that being said, we need to first examine the materials that barrels are made from:

Show Me What You’re Made Of
First, the Chrome-Moly-Vanadium, or CMV. CMV barrels are great for the average shooter, or anyone looking to get their first AR-15. You won’t go wrong with a chrome moly barrel!

And even with this type of barrel steel, you’ve got options!

Most CMV barrels are made from 4140 steel. The general view is that this type of steel is more thermally stable. Essentially, when it gets hot, the molecules have a tendency to stay in one place (but that’s really any 4000-series steel).

The other type of CMV steel is 4150. This is the steel used by our Armed Forces, believing it’s better for full auto. It’s slightly harder, with a higher chromium count and therefore more rust-resistant.

Truthfully, you won’t notice the difference between the two. The US military uses 4150 because their guns are used in combat. They push the barrels to the ragged edge of what they’re made for. But for most shooters, either steel type will work just fine.

Next, let’s look at Stainless Steel.

Stainless barrels have a higher Rockwell hardness (38-42) than a chrome moly barrel (25-30 on average). That makes the barrels harder.
This gives stainless steel barrels a slight edge over chrome moly barrels for accuracy. In fact, any firearm championship of recent note has been won using a stainless steel barrel.

Stainless steel barrels, contrary to popular belief, aren’t sought after SOLELY for their improved accuracy. Rather, the stainless steel allows the barrel to maintain its shape during shooting. Overall, it has a slight edge in accuracy and wear durability.

And in the shooting world, “slight” is relative (usually 5-10%). “Slight” is also important.

There’s a reason why premium gun manufacturers choose stainless barrels over chrome moly.

You’re paying for the edge.
You’re paying for the higher quality.
You’re paying for the 5-10% “slight” improvement.

Because when you start adding “slights” from all over the barrel (slight improvement from the barrel, slight improvement from the BCG, slight improvement from the trigger, etc)…you start to get not-so “slight” improvements that can mean a WORLD of difference to your aim, depending on what reason, application or competition you need the gun for.

Whether you choose chrome moly or stainless steel, this is going to be the base-line for the barrel you want to purchase.

But fear not, weary AR owner. There are still SEVERAL other aspects you’ll need to look at before you pull out your wallet…

Next week, we’ll look at Barrel Rifling – how each method is done and what it means for YOU, the AR shooter.


You may have heard a gunsmith or one of your more experienced gun-friends use the term. You might even have run across it on the internet.

In fact, this post is being written after seeing a forum comment where one “gun guru” declared that AR-15s are “self-headspacing”. (Ok, now you  “gurus” are just making things up!)

The fact is, headspace is just as important to your AR, whether an AR-15 or AR-10, as any other part or piece of the firearm. Mess this up and you’ll have a lovely new “brass shard-inspired” facial tattoo at best. At worst? Well, let’s just make sure you understand headspace…

Let’s start with the way that each cartridge is positioned in the chamber of the firearm. There are four main different types of cartridges: rimless (think .45ACP), rimmed (.30/30WIN), belted magnum (.300 WinMag), and bottle necked rimless (7.92 Mauser or .308 Win).

The rimless cartridges allow the case mouth to rest on the front edge of the chamber.
The rimmed cartridges have the face of the rim resting on the rim recess at the back of the chamber.
Belted magnum cases have the belt rest on the recess – similar to the rimmed cartridges.
Bottle necked rimless cartridges are put in position by the shoulder of the case resting against the shoulder of the chamber.

That means, whenever you drive the bolt home, rack the charging handle, or whatever means your firearm uses to chamber a round, one of the 4 methods mentioned above is used.

If you want to get technical (and who doesn’t?) headspace is the dimension between the bolt face and the datum line on the cartridge shoulder. Here’s a diagram from Wikipedia to help make more sense:

datum line demo

Now, once the cartridge is in position, it’s time for action! When the round is fired, the case will expand in ALL directions – including TOWARDS the bolt face! This is where headspace really comes into play.

When you pull the trigger to fire the round, one of 3 things is going to happen:

If the cartridge has the proper amount of headspace, the case head isn’t stretched excessively during the expansion process. The result: the firearm discharges as it normally would.

Too Much Headspace?
If the cartridge has too much space, the case head will be pushed back towards the bolt face, stretching it enough to give significant weakness to the “web” (the area just in front of the thick portion of the case head).

When this stretching occurs, it weakens the thinner walls of the case (the part containing the POWDER). Starting to see why this would be a bad thing???

Even if the case head doesn’t separate on the first firing, it may do so at any time afterwards, releasing hot gas at 40,000+ PSI.

The result? Damaged stock and magazine at the very least. Possibly even burns to your hand and face.

Even worse – a condition called “slapback” where the bolt has enough room to accelerate rearward and strike the receiver, resulting in a “bolt-in-forehead” reaction (literally)! In some of the older M1903 Springfield rifles, they have strong resistance to push or pull…but little resistance to shock. In a slapback situation where the bolt slaps back, they become brittle and a receiver may shatter like grenade fragments.

Either way: no bueno.

So what happens if there’s too little headspace?
Well, if there isn’t enough room and the case has to be forced (by pressure) into the chamber by the bolt, it can actually wedge the neck tightly around the bullet, delaying the bullet’s release.

And where does the hot gas go? Out of the primer pocket and RIGHT BACK INTO YOUR FACE. Worst case scenario – it can rupture your eyeball.

Again, no bueno.

How Do You Measure Headspace?
Now that you know you neither want too MUCH, nor too LITTLE headspace, how do you know if you’ve got it right?

There are a number of gauges you can purchase that will give you the proper measurements, from a cartridge headspace gauges to chamber headspace gauges.

But if you’re building an AR for nothing more than fun, why spend the money ($30-70) on a gauge you’ll only use once?

Typically, if you have questions (and don’t want to risk a face full of brass shards), it’s best to ask a qualified gunsmith. We’re happy to measure the headspace on any firearm you bring in.

Have additional questions? Want more clarification? We’re always listening and happy to help!

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