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The Complete AR-15 Barrel Guide

The Complete AR-15 Barrel Guide

Posted by on Apr 8th 2020

This guide covers all the important aspects of an AR-15 barrel from chamber to muzzle. We're covering the various types of manufacturing, the types of gun steel used to make barrels -- including clearing up all the nonsense about "mil-spec steel" -- and we're even going over barrel treatments and coatings, twist rate, barrel length, velocity, and ballistics.

Need help on assembly? Here's how to install the AR-15 barrel and gas system.

How AR-15 Barrels are Made

There are three primary methods of barrel manufacturing in today's black rifle market: Cold hammer forging, cut rifling, and button rifling. Each type has its own pros and cons.

Cold Hammer Forged (CHF)

Cold hammer forged barrels are some of the most popular on the market because they're incredibly strong, they're favored by defense personnel and military groups, and they're accurate. CHF barrels are made by taking an over-sized barrel blank (a raw piece of gun steel roughly resembling a barrel) and forcing a shaped tungsten-carbide mandrel through the rough, un-rifled bore. The mandrel has the shape of the rifling imprinted on it. With the mandrel inserted, the barrel blank is literally pounded into its final shape by very large hammers, shown below. This process requires approximately 50 tons of force per hammer.

It's not really cold

Cold hammer forging isn't done at "frigid" temperatures, but rather at room temperature. The immense pressure of the forging process does heat up the steel. The finished barrel must be stress-relieved by further heating (baking at a few hundred degrees for 1 to 2 hours) after forging. Hammer forging can also be done hot, at temperatures around 80% of the steel's melting point. Hot forging is unnecessary given the advancements in cold forging tech and stress-relieving processes.


  • Produces an incredibly dense, strong barrel
  • CHF barrels typically have longest rifling lifespan
  • Creates a uniform grain structure that follows the rifling
  • Provides consistent rifling lands and grooves that are highly accurate
  • Creates incredibly smooth, uniform rifling free of small imperfections
  • CHF barrels are favored by militaries and largely produced by defense contractors


  • Production equipment is expensive for manufacturers
  • Extremely high-end button- and cut-rifled barrels have potential to be more accurate

Cut-Rifled Barrels

Cut-rifled barrels are considered the widespread "gold standard" for the AR-15, even today. While cold hammer forging has made mass barrel production less expensive without sacrificing quality, cut rifling is still favored by many manufacturers and it's still the method of production the U.S. Military employs. In fact, this process has been around for nearly 500 years.

A cut-rifled barrel is produced as the name implies: A forged barrel blank with a rough bore is inserted in a large rifling machine, which resembles a CNC lathe. The "lathe" pushes a single cutter attached to a long rod through the rough bore, carving out each land and groove of the rifling. Only a few thousands of an inch of steel are removed with each cutting pass. This process is time-consuming but with the right equipment and technique, a cut-rifled barrel is the most accurate barrel you'll find.


  • Cut rifling produces incredibly accurate barrels
  • Manufacturing process is honed to perfection
  • Top-tier, match-grade barrels are all cut-rifled
  • Creates incredibly consistent rifling profile


  • More expensive to produce than CHF
  • More time-consuming manufacturing process

Button-Rifled Barrels

Button rifling uses a hardened tungsten-carbide "button" attached to a long rod that is forced through the barrel's bore under immense pressure to form the rifling inside. Some makers pull the button through the barrel, while others use a large pneumatic rod to push it through. Because of advancements in cut rifling and cold hammer forging, button-rifled barrels have largely fallen out of favor, especially for the AR-15 market. Virtually all black rifle barrels are cold hammer forged or produced with cut rifling.


  • Relatively fast and economical
  • Well-suited for mass production
  • Produces relatively consistent rifling


  • Button rifled barrels require stress-relieving treatments
  • Rifling buttons are expensive make and maintain

CHF vs. Button vs. Cut Rifling: Which is Better?

You've probably been browsing forums, thread after thread, reading all sorts of opinions about CHF vs. cut and button rifling. The brutally honest answer to your question is simple.

Either a CHF or cut-rifled barrel will serve you just as well as the other.

Both options will provide more accuracy and capability than the average shooter knows what to do with. If you absolutely  must pick between one of the three barrel types based on certain advertised advantages, it boils down to this: If you want a barrel that'll afford the longest possible lifespan, stick with a CHF barrel. If you want a barrel that's as accurate as possible, stick with a cut-rifled barrel. Button-rifled barrels provide no distinct advantage. We want to stress, however, that th subtle differences between CHF and cut-rifled barrels will only become apparent if you're purchasing the absolute best of the best in each category.

Even then, these differences will only become apparent to the very rare shooter who's chasing sub-MOA accuracy at long range with match ammo, and throwing 5,000 or more rounds down the muzzle. If that isn't you, either barrel will perform just the same.

Types of AR-15 Barrel Steel

 There are seven types of steel used to make AR-15 barrels, separated into carbon and stainless steel categories:

  • Types of Carbon Barrels: 4140, 4150, and Chrome-Moly-Vanadium (CMV), also called 41V50.
  • Types of Stainless Barrels: 410, 416, 416R, and 17-4 PH.

Types of Carbon Barrels Explained

There is a misnomer in the AR barrel market concerning the types of "mil-spec" steels available, but we'll explain as we go along.

4140 Carbon Steel

4140 steel is a type of 4000-series carbon steel that contains 0.80% to 1.10% chromium and 0.15% to 0.25% molybdenum. These two elements make the steel much stronger and harder than regular carbon steel. The "41" in the number identifies these two elements. The "40" refers to the 0.40% carbon also added to the steel to make it even harder. This steel maintains a tensile strength of 655 megapascals, or 95,000 PSI. For reference, 5.56 cartridges are proofed 125% maximum pressure, or 77,958 PSI. This type of steel is the most affordable.

4150 Carbon Steel

4150 steel is also 4000-series steel that contains chromium and molybdenum like 4140 steel. However, the "50" denotes that it contains 0.50% carbon, which is 0.10% more than 4140 steel. The higher carbon content requires additional stress-relieving treatments. This makes 4150 more expensive and harder than 4140. It also produces a higher tensile strength of 730 megapascals, or 105,880 PSI.

Chrome-Moly Vanadium (CMV)

Chrome-Moly Vanadium, or simply "CMV", is the official mil-spec gun steel developed by Colt Firearms for the military-issued M16 and M4. It contains the same elements as 4150 steel. It also contains Vanadium. Vanadium significantly increases the strength, hardness, and high-temperature stability of the steel. This makes CMV the most suitable steel for producing machinegun barrels for full-auto or rapid fire.

"4150 CMV" Steel 

4150 CMV is the most popular type of steel you'll see advertised when shopping for an AR-15 barrel or upper assembly. The problem is, this label is a misnomer. The phrase "4150 CMV" is a term barrel makers came up with decades ago that sticks around to this day. 

Story time:

Before the AR-15 became popular, most civilian barrels were made from 4140 steel because it was more affordable. But military-issued Colt rifles had (and still have) barrels made from CMV. When the civilian market grew, shooters didn't want 4140 barrels anymore. They wanted the barrels the military used. Unfortunately, someone in the civilian market started producing barrels made from 4150 and called them "mil-spec" for the AR-15. Although many AR-15 barrels are made from 4150 to this day, this steel was only ever mil-spec for the M14 and M1 Garand.

This misnomer caught on, leaving barrel makers with a problem: Should they produce 4150 barrels because that's what civilian AR-15 buyers thought they wanted? Or should they produce CMV barrels because that's what civilian buyers actually wanted? The solution was to buy CMV steel and make barrels to M16/M4 military specifications, and simply label them "4150 CMV". If manufacturers couldn't get CMV steel, they would buy 4150 steel with the same elements and properties as CMV and add Vanadium to it. 

Either way, per MIL B-11595, "4150 CMV" = 4150 Steel + Vanadium = Mil-spec CMV.

What is MIL B-11595?

Advertising "MIL B-11595" as a barrel steel creates yet another misconception because it isn't a type of steel at all. MIL B-11595 is the military's specification document that lists the metals and elements contained in all mil-spec barrels. Looking at the spec sheet below you can compare 4150 to CMV: Both contain generally the same percentages of carbon, manganese, phosphorus, sulfur, silicon, and chromium. CMV might contain 0.05% more molybdenum, though this is negligible. 

Types of Stainless Barrels Explained

Stainless barrels don't suffer the same confusion as carbon steel AR barrels. There are four "tiers" of stainless steel barrels: 410, 416, 416R, and 17-4 PH.

Advantages of Stainless vs. Carbon Steel

There are two major advantages to picking a stainless barrel over a carbon steel barrel: First, it'll provide better corrosion resistance with better accuracy. A carbon-steel barrel could last longer if it has a chrome-lined finish, but chrome-lining affects rifling and shot placement. Second, a stainless barrel will provide better "toughness". Stainless barrels are more resistant to heat and abrasion than carbon steel. All other factors being perfectly equal, a stainless barrel will last longer than a carbon steel barrel.

410 Stainless

Barrels made from 410 stainless steel include the element molybdenum. The inclusion of molybdenum is meant to reduce the risk of developing sulphide stringers. This stainless steel is actually more durable than 416 and 416R stainless, offering the longest barrel life of the three. The only drawback to 410 stainless is its ability to withstand cold temperatures. Firing rounds through a 410 stainless barrel while below freezing temperatures (32 degrees F) increases the risk of cracking the barrel or causing a catastrophic failure due to sulphide stringers in the metal.

416 Stainless

416 stainless boasts the highest machinability of any stainless steel. This stainless can be easily cut like a carbon steel barrel, allowing for better rifling and more consistent performance. Unfortunately, 416 stainless is so "workable" because it contains more sulphur than 410 stainless. This higher inclusion of sulphur greatly reduces the corrosion resistance, weldability, and formability when compared to 410 stainless.

We recommend avoiding purchasing a typical 416 stainless barrel.

416R Stainless

416R stainless is a newer, proprietary stainless alloy produced by Crucible Industries, an industrial metal supply company. 416R boasts high machinability (and thus accuracy) like regular 416 stainless, except it also includes molybdenum (like 410 stainless). It also contains less sulphur than 416, reducing the risk of catastrophic failure from the inclusion of sulphide stringers. Crucible confirms an AR-15 barrel made from 416R stainless can be safely fired at temperatures as low as -40 degrees (F).

17-4 PH Stainless

Many precision shooters laud the advantages of 17-4 PH stainless over the more typical 416R and 410 stainless options. The "PH" in 17-4 stainless stands for precipitatino hardening. This process involves using heat to make the alloy stronger by hardening it and introducing precipitates (fine, solid impurities like magnesium, aluminum, titanium, and nickel) to the steel. This process also reduces deformations and warping, producing an incredibly honed barrel.

17-4 PH also contains 17% chromium, lending a natural hardness, resistance to heat, and smoothness to the rifling and bore. 17-4 PH barrels do not suffer the same cold-weather concerns as 400-series barrels. On the opposite extreme, the inclusion of precipitates also allows the barrel to withstand extremely high temperatures without deformation, meaning shooters can stay on the trigger and put more shots down-range without the barrel expanding and loosing accuracy. 17-4 PH barrels are usually hardened to around 36 to 44 RC. 416R barrels only harden to 28 RC.

The only downside to 17-4 PH barrels are their ability to withstand sustained, rapid fire. Once the metal is heated nearly to its tempering point through sustained fire, it becomes permanently soft and the barrel is no longer capable of performing accurately (or safely). But getting 17-4 PH to such temperatures is difficult and would take hundreds (if not thousands) of rounds. A 17-4 PH barrel is superior in every way, offering sub-MOA accuracy out to hundreds of meters. They typically cost 3 to 5 times more than a 416R barrel.

Barrel Treatments & Coatings

The method of production and the type of steel used to make an AR-15 barrel are just parts of the total equation. Picking the right finishing treatment and/or coating is just as important, lest you suffer a short barrel life and poor accuracy.

Chrome Lining (Interior)

Ah, the classic and the most widely-marketed type of barrel treatment: Chrome lining. This age-old process involves coating the inside of the barrel and chamber with chromium. Chrome lining adds to the physical dimensions of the barrel itself, so the rifling and barrel must be over-sized if this process is to be performed. Once applied, chrome lining is visible as a silvery finish and it measures a few thousands of an inch. It insulates the rifling and barrel, and it's incredibly effective at reducing the effects of rapid-fire and the immense heat it creates.

A properly chrome-lined barrel is easier to clean and it will last longer than a non-coated barrel, usually by a few thousand rounds. With a quality lining, the loss in accuracy usually amounts to just 0.25 MOA, or around 0.25" at 100 meters.

Manganese Phosphate/Parkerized (Exterior)

Chrome lining only protects the inside the barrel, so most lined barrels also get an exterior manganese phosphate treatment, often branded as a Parkerized finish (named after the Parker Rust-Proof Phosphating Company). A chrome-lined-and-phosphate-coated treatment is the most common type of treatment applied to mil-spec barrels and most current, military-issued rifles. A phosphate finish is incredibly resistant to heat and the elements, but it is also slightly porous. It requires occasional oiling to effectively prevent corrosion.

Nitride/Melonite Finish (Interior & Exterior)

Shooters who want the latest hotness should stick with a nitride finish instead. Also called a Melonite finish (which is a brand that performs this type of treatment), the nitride finish effectively coats both the exterior and interior of the barrel. Unlike chromium and manganese phosphate, nitride doesn't "coat" the barrel. Instead, it penetrates the steel structure itself, attaching nitrogen atoms to the atoms in the steel.

This process doesn't add any physical material to the rifling, so the barrel in question doesn't need to be specially fabricated to accommodate this treatment. Nitride is applied by quenching, polishing, and then quenching the barrel a final time in a liquid salt bath. The nitrogen thus penetrates the steel by a few thousands of an inch. A nitride treatment is technically more effective than a chrome-lined finish.

In fact, nitride-treated barrels can withstand direct exposure to water, heat, salt, and corrosive elements better than any other barrel treatment or coating. Nitride is also non-porous and doesn't require any oiling or extra coating to prevent corrosion. A barrel treated with nitride boasts a surface hardness of around 60 HRC, making it the same hardness as hardened tool steel.

Twist Rates and Barrel Length

Twist rate is the measurement of how much the lands and grooves of your barrel's rifling rotate. This determines the kinds of bullets you'll shoot. It's so important for accuracy that it's advertised in the titles of just about every AR-15 upper and build kit. Why? Twisted rifling gives spin and stability to a bullet as it travels downrange, like a Hail Mary thrown by a quarterback into the end zone. All rifles and handguns must have a twist rate expressed in their specifications. Smoothbore guns (most shotguns, save for rifled slug guns) have no rifling.

How Rates Are Measured

The rate is measured in inches per full rotation and is expressed as a ratio, written as 1:9, 1/9, or 1-in-9. This measures how many inches the rifling travels down the barrel before it completes one 360-degree rotation. For this example, that's one rotation every nine inches. The smaller the number, the more frequent the rifling twists.

Twist vs. Bullet Weight

Twist rate determines how heavy or light your bullets will be, which is usually advertised as a "grain" count or grain weight. The heavier the bullet (higher the grain count), the faster the twist rate must be to effectively spin up and stabilize that round before it leaves the barrel.

Twist vs. Barrel Length

Twist rate is not related to barrel length, and barrel length doesn't affect which twist rate is best for a weapon or cartridge. If the cartridge in question performs best with a 1:10 twist rate, that rule always applies, whether it's fired from a 7.5" barrel, 16" barrel, or a 24" barrel. Barrel length only affects velocity, not the spin of the bullet.

Twist Rate Charts Explained

(Ballistic data courtesy of Everyday Marksman)

This chart provides a visual for which twist rates are best for most 5.56/.223 loads. The numbers in each cell measure gyroscopic stability. Faster rates produce higher factors. Factors between 1.5 and 2.0 are ideal for all bullets and calibers. Factors between 1.0 and 1.3 are marginally stable. Factors between 2.1 and 2.9 are considered fast, but still stable and highly accurate. Factors above 3.0 are suitable, but climbing above 4.0 may begin to cause over-stabilization, or too much spin. Based on this chart, the optimal twist rates for 5.56 and .223 bullets are:

  • 45-gr Varminter: 1:12 twist
  • 55-gr (M193): 1:12/1:9 twist
  • 62-gr (M855): 1:8 twist
  • 77-gr (Mk262): 1:8 twist
  • 80-gr Sierra Match: 1:7 twist
  • 90-gr Sierra Match: 1:7 twist

Overall, the 1:8 twist rate is best for AR owners who want to shoot all common .22 loads. The fast 1:7 rate's designed for match loads, while the 1:9 twist is optimized for the most commonly available ammo ( M855 and M193) at most sporting goods stores and general stores, like Walmart.

What does too much spin do?

A bullet in flight travels with six degrees of freedom: Forward, up and down, and left and right with yaw, roll, and pitch in motion, too.

  • Roll affects the spin of the bullet perpendicular to its travel, like a thrown football.
  • Yaw affects the horizontal rotation of the bullet, like a car turning left or right.
  • Pitch affects the rise and fall of the bullet, like a plane taking off or landing.

The right amount of spin helps a bullet to resist changes to its yaw and roll, and it helps to stabilize its pitch as it arcs from the barrel to the target. Over-stabilization causes spin drift, which makes the bullet yaw in the direction its spinning. Too much drift will cause a bullet to yaw left or right and ultimately tumble, losing its "football"-esque roll and stable flightpath.

Bullet Spin vs. Ballistic Coefficient

Gyroscopic stability correlates directly with a bullet's ballistic coefficient (BC). BC measures a bullet's ability to power through air and wind without changing course. The higher the coefficient, the more accuracy is maintained at longer shooting distances. Generally, a round loses 3% of its BC for every 0.1 loss in gyroscopic stability below factors of 1.5.

Twist Rate FAQs

Q: Are marginally stable twist rates OK?

A: Yes. Even if you invest in a barrel with a twist rate that yields a gyroscopic stability factor of about 0.8 to 1.4, you can still likely shoot with accuracy. As distance increases, however, stability could falter. You may witness one or two keyhole rounds impacting your target as you approach max effective range of the round you're shooting. This indicates bullet spin and stability was lost in flight.

Q: What's a "keyhole" round?

A: A keyhole round is a bullet that impacted its target after it lost spin and stable flight, and began tumbling through the air. The "keyhole" moniker comes from the shape the round makes when it hits the target, resembling that of the keyhole in an old door's lock.

Q: What are the best rates for the AR's calibers, again?

A: Ideal rates for common loads are pulled from our charts above.

  • 5.56 NATO, .223 Remington: 1:8 twist
  • Supersonic 300 Blackout: 1:12 twist
  • 308 Winchester, 7.62x51: 1:10 twist
  • Subsonic 300 Blackout: 1:8 twist
  • 9mm Parabellum: 1:10 twist
  • 6.5 Creedmoor: 1:8 twist

Q: How do I calculate the ideal twist rate for any bullet?

A: The calculation is called the Miller Formula. The formula requires that you know the following data:

  • M: Bullet mass in grains
  • S: Gyroscopic stability factor (1.5 is optimal)
  • D: Bullet diameter in inches
  • L = Length in caliber (bullet length / bullet width)
  • The equation is written as Twist Rate = Square Root of (30M / ((S * D * L (1 + L^2)).


Like we said, you could write a book on the AR-15 barrel. Here's a quick summary of the important stuff:

  • Ar-15 barrels are mostly made by cold hammer forging and cut rifling.
  • Either barrel will perform with better performance than most can manage.
  • If you must pick one or the other, go with CHF for lifespan. Pick cut rifling for accuracy.
  • Barrels are made from seven types of steel: 4140, 4150, CMV, and 410, 416, 416R, and 17-4 PH.
  • 4150 CMV technically doesn't exist. It's just mils-spec 4150 with Vanadium added, or mil-spec CMV.
  • If you want a mil-spec barrel, look for one labelled "4150 CMV", "4150 V", "41V50" or "MIL B-11595".
  • Nitride coatings provide the best performance, while chrome-lining and phosphate work well for rapid fire.
  • For the typical 16" barrel, a 1:7 to 1:9 twist rate is best. A 1:7 twist rate is for match-grade, heavy loads.

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