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AR-15 Barrels Explained (Barrel & Steel Types + Coatings)

The barrel is the most important part of your entire AR-15 build. Your barrel determines how accurate and reliable your rifle or pistol is, it dictates what types of rounds you can fire, and it’ll play an important role in picking out your gas system, handguard, and buffer setup. An entire book can be written on the AR-15 barrel, but we’re going to keep this guide simple by sticking to the important stuff. We’ll explain what types of barrels you can buy, how they’re made, what types of steel all these barrels are made from, and what types of coatings and treatments you should consider.

Let’s get started!

How AR-15 Barrels are Made

There are two primary methods of barrel manufacturing in today’s black rifle market: Cold hammer forging and cut rifling. There are others, of course, but these two comprise a majority of the barrels on the market. 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. This is mostly because they’re bomb-proof, they’re favored by defense personnel and military groups, and they’re accurate. They’re 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. This process requires approximately 50 tons of force per hammer.

This is a cold hammer forging machine. Four rounded hammers pound the barrel blank in quadrants. Note the mandrel inside the blank.

 

Okay, 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 by some degrees. 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 largely unnecessary given the advancements in cold forging tech and stress-relieving processes.

Pros

  • 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

Cons

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

Once the equipment is purchased, cold hammer forging barrels actually becomes more cost-effective for big gun manufacturers. That’s one of the reasons why CHF has become so popular: It produces superior barrels at a lower cost. Win-win.

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.

This P & W Cut Rifling Machine was made in 1895. It was used to produce some of the most accurate rifled barrels of the time, until it was decommissioned in WWII.

 

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. Only instead of being cut externally, this “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.

Pros

  • 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

Cons

  • More expensive to produce than CHF
  • More time-consuming manufacturing process
  • Low-quality barrels are more susceptible to accuracy issues

CHF vs. Cut Rifling: Which is Better?

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

Either barrel will serve you just as well.

Both options will likely provide more accuracy and capability than the average shooter can accomplish.

If you absolutely must pick between a CHF or cut-rifled barrel based on certain unique 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. We want to stress, however, that these subtle differences will only become apparent if you’re purchasing the absolute best of the best in each category.

And even then, these differences will only become apparent to the very rare shooter who’s chasing sub-MOA accuracy at long range and throwing 10,000 or more rounds down the muzzle doing it. If that isn’t you, either barrel will perform just the same.

Types of AR-15 Barrel Steel

The types of steel used to make AR-15 barrels have also been argued and exhausted in forums and threads across the black rifle community. There are loads of misconceptions about what types of steel are even used to make barrels. Let’s clear everything up. There are seven types of gun steel used to make AR-15 barrels, and they can be separated into carbon and stainless steel.

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

“4150 CMV” and Mil-Spec Barrels Explained

4150 CMV is the most popular type of steel you’ll find when shopping for an AR-15, only there’s one problem: The name for this steel is redundant and creates confusion. Allow us to explain.

The phrase “4150 CMV” is a term firearm marketers came up with. Before the AR-15 became wildly popular, most civilian rifles had barrels made from 4140 steel, which is a softer barrel steel that’s easy to manufacture. But military-issued Colt M4s and M16s have barrels made from CMV.

When the AR-15 market rapidly grew, shooters didn’t want 4140 barrels anymore. They started wanting the same barrels the military used. Except someone in the civilian barrel market started saying that all 4150 gun steel was mil-spec. Now, 4150 barrels can be mil-spec, though not always. And real, mil-spec CMV is actually just a variation of mil-spec 4150 steel. It contains slightly less carbon, manganese, and sulfur, and it includes vanadium (the chart below illustrates this).

4150 CMV = 4150 + Vanadium = Mil-spec/CMV

So, to make customers happy, barrel makers started doing two things: One, they started buying 4150 steel and adding Vanadium to it,. Other manufacturers simply started buying CMV steel and making barrels. Except in either case, they were all calling all these units “4150 CMV barrels”. Even though there are slight differences in what elements are contained in each alloy, the name stuck, and the rest is history. Officially, these barrels should be called “4150 Mod V” (which is mil-spec 4150 steel with vanadium added), or simply “CMV”. Industry insiders also call it 41V50, which is the proper designation for this alloy.

So, if you want a real, “mil-spec” AR-15 barrel, you need to purchase a barrel or upper assembly labelled or described as “4150 CMV“, “4150 V“, “41V50” or “MIL B-11595“.

MIL B-11595 Explained

This nomenclature, “MIL B-11595” is another misconception because it isn’t a type of steel at all. In fact, MIL B-11595 is the military’s specification document (click to download the full .PDF) that lists the manufacturing requirements, specifications, and metals and elements contained in mil-spec barrels:

And from this chart, you can see the three types of official mil-spec steel are 4150, 4150 Resulferized (which contains more sulfure), and Chrome-Moly-Vanadium, or CMV. To make things even more confusing, mil-spec 4150 steel won’t always have vanadium included.

Stainless Barrels Explained

Luckily, stainless barrels don’t suffer the same confusion and redundancies. There are three “tiers” of stainless steel barrels: 410, 416, 416R, and 17-4 PH.

Benefits of Stainless vs. Carbon

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.

Disadvantages of Stainless Barrels

Stainless barrels aren’t without an Achilles’ Heel. Below is an excerpt from Michael Moyer, a metallurgist who provided a professional opinion on the disadvantages of 400-series stainless:

“To achieve the high strength the steel must possess to withstand the forces produced during firing, 416 stainless and 4140/4150 barrels must be austenitized, quenched and tempered. After quenching, the average 416 stainless steel will be about 40 Hardness Rockwell C (HRC) while 4000 grades about 50 HRC (to benefit those who do not know this scale, a file will be about 60 HRC, and a hammer will be about 30 HRC). In the “as quenched” state, the steel is brittle and unstable. Tempering is employed to reduce the hardness to a “tough” state and stabilize the newly formed martensitic structure. In the case of 416 SS, and to get the hardness to about HRC 30 so it is able to be machined, one must temper at about 1075 °F.

This is not desirable as 416 SS shows a marked reduction in impact resistance when tempered between 700 °F and 1100 °F (temper embrittlement). It will also show a marked decrease in corrosion resistance. 416 SS does still, however, exhibit better wear characteristics and corrosion resistance than the 4000 series high-strength grades mostly due to the higher chromium content. It is also readily available, inexpensive, and it looks good so manufacturers use it. The big problem though is that it is not as free-machining as the 4000 series grades. So, sulphur is added to alleviate that problem.

What you then have is a micro-structure with “sulphide stringers” in it that has been tempered in a bad tempering range so the impact resistance of the steel is very poor. The 4140/4150 grades do not have this temper embrittlement problem, and show superior impact resistance when tempered to about 30 HRC. They are cheaper to buy in a production rifle. As a note, 410 SS is a better alternative to 416 SS as it does not generally have the sulphur issue, however the temper embrittlement issue is still a concern.

Here is my opinion: Unless you are competition shooter, buy the non-stainless grade barrels. If you are a professional match shooter find a good 17-4PH stainless barrel as it is a much better choice if one wants corrosion resistance, wear resistance, and impact resistance.”

Now, let’s break down the three tiers of stainless barrel steel:

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.

Summary

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 nowadays.
  • Either barrel will perform with better performance than most can handle.
  • If you must pick one or the other, go for 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 stainless.
  • 4150 CMV technically doesn’t exist. It’s just 4150 with Vanadium added, or simply real CMV.
  • If you want a mil-spec barrel, look for one labelled “4150 CMV”, “4150 V”, “41V50” or “MIL B-11595”.

 

Summary
AR-15 Barrels Explained (Barrel & Steel Types + Coatings)
Article Name
AR-15 Barrels Explained (Barrel & Steel Types + Coatings)
Description
This guide breaks down the AR-15 barrel, how it's made, what types of steel are used (and which ones aren't real), and the types of coatings. Learn everything you could ever need to know, including what a mil-spec barrel is really made out of.
Publisher Name
https://www.80-lower.com/
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DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80 Lowers, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

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