Stainless vs. Carbon: Which Barrel Steel is Better?

Gun barrels are made from just two types of steel: Stainless, and carbon. When it comes to putting rounds on a target, both types of steel provide different benefits and drawbacks.

So, which barrel steel's better? Is one even truly "better," overall? Let's cover it -- but first, we need to learn what both steels are, exactly, and what makes them different from one another.

What is a Stainless Steel Barrel?

There are four relatively common grades of stainless steel used to make gun barrels:

410

410 stainless steel is an incredibly hard alloy that produces sharp rifling and high accuracy. This alloy is more durable than 416 and 416R stainless, offering the longest rifling lifespan of the three. This steel risks developing brittle inclusions or microscopic cracks in extreme cold. Firing rounds through a 410 stainless barrel below freezing temperatures increases the risk of cracking the barrel.

416

416 stainless yields the highest "machinability" of any stainless steel. This stainless can be easily cut like a carbon steel barrel, allowing for sharp rifling and consistent accuracy. Unfortunately, 416 stainless is so "workable" because it contains more sulphur than 410 stainless. This higher inclusion of sulphur reduces the corrosion resistance.

We recommend avoiding regular 416 stainless barrels.

17-4 PH

Precision shooters laud the advantages of 17-4 PH stainless over 416R and 410 stainless. The "PH" in 17-4 stainless stands for precipitation hardening. This involves heating the barrel, then introducing fine, solid additives, like magnesium, aluminum, titanium, and nickel to the steel's structure. This reduces deformations and warping and produces a finely honed, hardened barrel.

17-4 PH contains 17% chromium. This increases hardness and resistance to heat. It also creates a uniform, smooth finish inside the bore. The inclusion of precipitates allows this barrel to withstand extremely high temperatures without deformation. 17-4 barrels suffer less drift with temperature changes. They preserve accuracy as they heat up and cool down. 17-4 PH barrels are hardened to around 36 to 44 RC.

A 17-4 PH barrel is superior in every way to other stainless and carbon barrels. It offers sub-MOA accuracy out to hundreds of meters. These barrels typically cost 3 to 5 times more than a 416R or CMV barrel.

416R

Today, one type of stainless is now the most popular: Crucible 416R Steel. Developed specifically for gun barrels by Crucible Industries, 416R is a stainless alloy that contains the following elements in its chemistry:

• Carbon: 0.12%
• Chromium: 12.5%
• Manganese: 0.4%
• Phosphorus: 0.03%
• Sulfur: 0.13%
• Silicon: 0.4%
• Molybdenum: 0.4%

416R is favored by gun barrel makers not just because of its chemical composition -- which affords high performance in the context of building reliable rifles -- but because of how the steel's forged and heat-treated. The alloy is hardened, tempered, then annealed at specific temperatures to improve its machinability while promoting high hardness -- a critically important combination of attributes when it comes to making the most accurate barrels possible.

Why Stainless is Favored in Gun Barrels

416R provides what is essentially all the best metalurgical attributes a barrel maker could ask for:

Work Hardens When Cut

Stainless steel work hardens when it is manipulated and formed into shape. When making gun barrels, that means the steel gains more surface hardness while the rifling is cut into the bore of the barrel blank. In other words, the very act of creating the barrel promotes greater accuracy and enhances the life of the barrel. 

Cut rifling is, in the opinion of most gunsmiths, the most accurate method of rifling a barrel -- and it's the most effective way to work-harden stainless steel. Win-win when it comes to obtaining a long barrel life and consistent accuracy.

Resistant to High Heat and Scaling

Stainless is particularly effective at withstanding the high heat rapidly generated by rounds igniting in the chamber. It's also resistant to scaling -- the process of the surface of the steel forming an oxide layer when heated excessively. Such scaling would significantly degrade the life of the barrel by creating small pits and fissures in the surface of the steel.

High Corrosion Resistance

Stainless steel excels at withstanding corrosion from other forms of oxidation, and it is particularly effective at withstanding the corrosive effects that would otherwise result from carbon fouling produced by spent gunpowder, and the hot gasses expelled through the bore by live rounds.

Low Porosity

Stainless steel's high chromium content is what gives the alloy a smooth, polished, non-porous surface. This is exactly the type of surface desired in a gun barrel, as it withstands deposits of carbon and copper fouling, and it's incredibly easy to clean.

This low porosity also promotes more consistent muzzle velocities between live rounds, which directly translates into more consistent shot placement and, generally, better accuracy.

What is a Carbon Steel Barrel?

Carbon steel barrels are, like stainless barrel, made from a few alloys: 4140, 4150, and Chromoly Vanadium, often abbreviated "CMV." There is some confusion about the differences between these three carbon steels, so let's clear that up before we cover the benefits of carbon steel barrels.

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 mega-pascals, 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 but least desirable.

4150 Carbon Steel

4150 steel is also 4000-series steel that contains chromium and molybdenum, like 4140. However, the "50" denotes that it contains 0.50% carbon, which is 0.10% more than 4140. The higher carbon content requires additional stress-relieving treatments. This makes 4150 more expensive and harder than 4140. These barrels have a higher tensile strength of 730 mega-pascals, 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 

The label "4150 CMV" is often used to advertise both CMV barrels, and barrels made from 4150 with Vanadium added. The differences between CMV steel and 4150 with Vanadium added is negligible, providing no difference in performance or quality.

What is MIL B-11595?

Some barrels are is even labeled "MIL B-11595." This is not a steel. It's used to identify a proper "CMV" barrel. MIL B-11595 is the military's specification document that lists the elements contained in mil-spec barrels. 

Looking at the spec sheet, you can compare 4150 with Vanadium added, to actual CMV alloy. Both contain generally the same percentages of carbon, manganese, phosphorus, sulfur, silicon, and chromium. CMV might contain 0.05% more molybdenum, though this is again negligible. 

Why Carbon Steel is Favored in Gun Barrels

With all the attributes of an alloy like 416R, you'd think there is no good reason to invest in a carbon steel barrel -- but there are, indeed, plenty of unique advantages to be found, here:

Easier to Machine

Despite its high carbon content and hardness, carbon steel is actually easier to machine into a gun barrel when compared to stainless steel. This higher machinability translates into lower production costs, which makes carbon steel barrels more affordable.

Higher Heat Resistance

Carbon steel barrels excel at heat resistance, making them far better suited for rapid and automatic fire than stainless steel. That's why most tactical and semiautomatic rifles (the AR-15, in particular) and handguns use carbon steel barrels -- it is, in fact, not that difficult to heat a stainless barrel to the point of degradation. That's why stainless steel barrels are mostly found in bolt actions and, when found on semiautomatic actions, are typically reserved for "slow cadence", long-distance cartridges, like 6.5 Grendel or Creedmoor.

Capable of High Accuracy

Thanks to the quality of modern manufacturing, carbon barrels can provide a level of accuracy that's similar to a stainless steel barrel. When it comes to popular rifle rounds like 5.56/.223, 300 Blackout, and .308 Winchester, those cartridges' ballistic limits will typically be reached long before the limits of a carbon barrel's accuracy is truly tested.

So, Which is Better? Carbon or Stainless?

As mentioned earlier, neither stainless nor carbon steel makes for a universally better gun barrel. Both steels outperform one another in different ways, so it's ultimately up to the shooter's needs and goals to determine which barrel steel is best suited for a particular application.

For Maximum Accuracy, Choose Stainless

IF you're counting tenths of an MOA, or if you're chambering a high-performance cartridge that can, ballistically, approach targets at a kilometer or farther -- like most 6mm rounds -- then a stainless barrel is for you.

Stainless is also a great choice if you're chambering a "hot" round with high muzzle velocities (like, say, .224 Valkyrie or 6.5 Grendel), given the longer barrel life afforded by this alloy. Lastly, stainless is a great choice if you prefer a low-maintenance barrel that's easy to clean.

For Cost and Durability, Choose Carbon Steel

Stainless barrels can get very expensive, particularly if you're investing in a one-off manufacture intended for bench use. You can, however, still obtain incredible accuracy out of a carbon steel barrel -- and save plenty of money in the process. 

Carbon steel is also practically a requirement if you're investing in any sort of short-action cartridge chambered in a tactical rifle. That's why most AR-15 uppers -- especially 5.56 and .223 uppers -- stick with 4150 or CMV barrels.