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 hundreds of grades of stainless steel. But today, stainless gun barrels are almost exclusively made from just a single grade of alloy: 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

Stainless steel, and 416R specifically, provides what is essentially all the best 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 just a few select 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 vs. 4150

These two alloys are highly similar. The "41" in either steel's numeric identifier simply notes that both steels belong to the 41xx series of AISI-SAE alloys -- specifically, Chromium-Molybdenum alloys (which is where carbon barrels get the "chromoly" nickname from, but more on that later).

Both alloys vary slightly in their compositions, depending on the manufacturer. But both contain between 0.5% and 0.95% Chromium, and 0.12% to 0.3% Molybdenum. 

The "40" and "50" values in either alloy denote that 4140 contains 0.4% carbon, while 4150 contains 0.5% carbon. The higher carbon content of 4150 makes that alloy a bit harder and more resistant to heat, but more difficult to forge and rifle during the barrel making process.

Chromoly Vanadium

"CMV" steel is chemically similar -- nearly identical, in fact -- to 4150, but with 0.2% to 0.3% Vanadium added to its chemical composition. This is why you'll often see carbon steel barrels advertised as "4150 CMV." The extra Vanadium provides yet more heat resistance, making it a favorable steel for barrels that frequently see automatic or rapid fire.

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 Barrel Steel is Better?

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.