Heat Treatment Options
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!