Rifling Techniques

The one question I see on more AR-15 forums is “what is the best barrel”? And the answer to that question is as varied as the types of barrels that exist for the AR-15.

In the last post, we talked about the types of materials used to make AR barrels. In this article, we’ll explore the types of rifling, how they’re created, and what each one means for you.

The material that an AR barrel is made from is only the beginning! Next, you’ll want to look at the rifling process (the “swirl” pattern you see when you look down the barrel).

There are several ways that a barrel gets its rifling. And just like with everything else involving the barrel, each process affects its accuracy…and will work best for various applications.

First, let’s look at cut rifling (Just so you know, we’re starting with the ‘good stuff’). Cut rifling is one of the most accurate ways to get the lands and grooves cut into a barrel.

The manufacturer takes a drill – NOT like a Craftsman – a super-accurate, sharp-as-knives, drill. The barrel blank already has a ‘hole’ cut through it and the drill is inserted. The drill makes specific, accurate, and razor-sharp cuts into the inside of the barrel, creating the lands and grooves (ridges, swirls, and other non-technical terms).

Each pass-through that the tool makes through that barrel only takes off .0001-.0002 of an inch off the metal, so this is truly a labor-intensive process, regardless of whether it’s done by man or machine!

What does this mean to the AR shooter? Plenty.

It means you can go beyond the standard 1:7 twist (we’ll talk about twist rates later). You can go down into FRACTIONAL twists (1:7.7 or 1:7.9, for example) to get HIGHLY ACCURATE barrel.

Note: You’ll still need to be worth a darn to be able to shoot your AR accurately, but the cut rifling DOES make the process easier. 

As you’ll see in this video, Krieger combines several of the processes we’ll cover in this series (Cryogenic, Cut Rifling, etc).

 ***The cut rifling process is shown at 1:51***

But before you think that cut rifling is the way you wanna go, there are still many other rifling processes to cover!

For example, broach rifling! It is HIGHLY unlikely that you’ll find a broach rifled barrel in any AR you purchase. Virtually ALL of the barrels from WWII were rifled this way, but it’s an antiquated technique which has been replaced with even better methods of rifling.

In broach rifling, a tool is made and lined with teeth. Each tooth cuts a little bit more than the tooth in front of it so that, by the time the tool reaches the end of the barrel, it’s been rifled.

The problem is that the tools are expensive to make and are fragile. So it made sense to mention broach rifling here, but not to go into great detail as its highly unlikely that you’ll ever come across a broach rifled AR barrel.

You’re more likely to find a barrel with button rifling!

Button rifling, unlike cut rifling, uses hydraulic machines to PUSH (or “mush”) the metal out of the way. The metal that is pushed to make the grooves is also used to make the lands.

The tool used in button rifling has what looks like one groove cut in it (called the button). As the machine moves through the barrel blank, this button is what directs the metal to make the lands and grooves in the rifle.

As you can imagine, the machines needed to do button rifling are expensive to purchase, expensive to recalibrate for each caliber, and expensive to recalibrate for each twist rate.

In fact, when a manufacturer receives a new batch of steel, they often have to make a new button because of the variances in each batch of steel.

But, even with the pain-in-the-butt process of having to make a new button for the various calibers, twists, etc…the manufacturers can move a serious amount of barrels through the machine (because the button only has to be pushed or pulled once through the barrel to complete the rifling).

Button rifling also has very little labor and time involved, so most manufacturers use this method to rifle their barrels.

Here’s a video showing button rifling in action:

But, lest you think that you’ll have to settle with either high-end cut rifling or mainstream button rifling…FEAR NOT, dear reader. We’ve saved two final rifling methods for you.

Daniel Defense, Ruger, and FN (and by default, the US Military) use a Cold Hammer Forged (CHF) barrel rifling process.

CHF is different than other rifling processes due to the equipment needed. In each of the other methods we’ve just discussed, the barrel blank is placed on a lathe and a tool goes in and out of the blank in order to make the rifling.

Not so with hammer forging!

In the CHF process, the game totally changes. A special CHF machine holds what looks like an inside-out barrel mold – the rifling is actually on the OUTSIDE of the mold. The barrel blank is placed around the outside of the mold and the machine actually presses the rifling INTO the barrel blank from the inside.

Since there’s no drilling, you have less burring, less slag, and potentially a more durable and thus longer-lasting barrel.

And because there’s less movement from a drill or tool, the heat needed to create the rifling is not as highly generated so the manufacturers aren’t as worried about warping.

Finally, there’s polygonal rifling. A polygonal rifled barrel doesn’t have lands and grooves the way a traditional barrel does. It has…corners. Not like what you were made to stand in as a kid. They look more like a little “m”.

But that’s not the only way a polygonal rifled barrel differs from the rest.

Polygon rifling means less fouling. Fouling occurs either by the bullet (or gas blow-by) not making contact with the land or groove. Its space, available to collect copper or lead, as a result of the bullet not fitting as well in the chamber.

With polygon rifled barrels, it’s BELIEVED that the lack of dark streaks left by the gas or bullet are a result of either the bullet making more contact with the lands of the barrel, or even the barrel having a better seal from the bullet as a result of the rifling specifically.

Again, there is NO “best barrel”…but rather, look for the “best barrel” for YOUR purpose. Knowing whether you’ll be plinking, defending, or competing (3 Gun, distance shooting, etc) will go a long way to determining what type of barrel you’ll need.

But wait – there’s more! You can’t just talk about the type of material and the rifling process without discussing heat treatment options…