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What’s the Deal with AR 15 Twist Rates?

Ah, twisty ole’ twist rates. They’re the bane of so many gun forums, the source of debate, conjecture, expletives and troll-ish comments. Unfortunately for you, the AR 15 builder and shooter, this topic cannot be ignored. Twist rate is one of the biggest variables in the black rifle game when it comes to how you’ll build your rifle (or pistol) and how accurate (or side-of-barn-shot-group inaccurate) it’ll be.

What’s in a Twist Rate?

What is twist rate? Let’s break it down: Twist rate is the number of times your barrel’s rifling’s lands and grooves make one full rotation, measured in inches. For example, our most popular 5.56 upper, our 16” stainless barrel with a 13.5” M-Lok handguard, shows a twist rate of 1:7. That means that every seven inches, the rifling makes one full rotation. Simple math says your round will spin just over two times before exiting the barrel.

The spin imparted on your cartridge stabilizes it and causes it to act consistently and predictably at different distances. It is this stabilizing twist, akin to a good quarterback throwing the ball, that helps you know where your rounds will go every time.

See why it’s so important?

What Twist Rate is Right for Me?

Excellent question. The answer depends on how you plan to build your rifle, what barrel length you want, and what you want to do with your rifle. Amateur builders rare account for the types of rounds they’ll prefer to shoot before building, and it is this rooky mistake that results in poor shot groups and frustrating range days.

The Logic

The logic is simple: The heavier the bullet, the faster the twist rate. Basically, it takes more energy to rotate a heavier bullet and stabilize it. To accomplish this, a more compact rate of twist (often called a “faster” twist rate) converts more of the bullet’s forward momentum and accompanying energy into stabilizing, rotational energy.

What About Barrel Length?

Here’s where a lot of forum arguments transpire, so we’ll try to be as clear and neutral as possible. Before we even get into this discussion, you must understand something: The average AR 15, chambered in .223 or 5.56, is a 200- to 300-yard gun. Can you make shots beyond than these distances? Yes, but if you’re already doing this consistently, you likely have a custom rifle and more knowledge than what we’re teaching here.

Now that that’s cleared up, let’s talk barrel length and twist rate. They are separate topics. Barrel length provides one benefit to the shooter: Velocity. Twist rate provides one benefit to the shooter: Stabilization.

Are there correlations between the two? Yes. Should you decide what twist rate your barrel will be based on barrel length? No. You should choose twist rate, regardless of barrel length, based on the weight and type of round you’ll shoot.

300 Blackout (8.5" Barrel & 7" Keymod Handguard) AR Pistol Upper

Our 8.5″ 300 BLK upper provides plenty of accuracy for supersonic and subsonic loads in a compact build

Shorter barrels favor lighter loads. This is because a shorter barrel provides less velocity build-up, so lighter loads benefit the shooter by achieving their optimal velocity sooner. Most folks who build SBRs or our AR pistol kits – using uppers that are 10.5” down to 7.5” – shoot rounds weighing around 62 grains. That means you’ll want to stick with standard XM193 or M855 cartridges and a 1:8 or 1:7 twist rate. This provides the best balance of weight and stabilization in compact ARs.

Twist Rate and Bullet Weight

Here’s a general rule of thumb when it comes to twist rates in an AR 15 barrel, regardless of length:

  • 40-grain bullets need a 1:12 twist rate.
  • 55-grain bullets favor a 1:9 twist rate.
  • 62-grain bullets favor a 1:8 or 1:7 twist rate.
  • 77-grain bullets favor a 1:7 or 1:8 twist rate.
  • 80-grain and heavier bullets favor a 1:7 twist rate.

5.56 (16" Barrel & 12" M-Lok Handguard) AR 15 Rifle Upper Assembly

Our 16″, 4150 Chromoly-barreled upper provides 1-MOA accuracy with a 1:7 twist rate

Most barrels will come with a 1:7 or 1:8 twist rate, because most common AR 15 ammunition is configured with 62- or 77-grain loads, though 62-grain is a little more common, even still. Factors will change, and you may end up building a rifle designed for one purpose. If that’s the case, now you know what twist rate will work best for you. Otherwise, now you know what the gold standard is, and why. Get building!


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