You’ve decided it’s time to build an AR-15 carbine from scratch. Congrats, that’s awesome! Whether it’s your first build or 15th, seeing your idea come together from scratch is a great feeling. You can make it into just about anything you want. Whether you’re into short-barreled pistols, long-range varmint killers, or an M16 or M4 clone, the world is your oyster.
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But there are a lot of options out there. What length of barrel do you need? What caliber even? And what rate of twist do you need? These are all important questions to ask. Today, we are going to talk about choosing the correct rate of twist for your build.
What Is Rifling Twist?
Most of us are familiar with rifling twist — The distance the bullet travels through the barrel before completing one complete rotation. Shorter rates of twist cause the bullet to spin faster, while a longer rate of twist spins the bullet slower.
Why in the world do you want it to spin faster or slower? In short, different bullet weights require a faster or slower rate of spin to achieve the best results.
The ultimate goal of rifling is to produce consistent strikes on target in the same spot. By this we are referring to the capability of the rifle, not the shooter; with modern firearms which are created in controlled environments, most variations in shot placement have to do with the person shooting the gun, not the gun itself.
But why spin on along a horizontal axis? Pull out your football and do a science experiment.
Try to throw the football around without putting any spin on it. How well does it travel when it wobbles? And how effectively does the football get to your target? Terribly. Bullets are no different. A stable bullet travels faster and farther than a wobbling bullet.
What Are the Most Common Rates of Twist?
For the sake of this article, we’re only referencing .223/5.56×45 barrels. With the AR-15, you can go down too many rabbit holes when you start talking about other calibers.
There are three common rates if twist used in .223 barrels:
- 1:7 – One complete twist every seven inches.
- 1:8 – One complete twist every eight inches.
- 1:9 – One complete twist every nine inches.
Slower rates of twist are used for heavier bullets, while a faster rate of twist is optimal for light bullets.
Example: The 1:7 rate of twist is the standard rate for M4s and their clones that ingest a steady diet of 55-grain JHPs and M193, and 62-grain M855.
The 1:7 is also common, favoring heavy loads. If you plan to shoot heavier bullets exclusively (in excess of 69-grains), a 1:7 rate of twist would be your best bet.
In recent years, the .223 Wylde chamber has picked up steam in the AR community as a great, all-around chambering that fires .223 Remington or 5.56x45mm ammunition well. Barrels chambered in .223 Wylde generally use 1:8 rate of twist and are the best all-around barrel for all weights of bullets, although ideally the bullets would be in the 62- to 77-grain range.
Which Rate of Twist Should I Choose?
This all depends on what you plan on using your build for. Are you building an M4 clone to plink and keep loaded against two-legged predators? An M-4 profile barrel with 1:9 twist is right on the money.
Looking to do shoot a wide range of bullet weights? You won’t go wrong with a barrel in .223 Wylde with 1:8 rate of twist.
Is There One Rate of Twist That Works for a Variety of Bullet Weights?
They short answer is yes. The 1:8 rate of twist is the most popular all-purpose rate of twist on the market. It’s important to remember that there is nothing dangerous about using any of the rates of twist with bullets outside of the optimal range.
The only dangerous situation is if you use the incorrect caliber for the chamber; the 5.56x45mm chambered barrel can shoot either .223 or 5.56 NATO safely, whereas a .223 Remington barrel can only safely shoot .223 ammunition.
However, the .223 Wylde can also safely shoot both calibers without issue. The .223 Wylde is the ultimate in-between. It is an in-between chamber length, so it can safely handle .223 or 5.56 NATO, and they are mostly outfitted with 1:8 twist rifling — once again, in-between.
Why Does Bullet Weight Make a Difference?
Bullet weights matter a lot, but there is an important factor to take into consideration. Heavier bullets are only heavier because of one factor, bullet length. A bullet cannot grow in diameter so the additional mass can only come in the form of a longer bullet.
Shorter rates of twist exist not to stabilize a bullet because of mass, but instead, length. A longer bullet needs to spin up faster to stabilize in flight. But here’s the thing, some modern projectiles are ultra-light, such as copper and zinc. The bullets are longer than a comparable lead bullet, even though they are the same weight as a lighter lead bullet.
These longer, but light, bullets need a faster twist to give them adequate spin. So, you do need to know about the ammunition you’re using and remain aware of any unique demands or requirements.
None of the rates of rifling twist have any bearing on the overall safety of a barrel, only the chambering of the barrel. A .223 Remington chambered barrel can ONLY be used for .223, whereas a barrel chambered in 5.56 NATO is perfectly safe for either. A good rule of thumb is the heavier the bullet, the faster the twist. Planning to shoot 77-grain often? Go with 1:7. Most M4 clones are 1:9 for use with standard 55- and 62-grain FMJ and HP bullets.
The .223 Wylde has gained considerable traction in recent years because it offers a great in-between in terms of chamber length and pressure, along with a standard 1:8 twist, which is the best for a wide range of bullet sizes.
Whatever your shooting needs are, we have barrels and stripped uppers, complete upper receivers, and complete rifles in the most popular AR-15 calibers. Check out our AR-15 parts and start your custom build today!
Have you ever had a problem using a particular weight bullet due to twist rate? Did it cause keyholing or other performance issues? How did you solve the problem? Share your answers in the comment section.