How Rifle Twist Works

Just reading the title, you might think this would be a very short post. Everybody knows that rifle twist works by spinning the bullet so that it is stable as it flies through the air. Naturally, there’s a bit more to it than that.

Anyone that spends any amount of time at the rifle range or hunting lease will inevitably find himself within earshot of two people discussing barrel twist. Twist as discussed here, refers to the rifling in the barrel of modern rifles making a full 360 degree turn in a given length of inches. As an example, a 1 in 7 Twist means the rifling makes one 360 degree turn for every seven inches of barrel. By the same token, 1 in 9 twist means the rifling comes a full 360 degrees in 9 inches. So, the lower the number of inches, the tighter the twist of the rifling.

The amount of twist you need in a given rifle depends primarily on the length of the bullet. Longer bullets require more spin to maintain gyroscopic stability. Think of it like the difference between throwing a baseball and throwing a football: the football requires more axial spin to remain stable in flight than does a baseball. As you might imagine, this is why heavier bullets for a given caliber require a tighter twist. For convenience, most people refer to bullet weight when discussing barrel twist since when discussing any given caliber of ammunition a heavier bullet will almost always be longer than a lighter bullet.

Many firearms are manufactured with a variety of rifling twists available. For the popular AR-15 platform, several different twists are currently produced. Not all ammo shoots well in all twist ratios. A barrel with a 1×7 Twist tends to be too tight for most lighter, more commonly fired ammunition, but is perfect for heavier bullets in the 69-80 grain range. Firing a light weight 55 grain bullet through a tight twist barrel can “overspin” the bullet and result in a loss of accuracy as the rapidly spinning bullet curves through the air, not unlike a curve ball. Overspinning the bullet can even cause some thin jacketed hollow point projectiles to fly apart from the centrifugal forces of the spin.

Standard military issue M16 and M4 rifles, and their AR counterparts, are commonly found with 1 in 7 twist barrels. Originally designed for the military’s use of SS109 (the official NATO name of 5.56mm, or .223), military testing concluded this twist ratio is actually superior for this steel core bullet. 1×9 and 1×10 twist ratios are sort of the “middle of the road” for .223 projectiles, and these are the most common. We suggest our Lake City military XM193 ammunition for this barrel.

On the lighter side of things, a slower 1×12 boasts excellent accuracy on standard and lighter projectiles in the 40-52 grain range. Older M16 rifles were manufactured with the 1×12 Twist ratio. Our item number ARR-115 offers a conversion upper for your AR that takes less than a minute to install, and the barrel has a desirable 1×12 twist ratio. If you are buying a varmint rifle chambered in .223, chances are it will sport a 1×12 Twist Ratio.

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (7)

  1. Most AR-15 rifles intended for the civilian market are actually manufactured with a hybrid “Wylded” chamber that can safely accommodate both cartridges. The only exceptions are match rifles, which are usually .223 caliber and military M16 rifles which are chambered 5.56mm.

  2. Using .223 in any rifle is fine, however, converting over to NATO 5.56 with much higher powder, therefore, higher energy can be very dangerous. Call the manufacturer of your rifle and get the answer of using NATO rounds straight from them. You can never be too safe in choosing your especially when it NATO vs non NATO.

  3. Although many people use .223 and 5.56 interchangalbly, they are not the same. Ammo marked 5.56 is loaded to higher pressures than .223. If you use .556 ammo in a semi-auto stamped .223 you can have too high of pressure in the chamber and cause damage. Most rifles stamped as 5.56 will fire .223 ammo, although it may not have enough pressure to properly cycle the bolt. You’ll just have to play around to see which .223 will work in your 5.56.

  4. You stated that 5.56 is a .223. My rifle manual states that if your barrel is stamped .223 DO NOT use 5.56 ammo. Then it states if it is stamped 5.56 you CAN use .223 ammo.

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