What is barrel twist and why does it matter?

If you’re anything like me, buying a new rifle can be quite a chore. With popular calibers, there can be what seems like an infinite number of options available. Looking through all these options can get tiring, so some features may be overlooked.

Perhaps one of the most overlooked features when buying a new rifle is the twist rate of the barrel. At a fundamental level, twist rate is not as complicated as you may think, although it does play a vital role in the specific bullets that you are able to shoot out of your rifle.

What is Twist Rate?

Twist rate (in terms of firearm barrels) is known as the distance it takes a projectile to make one full rotation. This rotation is created by grooves that are cut into the barrel at a specific twist ratio.

If you’ve ever looked at the specs of a rifle, you may have seen numbers like 1-8 or 1-10. Whether you knew it or not, what you noticed was twist rate, but what exactly do these numbers stand for? These number sequences represent the twist rate of the barrel, or the distance it takes to make one full rotation. The first value represents the number of rotations, the dash can be substituted with “in”, and the last value represents the distance for the number of rotations.

If we look at a 1-8 twist rate as an example, we see that there is 1 full rotation in 8 inches of distance. The smaller the last number is, the faster the bullet is spinning. A barrel that has a twist rate of 1-8 is spinning a projectile at a much faster rate than a barrel with a 1-14 twist rate.

Depending on bore size and bullet type, twist rates generally range from 1-6 for heavy bullets fired out of small-bore sizes (22 caliber, 6mm, etc.) all the way up to 1-36 for slug guns. There are however, some exceptions to this range such as the new 8.6 Blackout which has a 1-3 twist rate.

Why is it important?

Now that we have discussed exactly what twist rate is, let’s go over why it is important. For a bullet to fly accurately down range, especially at extended ranges, stabilization is key. Outside of the design, there is only one factor that will create stabilization in a bullet. That factor is spin.

Much like a football needs to be thrown with a certain amount of spin for it to fly accurately down field, a bullet needs a certain amount of spin to fly accurately down range. Unlike a traditional football however, bullets come in all different shapes and sizes.

The shorter and wider a bullet is, the less spin (twist rate) it will require to achieve stabilization. A shotgun slug for example, may only require a twist rate of 1-36 to stabilize, just about the slowest you will find. Light varmint bullets, which are usually shot at high velocities, require very little twist rate to stabilize compared to heavier counterparts.

Heavy match bullets as we would expect, require much faster twist rates to stabilize in the same bore size. A 22 caliber 95 grain Sierra MatchKing for example, requires a twist rate of 1-6.5 or faster to stabilize. A 35 grain V-Max in 22 caliber on the other hand, only requires a 1-12 or even a 1-14 twist rate to stabilize.

What Happens When There’s Not Enough Twist?

As discussed previously, a bullet needs a certain amount of twist or spin to fly straight and accurately down range. But what happens to the projectile if the minimum twist rate for its specific design is not met?

If a bullet is not being spun fast enough, there is one major sign to tell…… Keyholing. Keyholing is the term used to describe a bullet that leaves the muzzle of a barrel that is not able to stabilize in the air. Without enough stabilization, the bullet is not able to spin like a football.

Fortunately, this issue is almost always easy to diagnose. Without enough stabilization, the bullets will almost always strike the target length wise, creating what appears to be a “keyhole” type shape. As you can imagine however, having no stabilization equates to having no consistency. This means that although it is easy to diagnose, you may miss the paper, in which case you might not realize the issue. 

Keyholing is most prevalent with long, heavy for caliber bullets in relatively slow twist rates. A 62-grain green tip (not very heavy for caliber) for example, will not stabilize in a 1-12 twist barrel due to its slow nature.

Can I Have Too Much Twist?

Although we have determined that a bullet needs a minimum amount of spin to stabilize, there is a point at which this spin can become too great. This is generally called over stabilization, which occurs when a twist rate is too fast for a specific bullet type. It can be challenging to determine if your bullets are experiencing too much twist, but there are a few signs that may give it away.

The first and most noticeable way to diagnose over stabilization, is if the bullet is coming apart out of the barrel. Light varmint bullets fired at extremely high velocities are particularly at risk for this issue. Let’s look at a 22-250 shooting a 45 grain at about 4000 fps for example.

This specific bullet can stabilize in a 1-14 twist, but if we were to shoot it out of a 1-7 twist, the bullet would most likely come apart outside the bore. If we think about what is happening, doubling the speed at which the bullet is spinning is placing an extreme amount of force on the construction of the bullet.

If a bullet construction is already designed to be fragile (most varmint bullets), this increased force will almost always end in pieces. Solid copper bullets are much stouter in design, so you may not notice any separation in these instances, although you probably won’t be getting a desirable group size.

In fact, not getting a proper group size is the next sign that your bullet may be over stabilized. This one can be much harder to diagnose, but if a bullet is experiencing too much twist, you may notice larger groups than expected, especially at extended ranges. 

A bullet experiencing over-stabilization can experience the nose rotating into a sub-optimal position. This positioning could cause the bullet to fly at a slightly different trajectory which translates to a larger group size. This scenario, however, is very hard to diagnose.

Conclusion

When buying a new rifle, twist is one of the most important and overlooked factors. Twist rate plays a vital role in the performance of your rifle by dictating the specific bullets a rifle can stabilize. When looking at twist rate, it is important to consider what the rifle is going to be used for.

Rifles intended for heavy match bullets benefit from fast twist rates whereas rifles intended for light varmint bullets prefer slow twist rates. In general, however, most factory rifles will use a “middle of the road” twist rate that can stabilize a wide range of bullets. 

--Banana Ballistics