a bullet twisting after leaving a barrel

What Is Twist Rate? A Brief And Simple Explanantion

Along with learning the practical elements of shooting comes the bewildering array of lingo that you have to be familiar with.

Across the land, shooters congregate and discuss every detail they prefer with respect to their firearm. Rifle shooters in particular will discuss the twist rate, but what is a twist rate?

The twist rate is simply the rate at which the bullet spins in a barrel. It’s represented as a revolution per amount of inches. For instance, a barrel with a 1:7″ twist means the bullet completes one revolution every 7 inches of barrel length.

You may have noticed that some rifles shoot pretty well with some loads but perform dismally with others. It all boils down to the load specification. Many shooters get mixed on what attributes to look for and why they are essential. 

a bullet twisting after leaving a barrel

One of the main talking points, especially on the shooting range, is the twists rate. 

Do you choose a load with a high or low twist rate? Keep reading to find out how this key concept affects the performance of a rifle.

So, What Exactly Is Twist Rate?

The twist rate is the rate at which the rifle barrel spins the bullet. 

The rate of spin in the rifle barrel is expressed in inches per turn. A barrel with a 1:10 twist means that the rifle will twist the bullet one revolution in 10 inches, and a 1:5″ twist will twist one revolution every 5 inches.

pictorial diagram of twist rate

Standard AR-15 rifles have a twist rate of around 1:7 or1:8. 

A 1:8 twist barrel is faster than a 1:10 twist rate. For instance, a 1:8 twist barrel will spin a bullet faster than a 1:10 at the same velocity. Generally, quick twist barrels are designed for longer bullets while shorter bullets are used in slower twist barrels.

The twist rate also determines the stability of a bullet when fired from any rifle. If the twist recommendation is 1:10, a bullet will be stable in a gun with a twist rate of 1:10 or faster. If the twist rate is not enough, the bullet will be unstable.

Does The Twist Rate Affect Accuracy?

You might be wondering why the barrel twist rate is so important. 

Well, the rate is essential in determining bullet accuracy. The barrel twist stabilizes the bullet by starting the bullet spinning at a specific rate.

A dirty barrel reduces the twist rate as the rifling doesn’t have its full effect on the round. Additionally, a powerful cartridge can propel the round too fast for the barrel, and the rifling doesn’t have the chance to start spinning the bullet.

A constant rate provides the utmost accuracy. An increasing twist will hardly affect the accuracy except for extreme cases. However, a decreasing twist rate will reduce accuracy significantly. The bullet doesn’t spin properly and starts to tumble in flight.

A proper spin makes the bullet more stable as it cuts through the air. Inflight stability enhances accuracy, especially in long-range shots.

From the foregoing, a constant twist rate is vital. So which is the proper rate? Fortunately, any reputable barrel maker or gunsmith will give you the right rate for standard bullet and caliber weights.

The Greenhill formula comes in handy if you need to calculate the proper rate.

the greenhill formula

For most standard cartridges the formula is T=150(d/r)

T is the twist rate, d is the diameter, and r is the bullet ratio to the diameter.

Cartridges that produce a muzzle velocity above 2800 fps the formula is T= 180 (d/r)

Here is another critical point. Overstabilization is not suitable for accuracy. Usually, overstabilization occurs as a result of a twist rate that is too fast. An over stabilized bullet follows a downward arc with the tip pointing upwards.

It is worth noting that the bullet weight does not affect the barrel twist rate. 

The bullet length dictates the barrel rifling twist. Generally, the longer the bullet is, the heavier it is. This means there is more surface area of the bullet the connects with the rifling. Longer bullets require faster rifling twist to stabilize the bullet in flight.

Next time you set out to buy a rifle, save yourself all the trouble and ask the gunsmith the right gun for bullets you plan to use. Firearm manufacturers spend a lot of time, matching barrel twist rates to ammunition.

a rifle barrel showing rifling

A Faster Or Slower Twist Rate?

The question is probably lingering in your mind as to whether you should opt for a slower or faster rate. 

Well, the reasonable twist rate depends on the bullet you plan to use. A 1:8 twist rate is faster than 1:10, while 1:12 is slower than 1:10. Generally, shorter bullets use slower twist barrels while longer bullets use fast twist barrels.

The projectile you are shooting and the twist should complement each other to attain optimal performance. 

Typically, the United States military use rifles with a twist rate of 1:7. This aggressive rate is vital in stabilizing ammunition used in combat.

Most civilian rifles are used for sporting activities. Private citizens can, therefore, access AR rifles with varying twist rates. Most of these modern AR-style rifles come with a twist rate ranging from 1:7 to 1:9. You can, however, get a slower AR rifle with a 1:12 rate.

A barrel with 1:8 twists is the most versatile. It’s the most flexible and stabilizes projectile weighing 80 grains most effectively. What more is that it does not over stabilize light bullets.

Barrels with a twist rate of 1:9 are suitable for stabilizing mid-weight and light bullets ranging from 45 to 77 grains.

a rifle barrel showing rifling

Spin It

The barrels of modern handguns and rifles come with the spiraling groove called rifling, but it was invented in the late 15th Century. Rifling the firearm barrel is what causes the bullet to spiral, but the rate of twist will depend upon the bullet speed and bullet length.

It spins the bullet as it moves along the barrel and through the air toward the target. A tight spiral pattern in the barrel makes the bullet to turn faster in the air, so a high twist rate has been applied.

Rifle makers usually provide the ideal rate for cartridges intended for handguns and hunting rifles. 

Final Thoughts

Understanding twist rates can help you enhance your shooting performance. 

The twist rate is one of the factors that affect your shooting accuracy. 

Note that barrel length and speed of the bullet influence bullet stability. However, increasing the barrel length will not enhance the stability if the twist rate is low. 

Matching bullet weight with the right barrel twist will take your shooting a notch higher, and it’s a good reason for choosing a manufacturer’s ammunition with their firearm.

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