What is twist rate

A twist rate indicates that the bullet will undergo a rotation once every seven inches, which, as you might imagine, is a much faster spin. There are a wide variety of bullet weights available, anywhere between 30 and 80 grains, in the extremes of the 5. Want to shoot a little lighter? Go Little heavier? Take another measurement, subtract it from the first, and that will be the denominator of your twist rate. For purposes of clarity, I consent to Athlon's collection, storage, processing, and transfer of my Personal Data and Non-Personal Data as defined in the Privacy Policy for the purpose of signing up for the email newsletter.

It utilizes an interchangeable barrel and quick takedown technology. The system […]. Comment s. Click to share on Facebook Opens in new window Click to share on Twitter Opens in new window Click to share on Pinterest Opens in new window Click to email this to a friend Opens in new window. Stay in the know with the latest from the Ballistic newsletter Sign-up today! Sign up for our newsletter Sign Up. Up Next. Athlon Outdoors Network. Post was not sent - check your email addresses!

The nature of a projectile like 5. Remember when I mentioned the center of pressure vs the center of gravity above? When the bullet impacts, the dramatic increase in drag moves the center of pressure way in front of the center of gravity. At the same time, the deceleration and reduction in RPM from friction further destabilize the bullet.

It has little to do with how stable it was flying beforehand. A slight angle of attack on impact may speed up the tumbling effect, though. This angle of attack is a slight deviation of the tip of the bullet from the centerline of flight. This happens naturally during spin stabilization, but the tip will be further away from the center at different times.

If you want to read more about how bullets actually wound and kill, check out my article on terminal ballistics. Now to the easy button. Based on the formulas above, I put together some charts to help you in the future.

I calculated each of these using the same baseline velocity of fps and environmental factors used in Miller. I also brought in the 90 gr SMK popular with the. I thought the results were interesting for the 30 cal. The bullet seems pretty stable across all of the popular. Shot at subsonic velocities, BLK is very quiet and packs a punch. Your mileage may vary, of course, depending on your experiences. Like the. Since the aerodynamics of bullet flight want to make the projectile tumble end over end, we need a way to stabilize it.

Spin is imparted by the rifling grooves down your barrel. The rate at which these grooves curve around the bore, the twist rate, imparts many thousands of RPM to the bullet.

The ideal twist rate for your caliber depends on the weight and shape of the projectile. There are a lot of formulas out there for figuring out the right twist rate, and I walked through the important ones with you. I also provided a few links to online calculators that do a great job. Lastly, I left you with a few charts to work with in the future. If you have any more questions or want any more charts for specific calibers, let me know in the comments.

This site uses Akismet to reduce spam. Learn how your comment data is processed. I think a chart of 6. For example, 6. Only drawback was that it needed a long action. After some quick googling, it seems to be hit or miss. I recently bought a Carl Gustafs M96 Long Rifle ie 29in bbl and have picked up a couple different gr bullets from hornady, remington and Speer, as well as some hornady gr RN. I should be able to get the s up to about fps and the s to around fps.

The M96 has a twist rate of mm 7. So I worked up some quick back-of-the-napkin numbers for 6. I ran it from gr up through gr as you might find in the long action 6.

I thought it was interesting that the Nosler behaved differently. Intelligent information provided with clarity — illustrates understanding and the ability to communicate effectively. Thank you for this. In general, my set-up prefers the grain range of bullet — most likely to go with the 69 grain Sierra. Average 5-shot groups over the past year have an average MOA of 0. Thanks — pleased with the Savage.

I shoot many calibers and 54 cal round ball out of a twist rate of 1in 72 and at yard with a 12 inch gong and can make it ring often.

The British LA1 uses a Excellent example! Again, I think most people overthink the whole overtwist issue. Is there some situation where running a too-fast twist going to be a detriment? Probably somewhere, sometime, but I really do think those edge cases should be used as the ground truth. First off, thank you for all the great articles that you have written. Where I am from, a lot of old timers said that it is dangerous to shoot the M out of the old M16 barrels. They said that doing so would result in a catastrophic blow-out.

My question is, where is this idea coming from? Hi John, thanks for coming by and asking! The old That … Read more ». Can you explain how this happens in the table, since for the bullet diameter d and length L is the same regardless of the bullet weight?

But the length of the bullet does change as the mass increases. Since it cannot increase in diameter it always has to be. So as m increases for the same bullet dimensions and twist rate, the stability factor goes up. But in your table for twist, it goes down. Bullet mass can change without affecting the bullet dimensions, for example by varying the mix of metals that make it up for example, more copper, less lead.

Are you reading the table vertically or horizontally? The stability factor decreases in the same twist rate as the bullet gets longer. I only listed the most commonly discussed bullets, and there are a lot out there.

That said, even the all-copper Barnes bullets tend to need faster twist rates as they are less dense for weight and so are usually longer. The dimensions of the bullet do not stay the same as the bullet gets heavier, though. I would have to go back and revisit the JBM bullet library for specifics, but your example is correct. An increasing twist will hardly affect the accuracy except for extreme cases. However, a decreasing twist rate will reduce accuracy significantly.

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.

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