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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
The science to twist rates
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<blockquote data-quote="BryanLitz" data-source="post: 451576" data-attributes="member: 7848"><p>Here's a full answer:</p><p><a href="http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf" target="_blank">http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf</a></p><p></p><p>The short answer is that you can think of twist rates in terms of 'calibers per turn', and some of the mystery goes away.</p><p></p><p>Most heavy high BC bullets require about 32 calibers per turn to stabilize.</p><p></p><p>In .22 cal, this equates to a twist rate of 1:7.2"</p><p>In .244 cal, this equates to a twist rate of 1:7.8"</p><p>In .257 cal, this equates to a twist rate of 1:8.2"</p><p>In .264 cal, this equates to a twist rate of 1:8.5"</p><p>In .277 cal, this equates to a twist rate of 1:8.9"</p><p>In .284 cal, this equates to a twist rate of 1:9.1"</p><p>In .308 cal, this equates to a twist rate of 1:9.9"</p><p>In .338 cal, this equates to a twist rate of 1:10.8"</p><p></p><p>So as you can see, the twist rate in inches per turn gets slower as the caliber is larger, but the physics of scale dictate that the bullet needs a given 'caliber per turn' which applies universally to all calibers.</p><p></p><p>Note the .257 and .277 calibers require twist rates that are much faster than commonly available in those calibers. As a result, those calibers are limited to shooting bullets that are not as proportionally long and heavy as those in other calibers.</p><p></p><p>The link above goes into greater detail about stability near the end of the article.</p><p></p><p>Take care,</p><p>-Bryan</p></blockquote><p></p>
[QUOTE="BryanLitz, post: 451576, member: 7848"] Here's a full answer: [url]http://www.appliedballisticsllc.com/index_files/Understanding_part1.pdf[/url] The short answer is that you can think of twist rates in terms of 'calibers per turn', and some of the mystery goes away. Most heavy high BC bullets require about 32 calibers per turn to stabilize. In .22 cal, this equates to a twist rate of 1:7.2" In .244 cal, this equates to a twist rate of 1:7.8" In .257 cal, this equates to a twist rate of 1:8.2" In .264 cal, this equates to a twist rate of 1:8.5" In .277 cal, this equates to a twist rate of 1:8.9" In .284 cal, this equates to a twist rate of 1:9.1" In .308 cal, this equates to a twist rate of 1:9.9" In .338 cal, this equates to a twist rate of 1:10.8" So as you can see, the twist rate in inches per turn gets slower as the caliber is larger, but the physics of scale dictate that the bullet needs a given 'caliber per turn' which applies universally to all calibers. Note the .257 and .277 calibers require twist rates that are much faster than commonly available in those calibers. As a result, those calibers are limited to shooting bullets that are not as proportionally long and heavy as those in other calibers. The link above goes into greater detail about stability near the end of the article. Take care, -Bryan [/QUOTE]
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