Forums
New posts
Search forums
What's new
Articles
Latest reviews
Author list
Classifieds
Log in
Register
What's new
Search
Search
Search titles and first posts only
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
The science to twist rates
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Mikecr" data-source="post: 451769" data-attributes="member: 1521"><p>Bryan Litz(above) explains RPM relationships very well in his book. </p><p></p><p>My perspective on twist requirements center on displacement as the dominant overturning cause. It is also not the truth in that it will also fail tests. But it passes way more tests than RPM rules of thumb, given a set bullet design(it's Cg to predicted Cp arm).</p><p>By displacement, I'm really talking drag throughout it.</p><p>And my perspective here is a way of mitigating errors in twist choices.</p><p></p><p>I see a turn of a bullet(it's inertia) as overcoming x.xx" of displacement(overturning cause). Increasing velocity really doesn't change this model. A 12:1 twist barrel causes 1 turn per 12" at the muzzle, regardless of velocity. And a bullet going down range(slowing) displaces fewer and fewer inches per turn to overcome, allowing it's gyroscopic stabilty to climb continually. The twist rate can go from 12:1 at the muzzle to a relative 6:1 by 1kyds. Sg might end up 3-5.0 by then..</p><p>This holds for dynamically stable bullets still above transonic.</p><p>As air density goes up,(or drag goes up), the relative displacement goes up, and 12:1 actual turns into a relative 13 or 14:1 in free flight (in my model).</p><p></p><p>In reality, bullet inertia must overcome other moments, and it can also actually be a source of moments. Muzzle release is a big one, hitting your target is another big one,, traversing transonic, imbalances and flaws, etc.. Alot of things going on that could combine to overtake displacement as dominant, but that's not common these days(much less consistant).</p><p></p><p>I think the intent of recommended twist rates should be taken in this context, even though there is more to it.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 451769, member: 1521"] Bryan Litz(above) explains RPM relationships very well in his book. My perspective on twist requirements center on displacement as the dominant overturning cause. It is also not the truth in that it will also fail tests. But it passes way more tests than RPM rules of thumb, given a set bullet design(it's Cg to predicted Cp arm). By displacement, I'm really talking drag throughout it. And my perspective here is a way of mitigating errors in twist choices. I see a turn of a bullet(it's inertia) as overcoming x.xx" of displacement(overturning cause). Increasing velocity really doesn't change this model. A 12:1 twist barrel causes 1 turn per 12" at the muzzle, regardless of velocity. And a bullet going down range(slowing) displaces fewer and fewer inches per turn to overcome, allowing it's gyroscopic stabilty to climb continually. The twist rate can go from 12:1 at the muzzle to a relative 6:1 by 1kyds. Sg might end up 3-5.0 by then.. This holds for dynamically stable bullets still above transonic. As air density goes up,(or drag goes up), the relative displacement goes up, and 12:1 actual turns into a relative 13 or 14:1 in free flight (in my model). In reality, bullet inertia must overcome other moments, and it can also actually be a source of moments. Muzzle release is a big one, hitting your target is another big one,, traversing transonic, imbalances and flaws, etc.. Alot of things going on that could combine to overtake displacement as dominant, but that's not common these days(much less consistant). I think the intent of recommended twist rates should be taken in this context, even though there is more to it. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
The science to twist rates
Top