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
Bullet Stabilization Questions
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="MAX" data-source="post: 30762" data-attributes="member: 184"><p>michele, in regards your .308 experience:</p><p></p><p>I'm not expert in this and am shooting from the hip by not researching your particulars. That said:</p><p></p><p>1. BC does not have particular effect on gyroscopic stability(GS). GS is a function of twist/bullet length. GS may exist in one atmospheric circumstance and not in another, even with the same bullet/twist and velocity, due to differences in air density.</p><p></p><p>2. GS is inverse to velocity as the bullet travels downrange. This is because of reduced aerodynamic loads and resulting moments, and the fact that rotational velocity of the bullet decays VERY SLOWLY. Because GS is inverse to velocity, so to is tractibility(bullet nosing over to follow the flight path). This contributes to a reduced BC as does the increase in coefficient of drag due to Mach number decay.</p><p></p><p>3. Highly stabilized bullets suffer more from yaw of repose that bullets with low GS. As I understand it, a point can be reached in high GS scenarios that will cause a bullet to tumble because of the issue of yaw of repose and intractibility. In other words, it gets a bit too much sideways, and aerodynamic moments overcome GS. </p><p></p><p>Apparently there are two paths to the same result. Read on:</p><p></p><p>4. There has been discussion here in the past that stipulated bullets with low GS may tumble due to turbulence associated with transonic flowfields. I have not read authoritative sources on that issue, and remain undecided.</p><p></p><p>5. Speculation: Your 1:12 twist may be a bit slow for the "cold dense air" and your resulting GS low. It is common for bench shooters to use different twist rates at different altitudes due to this. Harold Vaughn discusses this at some length in his book, regarding the 6mmPPC and the use of 14" or 16" twist rates for a FB spitzer of 60 grains or so. By adding a little bit of velocity, your bullet may have had a bit higher GS or remained supersonic to POI, or both.</p><p></p><p>In any case, BC has no direct relation to GS. The cause of your bullets getting sideways lays elsewhere. </p><p></p><p>If I spoke incorrectly on this, I'm sure one of the guys or gals here will correct me, but that is MY take on your experience. The Physics of Exterior Ballistics is intolerant of extremes. JMO</p></blockquote><p></p>
[QUOTE="MAX, post: 30762, member: 184"] michele, in regards your .308 experience: I'm not expert in this and am shooting from the hip by not researching your particulars. That said: 1. BC does not have particular effect on gyroscopic stability(GS). GS is a function of twist/bullet length. GS may exist in one atmospheric circumstance and not in another, even with the same bullet/twist and velocity, due to differences in air density. 2. GS is inverse to velocity as the bullet travels downrange. This is because of reduced aerodynamic loads and resulting moments, and the fact that rotational velocity of the bullet decays VERY SLOWLY. Because GS is inverse to velocity, so to is tractibility(bullet nosing over to follow the flight path). This contributes to a reduced BC as does the increase in coefficient of drag due to Mach number decay. 3. Highly stabilized bullets suffer more from yaw of repose that bullets with low GS. As I understand it, a point can be reached in high GS scenarios that will cause a bullet to tumble because of the issue of yaw of repose and intractibility. In other words, it gets a bit too much sideways, and aerodynamic moments overcome GS. Apparently there are two paths to the same result. Read on: 4. There has been discussion here in the past that stipulated bullets with low GS may tumble due to turbulence associated with transonic flowfields. I have not read authoritative sources on that issue, and remain undecided. 5. Speculation: Your 1:12 twist may be a bit slow for the "cold dense air" and your resulting GS low. It is common for bench shooters to use different twist rates at different altitudes due to this. Harold Vaughn discusses this at some length in his book, regarding the 6mmPPC and the use of 14" or 16" twist rates for a FB spitzer of 60 grains or so. By adding a little bit of velocity, your bullet may have had a bit higher GS or remained supersonic to POI, or both. In any case, BC has no direct relation to GS. The cause of your bullets getting sideways lays elsewhere. If I spoke incorrectly on this, I'm sure one of the guys or gals here will correct me, but that is MY take on your experience. The Physics of Exterior Ballistics is intolerant of extremes. JMO [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet Stabilization Questions
Top