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
220 Swift, twist rate, barrel length
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: 1152163" data-attributes="member: 1521"><p>This is absolute rubbish. In fact, a lie.</p><p></p><p>Bart, the displacement I'm talking about is inches of air density, per turn, to counter the overturning moment(drag). It's relative because air density is relative to conditions, and the displacement per turn decreases as the bullet slows down range.</p><p>Bullet stability requirements(twist requirement) are in displacement per turn (like 12:1), and this is relative to a displacement standard(Std Armory, Std.Metro, Std.ICAO) and drag within it.</p><p></p><p>Muzzle velocity and RPM notions for stability fail tests right off the bat, as they are tied to TIME instead of displacement. Notice no bullet makers declare stability requirements using velocity or RPMs. They use twist at a specified sea level std. atmosphere. This is displacement -per turn -to overcome it.</p><p></p><p>It's been suggested here that great velocities from a 220 swift will overcome realities of stability requirements. This is not true at all. Displacement holds regardless of velocity/time through it.</p><p>For example; 69gr Sierra SMK, a pretty common bullet that needs a 10:1 twist under any SL conditions. In 14tw, even 10,000fps MV(514,000rpm) would not stabilize this bullet. Even if it didn't blow up(which it would), It would still tumble immediately.</p><p>An 80gr SMK in 14tw would not stabilize at ANY viable velocity, RPM, or atmospheric condition.</p><p>Same with a 75gr Berger VLD. These need 8" of displacement per turn, not 14".</p><p>Up in the 90gr bullets, you need 6.5-7:1.</p><p></p><p>A 15:1 22cal barrel WILL NOT shoot "all .224 bullets well"......</p><p></p><p>-14tw is good for 50-52gr</p><p>-12tw is good for 55-60gr</p><p>-10tw gets by for 60-70gr bullets at higher altitudes</p><p>-LR target bullets >65gr will need 8tw, all the way to 6.5tw</p><p></p><p>-All regardless of cartridge</p></blockquote><p></p>
[QUOTE="Mikecr, post: 1152163, member: 1521"] This is absolute rubbish. In fact, a lie. Bart, the displacement I'm talking about is inches of air density, per turn, to counter the overturning moment(drag). It's relative because air density is relative to conditions, and the displacement per turn decreases as the bullet slows down range. Bullet stability requirements(twist requirement) are in displacement per turn (like 12:1), and this is relative to a displacement standard(Std Armory, Std.Metro, Std.ICAO) and drag within it. Muzzle velocity and RPM notions for stability fail tests right off the bat, as they are tied to TIME instead of displacement. Notice no bullet makers declare stability requirements using velocity or RPMs. They use twist at a specified sea level std. atmosphere. This is displacement -per turn -to overcome it. It's been suggested here that great velocities from a 220 swift will overcome realities of stability requirements. This is not true at all. Displacement holds regardless of velocity/time through it. For example; 69gr Sierra SMK, a pretty common bullet that needs a 10:1 twist under any SL conditions. In 14tw, even 10,000fps MV(514,000rpm) would not stabilize this bullet. Even if it didn't blow up(which it would), It would still tumble immediately. An 80gr SMK in 14tw would not stabilize at ANY viable velocity, RPM, or atmospheric condition. Same with a 75gr Berger VLD. These need 8" of displacement per turn, not 14". Up in the 90gr bullets, you need 6.5-7:1. A 15:1 22cal barrel WILL NOT shoot "all .224 bullets well"...... -14tw is good for 50-52gr -12tw is good for 55-60gr -10tw gets by for 60-70gr bullets at higher altitudes -LR target bullets >65gr will need 8tw, all the way to 6.5tw -All regardless of cartridge [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
220 Swift, twist rate, barrel length
Top