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Rifles, Reloading, Optics, Equipment
Reloading
Bullet stability
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<blockquote data-quote="Hugnot" data-source="post: 2824785" data-attributes="member: 115658"><p>The Miller stability or Sg calculator is only an estimator providing a ratio, like over 1.0 having neutral stability & 1.5 having adequate stability.</p><p></p><p>The Miller method is widely accepted and is used by Berger & JBM. Berger uses an altitude pressure table vs. actual barometric pressures. It (Miller) does not consider large cavities in bullets like the 107 grain 6.5 Sierra hpbt that appears to have close to 20% void at tip (material density). Plastic tips are factored in by an operation like (H25 - H26 / H23) ^2, as shown in the calculation spread sheet.</p><p></p><p>Sg values increase down range as bullet velocity decreases rapidly and effects such as yawing & pitching decrease while bullet revs decrease very slowly with TOF being short (spinning like crazy, lots of RPM's like over 300K in some cases)</p><p></p><p>From Hornady;</p><p></p><p>"The pitch and yaw angle is continually getting smaller because the bullet is dynamically stable."</p><p></p><p>This makes Sg values increase as velocity decreases.</p><p></p><p>Velocity only has a minor effect on Sg values, like:</p><p></p><p>[ATTACH]464841[/ATTACH]</p><p></p><p>Note the Sg value creeps up from 1.65 to 1.68 with a 150 fps velocity increase - no big deal.</p><p></p><p>Form factor is another important consideration giving rise to lighter bullets that can be driven faster, like:</p><p></p><p>[ATTACH]464843[/ATTACH]</p><p></p><p>I like the .224 75 grain ELDM in my 7.7 twist .22-.250's because it provides good ballistics at low cost, like under $30 for 100 & powder charges in the mid 30 grain range. The .224 80 grain ELDM has higher G7 BC values but cannot be driven as fast, however the 80's give slightly better numbers using Hornady's 4DOF program with ranges up to 1000 with 100 fps slower MV's.</p><p></p><p>I have no plans to shoot some real big beast with my little .22-.250 with 75 grain ELDM bullets but I have plans for some programming compiler on my computer so I can quit messing with spread sheets like (H25 - H26 / H23) ^2</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2824785, member: 115658"] The Miller stability or Sg calculator is only an estimator providing a ratio, like over 1.0 having neutral stability & 1.5 having adequate stability. The Miller method is widely accepted and is used by Berger & JBM. Berger uses an altitude pressure table vs. actual barometric pressures. It (Miller) does not consider large cavities in bullets like the 107 grain 6.5 Sierra hpbt that appears to have close to 20% void at tip (material density). Plastic tips are factored in by an operation like (H25 - H26 / H23) ^2, as shown in the calculation spread sheet. Sg values increase down range as bullet velocity decreases rapidly and effects such as yawing & pitching decrease while bullet revs decrease very slowly with TOF being short (spinning like crazy, lots of RPM's like over 300K in some cases) From Hornady; "The pitch and yaw angle is continually getting smaller because the bullet is dynamically stable." This makes Sg values increase as velocity decreases. Velocity only has a minor effect on Sg values, like: [ATTACH alt="Screenshot (674).png"]464841[/ATTACH] Note the Sg value creeps up from 1.65 to 1.68 with a 150 fps velocity increase - no big deal. Form factor is another important consideration giving rise to lighter bullets that can be driven faster, like: [ATTACH alt="Screenshot (660).png"]464843[/ATTACH] I like the .224 75 grain ELDM in my 7.7 twist .22-.250's because it provides good ballistics at low cost, like under $30 for 100 & powder charges in the mid 30 grain range. The .224 80 grain ELDM has higher G7 BC values but cannot be driven as fast, however the 80's give slightly better numbers using Hornady's 4DOF program with ranges up to 1000 with 100 fps slower MV's. I have no plans to shoot some real big beast with my little .22-.250 with 75 grain ELDM bullets but I have plans for some programming compiler on my computer so I can quit messing with spread sheets like (H25 - H26 / H23) ^2 [/QUOTE]
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