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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6.5x55 se twist rate
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<blockquote data-quote="tim_w" data-source="post: 1347985" data-attributes="member: 11132"><p>Did want to add, that all other things being equal, weight alone of the bullet does effect stability and BC even with the offset of vel. Hypothetically if you took a formed bullet jacket of the same dimensions and filled one with copper, another with lead, and the last with tugnsten you would need the most twist rate to stabilize the copper to 1.5 and a slower twist for the lead and even slower twist yet for the highly dense and thus significantly heavier tungsten core.</p><p></p><p>Tungsten is 1.7? denser than lead which is 1.3ish?? to copper. Forget the jacket weight but take whatever vld/hybrid shape bullet in lead say 6.5 140 hybrid as its the discussion point: (pretending there is no jacket weight) (tungsten only added to show an extreme but still doable possibility)</p><p></p><p>Copper: 107gr</p><p>Lead: 140gr.</p><p>Tungsten: 238gr.</p><p></p><p>Plug that into a very basic stability calculator of JBM which does not account for shift in mass and actually bullet shape changes (as they are all the same design is not a real factor). </p><p></p><p>As the subject is 6.5 Berger EOL 140gr which is 1.403 OAL and the 8.6 barrel we can go with that.</p><p></p><p>Caliber: .260/6.5mm</p><p>Length 1.5"</p><p>Vel 3000fps</p><p>Twist rate: 8.6</p><p>Bullet weights:</p><p></p><p>107 gr: 1.019 (Increasing vel to 3300fps increased stability factor to: 1.052)</p><p>140 gr: 1.334</p><p>238 gr: 2.267 (decreasing vel to 2500fps decreased stability factor to: 2.133)</p><p></p><p>BTW changing the twist rate to 8.0 @ 3K fps gave a stability factor of: 1.541</p><p></p><p>Seems like those numbers are pretty spot on for the most part. 8.6 to 8.0= 1.334 to 1.541 @ standard enviormentals. So while a real EOL 140 looks like it will stablize in those conditions the same bullet in copper would not even driven to its higher vel.</p></blockquote><p></p>
[QUOTE="tim_w, post: 1347985, member: 11132"] Did want to add, that all other things being equal, weight alone of the bullet does effect stability and BC even with the offset of vel. Hypothetically if you took a formed bullet jacket of the same dimensions and filled one with copper, another with lead, and the last with tugnsten you would need the most twist rate to stabilize the copper to 1.5 and a slower twist for the lead and even slower twist yet for the highly dense and thus significantly heavier tungsten core. Tungsten is 1.7? denser than lead which is 1.3ish?? to copper. Forget the jacket weight but take whatever vld/hybrid shape bullet in lead say 6.5 140 hybrid as its the discussion point: (pretending there is no jacket weight) (tungsten only added to show an extreme but still doable possibility) Copper: 107gr Lead: 140gr. Tungsten: 238gr. Plug that into a very basic stability calculator of JBM which does not account for shift in mass and actually bullet shape changes (as they are all the same design is not a real factor). As the subject is 6.5 Berger EOL 140gr which is 1.403 OAL and the 8.6 barrel we can go with that. Caliber: .260/6.5mm Length 1.5" Vel 3000fps Twist rate: 8.6 Bullet weights: 107 gr: 1.019 (Increasing vel to 3300fps increased stability factor to: 1.052) 140 gr: 1.334 238 gr: 2.267 (decreasing vel to 2500fps decreased stability factor to: 2.133) BTW changing the twist rate to 8.0 @ 3K fps gave a stability factor of: 1.541 Seems like those numbers are pretty spot on for the most part. 8.6 to 8.0= 1.334 to 1.541 @ standard enviormentals. So while a real EOL 140 looks like it will stablize in those conditions the same bullet in copper would not even driven to its higher vel. [/QUOTE]
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6.5x55 se twist rate
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