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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Barrel twist
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<blockquote data-quote="Mikecr" data-source="post: 1170198" data-attributes="member: 1521"><p>Putting bullet center of mass(Cg) further behind center of pressure(Cp) does not make it more stable.</p><p>But reduced drag can.</p><p></p><p>Better to remember what twist rate is; displacement per turn -to overcome that displacement.</p><p>So 8:1 twist rate is 8" of displacement by each turn.</p><p>Now displacement itself is relative to air density and resultant drag by design.</p><p>Therefore every aspect of a bullet's design that contributes to drag -affects stability.</p><p></p><p>Then you have disturbances to overcome(moments).</p><p>Gyroscopic turns are not the only way to overcome disturbances. Center of gravity -vs- center of pressure relationship is another. And this design attribute contributes toward or against stability.</p><p>This is the moment arm that makes longer bullets more of a challenge to stabilize, even while drag is reduced(because their Cg is usually further behind their Cm).</p><p>Another factor commonly overlooked is quality of bullet release. Too short of a barrel for the cartridge capacity leads to extreme muzzle pressures, which do nothing good for clean release of BT bullets.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 1170198, member: 1521"] Putting bullet center of mass(Cg) further behind center of pressure(Cp) does not make it more stable. But reduced drag can. Better to remember what twist rate is; displacement per turn -to overcome that displacement. So 8:1 twist rate is 8" of displacement by each turn. Now displacement itself is relative to air density and resultant drag by design. Therefore every aspect of a bullet's design that contributes to drag -affects stability. Then you have disturbances to overcome(moments). Gyroscopic turns are not the only way to overcome disturbances. Center of gravity -vs- center of pressure relationship is another. And this design attribute contributes toward or against stability. This is the moment arm that makes longer bullets more of a challenge to stabilize, even while drag is reduced(because their Cg is usually further behind their Cm). Another factor commonly overlooked is quality of bullet release. Too short of a barrel for the cartridge capacity leads to extreme muzzle pressures, which do nothing good for clean release of BT bullets. [/QUOTE]
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Barrel twist
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