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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet RPM Per Inch Math Problem
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<blockquote data-quote="longestrange" data-source="post: 2100821" data-attributes="member: 75265"><p>If a barrel has a one in 12" twist, the bullet will rotate exactly once in 12" as it leaves the muzzle. If it has a 1 in 6" twist it will rotate exactly twice in 12" as it leaves the muzzle.</p><p>If that is true, then using 1 in 12 twist as an example:</p><p>At 3000 fps, the bullet will spin at 3000 revolutions per second (rps) as it starts out.</p><p>The energy involved is much more complicated. A larger diameter bullet will have more rotational energy and rotational momentum than a smaller diameter bullet of the same mass if they spin at the same rps. Also, as the bullet mushrooms it will increase in diameter and thus the rps will decrease due to something known as conservation of momentum. You can see this very clearly watching a figure skater. They start a spin with their legs and arms sticking out, but when they pull their legs and arms in they become a blur.</p><p>I'm too lazy to calculate the rotational energy, but very skeptical, given the small diameters of hunting bullets, that the spin contributes much to the damage - even if it is still rotating at the initial 3000 rps when it hits.</p></blockquote><p></p>
[QUOTE="longestrange, post: 2100821, member: 75265"] If a barrel has a one in 12" twist, the bullet will rotate exactly once in 12" as it leaves the muzzle. If it has a 1 in 6" twist it will rotate exactly twice in 12" as it leaves the muzzle. If that is true, then using 1 in 12 twist as an example: At 3000 fps, the bullet will spin at 3000 revolutions per second (rps) as it starts out. The energy involved is much more complicated. A larger diameter bullet will have more rotational energy and rotational momentum than a smaller diameter bullet of the same mass if they spin at the same rps. Also, as the bullet mushrooms it will increase in diameter and thus the rps will decrease due to something known as conservation of momentum. You can see this very clearly watching a figure skater. They start a spin with their legs and arms sticking out, but when they pull their legs and arms in they become a blur. I'm too lazy to calculate the rotational energy, but very skeptical, given the small diameters of hunting bullets, that the spin contributes much to the damage - even if it is still rotating at the initial 3000 rps when it hits. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet RPM Per Inch Math Problem
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