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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet Spin and Performance
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<blockquote data-quote="BryanLitz" data-source="post: 248421" data-attributes="member: 7848"><p>I'd like to point out some calculations regarding translational and rotational kinetic energy that are completely open for interpretation.</p><p></p><p>barrel/bullet:</p><p>A typical .30 caliber 155 grain bullet at a muzzle velocity of 3000 fps from a 1:13" twist barrel.</p><p></p><p>At the muzzle, this bullet will have 3095 ft-lb of translational kinetic energy.</p><p>At the muzzle, this bullet will have 7.7 ft-lb of rotational kinetic energy.</p><p></p><p>When the bullet has slowed to 1/2 it's original muzzle velocity, it will have 1/4 of it's original translational kinetic energy. This will happen somewhere around ~800 yards. At that distance, the rotational speed of the bullet will have decayed as well, but not as much as the forward velocity. The rotational velocity at this point will be about 80% of it's original value. So the numbers after the bullet has slowed to 1500 fps are:</p><p></p><p>Near 800 yards, the bullet will have 774 ft-lb of translational kinetic energy remaining.</p><p>Near 800 yards, the bullet will have 4.9 ft-lb of rotational kinetic energy remaining.</p><p></p><p>As I said, these numbers are open for interpretation. I can tell you what I think about them, but it's just speculation.</p><p></p><p>At the muzzle, the rotational KE is only 0.2% of the translational KE. This tell me that practically all of the damage done will be due to the bullet's forward motion, the spin being of little consequence to terminal performance.</p><p></p><p>At around 800 yards, the rotational KE has grown to 0.6% of the translational KE. This is 3X higher % than at the muzzle, but still an insignificant amount compared to the translational KE.</p><p></p><p>I am of the opinion that the rotational speed, and rotational KE of a bullet are of very little issue to that bullets ability to do damage on a target. I could be wrong (I've never done the test), but the numbers suggest that there is very little energy in rotation compared to forward motion.</p><p></p><p>-Bryan</p></blockquote><p></p>
[QUOTE="BryanLitz, post: 248421, member: 7848"] I'd like to point out some calculations regarding translational and rotational kinetic energy that are completely open for interpretation. barrel/bullet: A typical .30 caliber 155 grain bullet at a muzzle velocity of 3000 fps from a 1:13" twist barrel. At the muzzle, this bullet will have 3095 ft-lb of translational kinetic energy. At the muzzle, this bullet will have 7.7 ft-lb of rotational kinetic energy. When the bullet has slowed to 1/2 it's original muzzle velocity, it will have 1/4 of it's original translational kinetic energy. This will happen somewhere around ~800 yards. At that distance, the rotational speed of the bullet will have decayed as well, but not as much as the forward velocity. The rotational velocity at this point will be about 80% of it's original value. So the numbers after the bullet has slowed to 1500 fps are: Near 800 yards, the bullet will have 774 ft-lb of translational kinetic energy remaining. Near 800 yards, the bullet will have 4.9 ft-lb of rotational kinetic energy remaining. As I said, these numbers are open for interpretation. I can tell you what I think about them, but it's just speculation. At the muzzle, the rotational KE is only 0.2% of the translational KE. This tell me that practically all of the damage done will be due to the bullet's forward motion, the spin being of little consequence to terminal performance. At around 800 yards, the rotational KE has grown to 0.6% of the translational KE. This is 3X higher % than at the muzzle, but still an insignificant amount compared to the translational KE. I am of the opinion that the rotational speed, and rotational KE of a bullet are of very little issue to that bullets ability to do damage on a target. I could be wrong (I've never done the test), but the numbers suggest that there is very little energy in rotation compared to forward motion. -Bryan [/QUOTE]
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