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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet Spin and Performance
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<blockquote data-quote="Buffalobob" data-source="post: 248428" data-attributes="member: 8"><p>Bryan</p><p></p><p>I ran some calculation of the angular velocity of the jacket of a 308 and while that number is bigger it was only as a prelude to an other calculation. Would you check to see if my calculations are correct. It has been many years since I had to calculate anything in radians. </p><p></p><p>-----------------------------------------------------</p><p></p><p>Muzzle velocity = 3000 ft/ sec </p><p></p><p> Barrel 1-12 twist = 1 rev/ft = 1 radian</p><p></p><p>3000 R/s w</p><p></p><p>Linear</p><p></p><p>2pi x r = v</p><p></p><p>308 caliber r = 0.154 inches x 2 x 3.1416 x 3000/ sec / 12 inches = 241.9 fps</p><p></p><p></p><p></p><p></p><p>Let us look at a 308 bullet from a 1-12 twist barrel fired at 3000 fps.</p><p></p><p>It has a forward velocity of 3000 fps and an angular velocity of 3000 rev/ sec at the muzzle</p><p></p><p>Converting the angular velocity to a linear velocity of a particle in the outer jacket can be done because we know the radius of a 308 bullet is half the diameter. That translates to 241.9 feet per second.</p><p></p><p>If we spin the bullet with a 1-10 twist barrel then it has a linear velocity of 12/10 X 241.9 = 290 fps or a 20 percent increase.</p><p></p><p>If we take the original barrel and decrease the muzzle velocity by 10 percent then the angular velocity is decreased by 10 percent.</p><p></p><p>We can decrease the velocity by 20 percent and increase the twist by 20 percent and keep the angular velocity constant.</p><p></p><p>If we go to a larger caliber bullet and keep the same barrel and muzzle velocity then the angular velocity will be the same but the linear velocity is more because the increase in the radius. So the difference between a 308 bullet and a 338 bullet is a radius of 0.154 inches versus a radius of 0.169 inches or about a 10 percent increase in radius and so a 10 percent increase in linear velocity. </p><p></p><p>Nonetheless, no matter what twist nor what muzzle velocity nor what caliber, what I calculate is that the linear spin velocity is going to be about 10 percent of the forward velocity at the muzzle.</p><p></p><p>The only reason angular velocity is important is to calculate angular momentum.</p><p></p><p></p><p>----------------------------------------------------------------------</p></blockquote><p></p>
[QUOTE="Buffalobob, post: 248428, member: 8"] Bryan I ran some calculation of the angular velocity of the jacket of a 308 and while that number is bigger it was only as a prelude to an other calculation. Would you check to see if my calculations are correct. It has been many years since I had to calculate anything in radians. ----------------------------------------------------- Muzzle velocity = 3000 ft/ sec Barrel 1-12 twist = 1 rev/ft = 1 radian 3000 R/s w Linear 2pi x r = v 308 caliber r = 0.154 inches x 2 x 3.1416 x 3000/ sec / 12 inches = 241.9 fps Let us look at a 308 bullet from a 1-12 twist barrel fired at 3000 fps. It has a forward velocity of 3000 fps and an angular velocity of 3000 rev/ sec at the muzzle Converting the angular velocity to a linear velocity of a particle in the outer jacket can be done because we know the radius of a 308 bullet is half the diameter. That translates to 241.9 feet per second. If we spin the bullet with a 1-10 twist barrel then it has a linear velocity of 12/10 X 241.9 = 290 fps or a 20 percent increase. If we take the original barrel and decrease the muzzle velocity by 10 percent then the angular velocity is decreased by 10 percent. We can decrease the velocity by 20 percent and increase the twist by 20 percent and keep the angular velocity constant. If we go to a larger caliber bullet and keep the same barrel and muzzle velocity then the angular velocity will be the same but the linear velocity is more because the increase in the radius. So the difference between a 308 bullet and a 338 bullet is a radius of 0.154 inches versus a radius of 0.169 inches or about a 10 percent increase in radius and so a 10 percent increase in linear velocity. Nonetheless, no matter what twist nor what muzzle velocity nor what caliber, what I calculate is that the linear spin velocity is going to be about 10 percent of the forward velocity at the muzzle. The only reason angular velocity is important is to calculate angular momentum. ---------------------------------------------------------------------- [/QUOTE]
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