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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
bullet drop and scope leveling
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<blockquote data-quote="Bart B" data-source="post: 103201" data-attributes="member: 5302"><p>Rifle shooters have observed the phenomena of bullets going high-left and low-right for a century or more. If a left-hand twist is used it'll be low-left and high-right. It's most predominant with smallbore 22 rimfire rifles at 100 yards but gets less at shorter ranges. Some left-handed smallbore competitors cant their rifles about 35 degrees to the right so making windage only adjustments will compensate correctly in both axes. Centerfire rifle shooters have noticed it starting at about 800 yards and getting a bit worse at 1000 when some ammo types are used.</p><p></p><p>It's caused by cross winds putting different pressure under and over the bullet. A clockwise spinning bullet's surface pulls a wind from the right under it putting more pressure at that point so it moves left and up. The opposite happens with a wind from the left. Smallbore prone shooters will hold towards 4:15-o'clock when wind from the right picks up. Highpower shooters will hold off at 3:15-o'clock for a right wind pick up; the effect is much less than with 22 rimfire at 100 or 50 yards.</p><p></p><p>As for the coriolis effect on rifle bullets through 1000 yards, it may well exist. But it's so darned small and unimportant that none of the top highpower long range folks I know care about it nor get concerned about correcting for it. I once fired 30 rounds alternating between a 100- and 1000-yard target at 5 AM when the air was so calm and clear I could see bullet holes in the black at 1000 yards. The 15-shot groups at 100 and 1000 yards were centered for windage but the close one was some 40-odd inches high and straight up (measured with plumb line) from the aiming mark. Whatever drift effect there was didn't matter; it wasn't visible.</p><p></p><p>I don't remember much detail about gun aiming computers' corrections for latitude from my experiences in the late '50s. When I changed latitude, bearing and range values running tests on those marvelous mechanical monsters the gun orders in the horizontal plane also changed. How much was for precessional drift and how much was for the earth's rotation now escapes me. One can read about it by going to:</p><p> <a href="http://www.navweaps.com/index_tech/tech-056.htm" target="_blank">http://www.navweaps.com/index_tech/tech-056.htm</a> </p><p>then scrolling down to the section "Correcting for the Coriolis Effect." The greater the range the bigger the correction was. More information or large caliber ballistics including the projectile's drift caused by gyroscopic precession or Magnus Effect can be seen at</p><p> <a href="http://www.eugeneleeslover.com/USNAVY/CHAPTER-17-A.htm" target="_blank">http://www.eugeneleeslover.com/USNAVY/CHAPTER-17-A.htm</a></p></blockquote><p></p>
[QUOTE="Bart B, post: 103201, member: 5302"] Rifle shooters have observed the phenomena of bullets going high-left and low-right for a century or more. If a left-hand twist is used it’ll be low-left and high-right. It’s most predominant with smallbore 22 rimfire rifles at 100 yards but gets less at shorter ranges. Some left-handed smallbore competitors cant their rifles about 35 degrees to the right so making windage only adjustments will compensate correctly in both axes. Centerfire rifle shooters have noticed it starting at about 800 yards and getting a bit worse at 1000 when some ammo types are used. It’s caused by cross winds putting different pressure under and over the bullet. A clockwise spinning bullet’s surface pulls a wind from the right under it putting more pressure at that point so it moves left and up. The opposite happens with a wind from the left. Smallbore prone shooters will hold towards 4:15-o’clock when wind from the right picks up. Highpower shooters will hold off at 3:15-o’clock for a right wind pick up; the effect is much less than with 22 rimfire at 100 or 50 yards. As for the coriolis effect on rifle bullets through 1000 yards, it may well exist. But it’s so darned small and unimportant that none of the top highpower long range folks I know care about it nor get concerned about correcting for it. I once fired 30 rounds alternating between a 100- and 1000-yard target at 5 AM when the air was so calm and clear I could see bullet holes in the black at 1000 yards. The 15-shot groups at 100 and 1000 yards were centered for windage but the close one was some 40-odd inches high and straight up (measured with plumb line) from the aiming mark. Whatever drift effect there was didn’t matter; it wasn’t visible. I don’t remember much detail about gun aiming computers’ corrections for latitude from my experiences in the late ‘50s. When I changed latitude, bearing and range values running tests on those marvelous mechanical monsters the gun orders in the horizontal plane also changed. How much was for precessional drift and how much was for the earth’s rotation now escapes me. One can read about it by going to: [url="http://www.navweaps.com/index_tech/tech-056.htm"]http://www.navweaps.com/index_tech/tech-056.htm[/url] then scrolling down to the section “Correcting for the Coriolis Effect.” The greater the range the bigger the correction was. More information or large caliber ballistics including the projectile’s drift caused by gyroscopic precession or Magnus Effect can be seen at [url="http://www.eugeneleeslover.com/USNAVY/CHAPTER-17-A.htm"]http://www.eugeneleeslover.com/USNAVY/CHAPTER-17-A.htm[/url] [/QUOTE]
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