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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Wind Drift; First Third vs. Last Third of Target Range
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<blockquote data-quote="Bart B" data-source="post: 1125341" data-attributes="member: 5302"><p>Mike, I don't know if Sierra has or not.</p><p></p><p>Some years ago, I talked with their ballistics manager, Martin Hull and either Bob Hayden or Bill McDonald about spin drift. In so many words, they said it's too small and insignificant to put in any ballistic tables. It only comes into play at the longer ranges and is too often masked by subtle cross winds. If corrected for a mean windage zero with a .30-06 shooting a 180-gr. HPMK bullet through 1000 yards, a 1/3 MOA error at most would happen. A little to the left through about 700 yards then about the same amount to the right at 1000. Total drift's about 7 to 8 inches. Easily masked by a subtle cross wind switching back and forth from 1/2 to 1 mph. Nobody I know of can consistently measure all the cross winds' drift in a bullet's trajectory through 1000 yards to correct for within a 1 MOA error.</p><p></p><p>I've tried to use JBM's drift calculator but cannot see spin drift listed in any output column. Used a Sierra 30 caliber 180-gr. HPMK leaving at 2700 fps zeroed at 1000 yards. Unless it's the windage column stating about 7.6 inches.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1125341, member: 5302"] Mike, I don't know if Sierra has or not. Some years ago, I talked with their ballistics manager, Martin Hull and either Bob Hayden or Bill McDonald about spin drift. In so many words, they said it's too small and insignificant to put in any ballistic tables. It only comes into play at the longer ranges and is too often masked by subtle cross winds. If corrected for a mean windage zero with a .30-06 shooting a 180-gr. HPMK bullet through 1000 yards, a 1/3 MOA error at most would happen. A little to the left through about 700 yards then about the same amount to the right at 1000. Total drift's about 7 to 8 inches. Easily masked by a subtle cross wind switching back and forth from 1/2 to 1 mph. Nobody I know of can consistently measure all the cross winds' drift in a bullet's trajectory through 1000 yards to correct for within a 1 MOA error. I've tried to use JBM's drift calculator but cannot see spin drift listed in any output column. Used a Sierra 30 caliber 180-gr. HPMK leaving at 2700 fps zeroed at 1000 yards. Unless it's the windage column stating about 7.6 inches. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Wind Drift; First Third vs. Last Third of Target Range
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