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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
bullet drop and scope leveling
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<blockquote data-quote="goodgrouper" data-source="post: 103282" data-attributes="member: 2852"><p>Meichele,</p><p></p><p>You are exactly correct. Spin drift is a real ballistic principle and is not made up from fairy tales. The military along with countless other ballisticians have noted and described this very thing. The only way you could have a bullet not drift itself over is if you built a rifle range in a vacuum!</p><p></p><p>It is funny how people like to debate known facts about well established ballistic principles. This isn't anything new, it is ballistics 101.</p><p></p><p>The reason why some folks may not notice it is because it is <font color="red"> different in magnitude for every rifle.</font> SOme show more than others, but THEY ALL HAVE SOME!</p><p></p><p>To quote from R. Rinker in his book:</p><p>"There is no practical method of calculating drift from factors such as velocity, range, etc. Various bullet characteristics that cannot accurately be predicted are involved. Consequently, a direct measurement during testing is the only certain method for determining the drift. This evaluation is common with military ammo, but is not usually done with sporting cartridges and bullets."</p><p>pg 105</p><p></p><p></p><p></p><p>As for the distance the military found the 30-06 to drift, it was 13" at 1000 yards and less at closer distances. In other words, it still was evident at 800 yards and so forth. </p><p>Rinker states:</p><p></p><p>"For ranges below 1000 yards, it is suitable to use the approximate relationship that the drift is proportional to the square of the time of flight, or to the third power of the range. For example, at 500 yards the drift will be approx. 1/8 that at 1k or 1 1/2 inches. At 300 yards it will be about 1/30 that at 1000 yards or about 3/8 inches. While it is excessive at ranges well over 1000 yards, it is small enough to be of no concern at <em>normal</em> ranges. The Springfield .30-06 rifle's rear sight apertureis mounted on a slide that is inclined and also slanted to the left. As the sight is raised higher for longer range shooting, the sight also moves a slight amount to the left to compensate for drift."</p><p>Pg 105 bottom paragraph</p><p></p><p></p><p>So you can see, gyroscopic drift effects every bullet every shot and at every range. You simply zero your scope for drop as well as windage at the given range you intend to shoot and that is why it sometimes goes unnoticed.</p><p></p><p>Given that the poster's scope was leveled properly, this phenomenon is very suspect of the amount of drift he is seeing.</p></blockquote><p></p>
[QUOTE="goodgrouper, post: 103282, member: 2852"] Meichele, You are exactly correct. Spin drift is a real ballistic principle and is not made up from fairy tales. The military along with countless other ballisticians have noted and described this very thing. The only way you could have a bullet not drift itself over is if you built a rifle range in a vacuum! It is funny how people like to debate known facts about well established ballistic principles. This isn't anything new, it is ballistics 101. The reason why some folks may not notice it is because it is <font color="red"> different in magnitude for every rifle.</font> SOme show more than others, but THEY ALL HAVE SOME! To quote from R. Rinker in his book: "There is no practical method of calculating drift from factors such as velocity, range, etc. Various bullet characteristics that cannot accurately be predicted are involved. Consequently, a direct measurement during testing is the only certain method for determining the drift. This evaluation is common with military ammo, but is not usually done with sporting cartridges and bullets." pg 105 As for the distance the military found the 30-06 to drift, it was 13" at 1000 yards and less at closer distances. In other words, it still was evident at 800 yards and so forth. Rinker states: "For ranges below 1000 yards, it is suitable to use the approximate relationship that the drift is proportional to the square of the time of flight, or to the third power of the range. For example, at 500 yards the drift will be approx. 1/8 that at 1k or 1 1/2 inches. At 300 yards it will be about 1/30 that at 1000 yards or about 3/8 inches. While it is excessive at ranges well over 1000 yards, it is small enough to be of no concern at [i]normal[/i] ranges. The Springfield .30-06 rifle's rear sight apertureis mounted on a slide that is inclined and also slanted to the left. As the sight is raised higher for longer range shooting, the sight also moves a slight amount to the left to compensate for drift." Pg 105 bottom paragraph So you can see, gyroscopic drift effects every bullet every shot and at every range. You simply zero your scope for drop as well as windage at the given range you intend to shoot and that is why it sometimes goes unnoticed. Given that the poster's scope was leveled properly, this phenomenon is very suspect of the amount of drift he is seeing. [/QUOTE]
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