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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Velocity swing in 7mm wsm with IMR 7828ssc
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<blockquote data-quote="Jordan Smith" data-source="post: 1166025" data-attributes="member: 44423"><p>The oscillation is actually more of an elliptical shape rather than little circles, with a horizontal component- more like a figure 8. There are two factors in this sine wave oscillation that lead to accuracy, and minimal vertical spread at distance- bullets exiting the muzzle at a node (small groups at short range), and bullets exiting the muzzle as the barrel exits a lower node or enters an upper node (minimizing vertical dispersion at distance). </p><p></p><p>As the barrel oscillates, it reaches as point as it's rising where it briefly stops before it starts coming back down again, which is known as a node. When the bullets are timed so that they exit the muzzle while the barrel is in one of those nodes, the muzzle's motion is minimal, so bullets exit the same way, or very close to the same way, every time. Whether a slower bullet exits the end of the node, or a faster bullet exits at the beginning of the node, they are leaving the muzzle with the barrel in about the same position, and will produce small groups even with large ES muzzle velocities.</p><p></p><p>Minimizing vertical spread is a similar concept, but depends on getting the bullets to exit the muzzle when the barrel is entering an upper node, or exiting a lower node. If you can picture the barrel rising before briefly stopping and coming back down, a bullet traveling down the barrel faster will leave the muzzle sooner while the barrel is pointing lower in its trajectory. A slower bullet will leave the barrel later, when the barrel is pointing higher as it reaches the top of its vertical motion and enters the upper node. So to recap, the faster bullet exits the muzzle when the barrel is pointing lower, and the slower bullet exits when the barrel is pointing higher. This means that the slower bullet is aimed a bit higher than the faster bullet, which neutralizes the difference in trajectory between the faster and slower bullets (the slower bullet is aimed a bit higher, so hits the same POI at long distance as the faster bullet). The same is true as the barrel exits the lower node. This is the theory behind the Audette ladder test. Obviously the lower your SD and ES numbers are, and the closer to the node that the bullets exit the muzzle, the more accurate your load will be at all ranges.</p><p></p><p>Hope that helps clarify the question raised at the end of your post.</p></blockquote><p></p>
[QUOTE="Jordan Smith, post: 1166025, member: 44423"] The oscillation is actually more of an elliptical shape rather than little circles, with a horizontal component- more like a figure 8. There are two factors in this sine wave oscillation that lead to accuracy, and minimal vertical spread at distance- bullets exiting the muzzle at a node (small groups at short range), and bullets exiting the muzzle as the barrel exits a lower node or enters an upper node (minimizing vertical dispersion at distance). As the barrel oscillates, it reaches as point as it's rising where it briefly stops before it starts coming back down again, which is known as a node. When the bullets are timed so that they exit the muzzle while the barrel is in one of those nodes, the muzzle's motion is minimal, so bullets exit the same way, or very close to the same way, every time. Whether a slower bullet exits the end of the node, or a faster bullet exits at the beginning of the node, they are leaving the muzzle with the barrel in about the same position, and will produce small groups even with large ES muzzle velocities. Minimizing vertical spread is a similar concept, but depends on getting the bullets to exit the muzzle when the barrel is entering an upper node, or exiting a lower node. If you can picture the barrel rising before briefly stopping and coming back down, a bullet traveling down the barrel faster will leave the muzzle sooner while the barrel is pointing lower in its trajectory. A slower bullet will leave the barrel later, when the barrel is pointing higher as it reaches the top of its vertical motion and enters the upper node. So to recap, the faster bullet exits the muzzle when the barrel is pointing lower, and the slower bullet exits when the barrel is pointing higher. This means that the slower bullet is aimed a bit higher than the faster bullet, which neutralizes the difference in trajectory between the faster and slower bullets (the slower bullet is aimed a bit higher, so hits the same POI at long distance as the faster bullet). The same is true as the barrel exits the lower node. This is the theory behind the Audette ladder test. Obviously the lower your SD and ES numbers are, and the closer to the node that the bullets exit the muzzle, the more accurate your load will be at all ranges. Hope that helps clarify the question raised at the end of your post. [/QUOTE]
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Velocity swing in 7mm wsm with IMR 7828ssc
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