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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: 1125600" data-attributes="member: 5302"><p>Mike, you made some good points. Yes, drift and deflection are two different things that are often intermingled.</p><p></p><p>I think "drift" should be what's caused by the dynamics of the bullet and not that of any external force on it. Spin drift's caused by the gyroscopic stuff bullets have.</p><p></p><p>"Deflection" is caused some external force that moves the bullet. Gravity pulls it down. Wind blows it in all directions, speeds it up, and slows it down; mostly in the horizontal plane. Colder/thicker air slows it down more than warmer/thinner air.</p><p></p><p>If a bullet's dropped 100 yards above ground, it'll fall down:</p><p></p><p>* in different orientations depending on its axis angle upon release and probably end up going base first at the last part of its travel. If the wind's blowing, it'll move horizontally with the wind in varying amounts depending on its orientation to the wind direction; less for a given drop distance as it speeds up so its curve will be the reverse of fired bullets that slow down to impact. Its speed will increase until it reaches maximum that may well vary.</p><p></p><p>* in a point down orientation of directed that way and spun fast enough to stabilize it. It'll also deflect horizontally depending on its resistance to the wind's force. Its spin axis will stay aligned with its fall axis until impact.</p><p></p><p>If a bullet's shot horizontally from a barrel properly spin stabilized, it'll:</p><p></p><p>* fly through its trajectory with its long axis parallel to that trajectory until it starts transcending the sonic barrier; depending on its imbalance, it'll take off in some direction other than a normal trajectory and it'll slow down faster. A cross wind will move it horizontally and its spin axis will follow the combined fall due to gravity and deflection from wind forces. If the wind stops while it's angling off to the side of the line of sight, the bullet will maintain that direction and fall normal rates until some other external force moves it. </p><p></p><p>* There'll be a small amount of spin drift in the direction of the rifling. </p><p></p><p>* For a right hand twist, the bullet will tend to deflect lower towards 4 o'clock with a wind from the left, higher towards 10 o'clock with a wind from the right. It's much more noticeable with bullets going near the speed of sound.</p><p></p><p>======================</p><p></p><p>Any unbalance the bullet has upon exit from the muzzle will deflect it from the bore axis in the direction of the heavy side. It'll wobble/nutate enough to increase drag and strike lower on target than these leaving at the same muzzle velocity but are perfectly balanced.</p><p></p><p>Anytime the bullet's long axis is not parallel to its trajectory, it'll have more drag</p></blockquote><p></p>
[QUOTE="Bart B, post: 1125600, member: 5302"] Mike, you made some good points. Yes, drift and deflection are two different things that are often intermingled. I think "drift" should be what's caused by the dynamics of the bullet and not that of any external force on it. Spin drift's caused by the gyroscopic stuff bullets have. "Deflection" is caused some external force that moves the bullet. Gravity pulls it down. Wind blows it in all directions, speeds it up, and slows it down; mostly in the horizontal plane. Colder/thicker air slows it down more than warmer/thinner air. If a bullet's dropped 100 yards above ground, it'll fall down: * in different orientations depending on its axis angle upon release and probably end up going base first at the last part of its travel. If the wind's blowing, it'll move horizontally with the wind in varying amounts depending on its orientation to the wind direction; less for a given drop distance as it speeds up so its curve will be the reverse of fired bullets that slow down to impact. Its speed will increase until it reaches maximum that may well vary. * in a point down orientation of directed that way and spun fast enough to stabilize it. It'll also deflect horizontally depending on its resistance to the wind's force. Its spin axis will stay aligned with its fall axis until impact. If a bullet's shot horizontally from a barrel properly spin stabilized, it'll: * fly through its trajectory with its long axis parallel to that trajectory until it starts transcending the sonic barrier; depending on its imbalance, it'll take off in some direction other than a normal trajectory and it'll slow down faster. A cross wind will move it horizontally and its spin axis will follow the combined fall due to gravity and deflection from wind forces. If the wind stops while it's angling off to the side of the line of sight, the bullet will maintain that direction and fall normal rates until some other external force moves it. * There'll be a small amount of spin drift in the direction of the rifling. * For a right hand twist, the bullet will tend to deflect lower towards 4 o'clock with a wind from the left, higher towards 10 o'clock with a wind from the right. It's much more noticeable with bullets going near the speed of sound. ====================== Any unbalance the bullet has upon exit from the muzzle will deflect it from the bore axis in the direction of the heavy side. It'll wobble/nutate enough to increase drag and strike lower on target than these leaving at the same muzzle velocity but are perfectly balanced. Anytime the bullet's long axis is not parallel to its trajectory, it'll have more drag [/QUOTE]
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Wind Drift; First Third vs. Last Third of Target Range
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