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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Es/sd
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<blockquote data-quote="LouBoyd" data-source="post: 373458" data-attributes="member: 9253"><p>If you measure the ES while shooting at 100 yards certainly the group at 100 yards tells you more about the accuracy of the load at 100 yards. But I'd expect the ES to be a better predictor of what the groups would be like at 1000 yards or more than what the group size at 100 yards tells you. That's assuming that neither the rifle or the chronograph have a severe defect. </p><p> </p><p>Bullet drop is proportional of the square of the time of flight so small velocity variations cause a much larger percentage of the group size at long range (many hundreds of yards) than they do at one or two hundred yards. </p><p></p><p>Wind deflection is proportional to the actual time of fight minus the "vacuum time of flight". (muzzle velocity times distance). Velocity variations do affect wind deflection but only as it directly changes those real and potential times of flight. There is no time squared term related to wind deflection calculation. Generally wind deflection increases over a given distance with decreasing muzzle velocity but there is a dramatic reversal of that trend just below the speed of sound. </p><p></p><p>Wind deflection uncertainty is determined by the shooters ability to judge the wind over the path to the target and to apply that to it's effect on the bullet trajectory. Velocity uncertainty is related the quality and consistency of the loads, and also the condition of the bore from shot to shot. Either wind estimation uncertainty or vertical stringing can be the limiting factor on group size. The accuracy of a marksman (or rifle) at 100 to 200 yards can be nearly unrelated to their accuracy at 1000 plus yards since the dominating errors may be from completely different causes.</p></blockquote><p></p>
[QUOTE="LouBoyd, post: 373458, member: 9253"] If you measure the ES while shooting at 100 yards certainly the group at 100 yards tells you more about the accuracy of the load at 100 yards. But I'd expect the ES to be a better predictor of what the groups would be like at 1000 yards or more than what the group size at 100 yards tells you. That's assuming that neither the rifle or the chronograph have a severe defect. Bullet drop is proportional of the square of the time of flight so small velocity variations cause a much larger percentage of the group size at long range (many hundreds of yards) than they do at one or two hundred yards. Wind deflection is proportional to the actual time of fight minus the "vacuum time of flight". (muzzle velocity times distance). Velocity variations do affect wind deflection but only as it directly changes those real and potential times of flight. There is no time squared term related to wind deflection calculation. Generally wind deflection increases over a given distance with decreasing muzzle velocity but there is a dramatic reversal of that trend just below the speed of sound. Wind deflection uncertainty is determined by the shooters ability to judge the wind over the path to the target and to apply that to it's effect on the bullet trajectory. Velocity uncertainty is related the quality and consistency of the loads, and also the condition of the bore from shot to shot. Either wind estimation uncertainty or vertical stringing can be the limiting factor on group size. The accuracy of a marksman (or rifle) at 100 to 200 yards can be nearly unrelated to their accuracy at 1000 plus yards since the dominating errors may be from completely different causes. [/QUOTE]
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Es/sd
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