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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
You Only Need to Know This If You Shoot Past 700 Yards!
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<blockquote data-quote="Bart B" data-source="post: 765995" data-attributes="member: 5302"><p>Ballistic coefficients are a lot like rifling twist rates; calculating what's best for a bullet at a given velocity involves picking the right stuff to use. There's been all sorts of methods used and some are better than others. </p><p></p><p>My only experience in using calculated bullet drop down range then testing its accuracy has been with Sierra Bullets' software and their bullets. Shooting at 100 yards to get a ballistic zero, then lowering the sights an amount equal to bullet drop plus sight height above bore to get a shooting bore sight for the bullets previously chronographed speed was the first step. 'Twas always interesting that the muzzle axis never aligned 3.5" below the line of sight at 100 yards after doing this; proof the bullet's exit angle was different than the static bore axis angle for a shooting zero at 100. The atmospheric conditions would also be recorded for this zero.</p><p></p><p>On the range at 300, 600 and 1000 yards, come ups from that 100 yard zeros calculated for the atmospheric conditions using actual sight movmemts would be applied. First shot at each range was within 1/2 MOA of point of aim. So, seems Sierra's G1 based calculations were pretty close to reality; at least for the way I used them. </p><p></p><p>Some of Sierra's bullets have 4 or 5 BC's for different velocity bands. My aeronautical engineer nephew told me that airplanes also have different "drag" numbers for different speeds through the air. All of which is not well understood by me as Berger's single G7 BC's per bullet seem to be correct according to them. No doubt the formulas and standards used in the math is different.</p></blockquote><p></p>
[QUOTE="Bart B, post: 765995, member: 5302"] Ballistic coefficients are a lot like rifling twist rates; calculating what's best for a bullet at a given velocity involves picking the right stuff to use. There's been all sorts of methods used and some are better than others. My only experience in using calculated bullet drop down range then testing its accuracy has been with Sierra Bullets' software and their bullets. Shooting at 100 yards to get a ballistic zero, then lowering the sights an amount equal to bullet drop plus sight height above bore to get a shooting bore sight for the bullets previously chronographed speed was the first step. 'Twas always interesting that the muzzle axis never aligned 3.5" below the line of sight at 100 yards after doing this; proof the bullet's exit angle was different than the static bore axis angle for a shooting zero at 100. The atmospheric conditions would also be recorded for this zero. On the range at 300, 600 and 1000 yards, come ups from that 100 yard zeros calculated for the atmospheric conditions using actual sight movmemts would be applied. First shot at each range was within 1/2 MOA of point of aim. So, seems Sierra's G1 based calculations were pretty close to reality; at least for the way I used them. Some of Sierra's bullets have 4 or 5 BC's for different velocity bands. My aeronautical engineer nephew told me that airplanes also have different "drag" numbers for different speeds through the air. All of which is not well understood by me as Berger's single G7 BC's per bullet seem to be correct according to them. No doubt the formulas and standards used in the math is different. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
You Only Need to Know This If You Shoot Past 700 Yards!
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