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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Range finder results at up and down angles.
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<blockquote data-quote="LouBoyd" data-source="post: 410365" data-attributes="member: 9253"><p>Sure, the cosines of + and - any angle are the same, but that's only part of the calculation. There are two "accelerations" on a bullet in flight. The acceleration of gravity is only 1 or 2 percent that of the acceleration (deceleration) from air drag, but it's always present. With any uphill shot a bullets velocity will be a little slower than with a downhill shot. The difference being from the gravitational forward component (forward with respect to the bullets spin axis) on the bullets travel over it's trajectory. As range increases and the angles are greater that difference becomes increasingly important. If the software ignores the sign of the angle it's at least a less complete model than one which includes the gravitational effect. For a detailed explanation see "Modern Exterior Ballistics" by Robert F. McCoy. He was the ballistics researcher at the Aberdeen Proving Grounds who wrote the original McTraj software which most modern ballistics programs are based on. </p><p></p><p>The JBM software handles the gravitational component of up/down shooting correctly. I'm not familiar with the Nightforce software, but if it has no provision to enter the sign of the angle to the target it cannot be correcting for both uphill and downhill gravitational effects.. </p><p></p><p>All ballistics programs are incomplete models. Most software models don't include corrections for such things as spin drift, bullet yaw, precession, wind jump, Coriolis effect, etc but those are usually smaller than the measurement errors in major input parameters, particularly wind. If an under 4 inch calculation error for +/- 30 degree shots at 1000 yards concerns you then don't use the Nightforce software. On the other hand who can estimate downrange wind speed well enough when shooting at 1000 yards to get deflection errors under 4" even if the software is perfect?</p></blockquote><p></p>
[QUOTE="LouBoyd, post: 410365, member: 9253"] Sure, the cosines of + and - any angle are the same, but that's only part of the calculation. There are two "accelerations" on a bullet in flight. The acceleration of gravity is only 1 or 2 percent that of the acceleration (deceleration) from air drag, but it's always present. With any uphill shot a bullets velocity will be a little slower than with a downhill shot. The difference being from the gravitational forward component (forward with respect to the bullets spin axis) on the bullets travel over it's trajectory. As range increases and the angles are greater that difference becomes increasingly important. If the software ignores the sign of the angle it's at least a less complete model than one which includes the gravitational effect. For a detailed explanation see "Modern Exterior Ballistics" by Robert F. McCoy. He was the ballistics researcher at the Aberdeen Proving Grounds who wrote the original McTraj software which most modern ballistics programs are based on. The JBM software handles the gravitational component of up/down shooting correctly. I'm not familiar with the Nightforce software, but if it has no provision to enter the sign of the angle to the target it cannot be correcting for both uphill and downhill gravitational effects.. All ballistics programs are incomplete models. Most software models don't include corrections for such things as spin drift, bullet yaw, precession, wind jump, Coriolis effect, etc but those are usually smaller than the measurement errors in major input parameters, particularly wind. If an under 4 inch calculation error for +/- 30 degree shots at 1000 yards concerns you then don't use the Nightforce software. On the other hand who can estimate downrange wind speed well enough when shooting at 1000 yards to get deflection errors under 4" even if the software is perfect? [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Long Range Scopes and Other Optics
Range finder results at up and down angles.
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