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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
A tale of two chrony's
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<blockquote data-quote="Pdvdh" data-source="post: 345018" data-attributes="member: 4191"><p>I sent an e-mail to CED last week and asked them if they're newest model chrony could be used with a larger skyscreen spacing. They told me no, only designed for the 18" spacing. They said a company in Germany tested the unit and determined that there was no benefit to a larger spacing. The 18" spacing was providing just as accurate readings as longer spacings were. </p><p></p><p>Regardless, I agree with Lou Boyd. If conditions are perfect and everything is working properly, their test results and conclusions 'could' largely be true. But their hired independent test firm probably ran the tests with the IR lighting in use and eliminated all other common sources of influence deterimental to chronograph performance that could commonly occur in field use without IR lighting. Greater skyscreen spacing should help reduce the percent of error relative to lesser skyscreen spacings. Even though CED said their instrument can't be reset to calculate velocity at greater skyscreen spacing, I'm sure one could increase the spacing anyhow by 2x, 4x, or 6x, and then it would be necessary to increase recorded velocities by 2x, 4x, & 6X, respectively. </p><p></p><p>I've said it several times in other threads. Until you record your bullet velocity over two chronographs set up in series so that you receive two recorded velocities for each bullet fired, you really have no way of determining if you're getting good data or bad data. Your eyes will then be opened and you'll be able to identify good data when you see good agreement between the differences in the velocity recorded by the two chronos, and to disregard bad data when the delta in the recorded velocity is outside normal delta for your setup. </p><p></p><p>You still won't know which chrony is providing the most accurate, absolute velocity. But at least you'll be able to identify and use good recorded velocity data, consistent with delta in velocity from your units, and have a solid basis trusting those data. Which is enough to ensure that the data <strong>can be</strong> used to determine accurate ES, SD, and BCs (if you so choose to determine your bullet BC by two recorded velocities over a known range).</p><p></p><p>You collect chronograph data over one chronograph and you're shooting in the dark. Shoot over dual chronos in tandem, and you can identify and discard bad sets of velocity data. You still generally can't absolutely know or prove which chrono is acting up, but you can at least ID and disregard suspect (bad) recorded sets of velocity and by doing so, the data that you do use to reach conclusions can lead to valid conclusions. Ken Oehler certainly recognized this - thus as shooters became more demanding they marketed their Model 35 with the proof channel. If I'd known then what I know now, I'd have purchased one or two of those when they hit the stands.</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 345018, member: 4191"] I sent an e-mail to CED last week and asked them if they're newest model chrony could be used with a larger skyscreen spacing. They told me no, only designed for the 18" spacing. They said a company in Germany tested the unit and determined that there was no benefit to a larger spacing. The 18" spacing was providing just as accurate readings as longer spacings were. Regardless, I agree with Lou Boyd. If conditions are perfect and everything is working properly, their test results and conclusions 'could' largely be true. But their hired independent test firm probably ran the tests with the IR lighting in use and eliminated all other common sources of influence deterimental to chronograph performance that could commonly occur in field use without IR lighting. Greater skyscreen spacing should help reduce the percent of error relative to lesser skyscreen spacings. Even though CED said their instrument can't be reset to calculate velocity at greater skyscreen spacing, I'm sure one could increase the spacing anyhow by 2x, 4x, or 6x, and then it would be necessary to increase recorded velocities by 2x, 4x, & 6X, respectively. I've said it several times in other threads. Until you record your bullet velocity over two chronographs set up in series so that you receive two recorded velocities for each bullet fired, you really have no way of determining if you're getting good data or bad data. Your eyes will then be opened and you'll be able to identify good data when you see good agreement between the differences in the velocity recorded by the two chronos, and to disregard bad data when the delta in the recorded velocity is outside normal delta for your setup. You still won't know which chrony is providing the most accurate, absolute velocity. But at least you'll be able to identify and use good recorded velocity data, consistent with delta in velocity from your units, and have a solid basis trusting those data. Which is enough to ensure that the data [B]can be[/B] used to determine accurate ES, SD, and BCs (if you so choose to determine your bullet BC by two recorded velocities over a known range). You collect chronograph data over one chronograph and you're shooting in the dark. Shoot over dual chronos in tandem, and you can identify and discard bad sets of velocity data. You still generally can't absolutely know or prove which chrono is acting up, but you can at least ID and disregard suspect (bad) recorded sets of velocity and by doing so, the data that you do use to reach conclusions can lead to valid conclusions. Ken Oehler certainly recognized this - thus as shooters became more demanding they marketed their Model 35 with the proof channel. If I'd known then what I know now, I'd have purchased one or two of those when they hit the stands. [/QUOTE]
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A tale of two chrony's
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