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Up/Downhill corrections

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  #43  
Unread 06-11-2007, 08:33 PM
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Re: Up/Downhill corrections

Any thought to the significance of an angled scope base? I have a 45 MOA base on my "50", which amounts to 0.75 degrees. Scope base and barrel are therefore not parallel.....
Factor of least significance? Gosh I love this stuff..

Scott
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  •   #44  
    Unread 06-11-2007, 10:53 PM
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    Re: Up/Downhill corrections

    [ QUOTE ]
    Any thought to the significance of an angled scope base? I have a 45 MOA base on my "50", which amounts to 0.75 degrees. Scope base and barrel are therefore not parallel.....
    Factor of least significance? Gosh I love this stuff..

    Scott

    [/ QUOTE ]

    Scott,

    That angle is of almost no consequence. Take into account that the LOS and the LOF are never paralell.

    Once you have characterized the trajectory ( Zero Range, MV, BC, DC and environment conditions ) then you have all what is needed. Assuming you have zeroed it at level-fire situation.

    Drop is always measured in a vertical direction regardless of the elevation angle of the trajectory. In other words it does not consider the sights or zero. No matter also if it is measured along either a level range or a slant range, since Drop is a vertical distance as it's measured between the extended bore line ( Line of Fire ) and the point where the bullet passes.
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      #45  
    Unread 06-12-2007, 10:29 AM
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    Re: Up/Downhill corrections

    OK. My dad always told me there was a difference between shooting uphill and shooting downhill and after reading what the pros had to say I always told him BS. (politely, he raised me that way)

    Now maybe I'm taking this to an extreme but I'm a very visual person; I just printed out a random trajectory graph (this one only goes to 400yds)...if I rotate it clockwise ABOUT 45* the bullets in this chart "SHOULD" be dropping straight down (no further effect from gravity) and if I rotate it the same angle counterclockwise...the bullets in this chart are just starting to fall below horizontal (full effect of gravity).

    So, a few questions arise in my little pea brain:
    A. Is this what you guys are already talking about and I'm just starting to catch up?
    B. Is this to extreme to matter to us as shooters?
    C. Am I just oversimplifying a very complex process because my brain is having trouble grasping the whole thing?

    If you print out a drop graph and rotate it you will see what I'm talking about. I understand the horizontal distances are affected by rotating the graph but the effect is still there. I have a feeling there is probably a very easy explanition for what I am seeing, I just don't know what it is. [img]/ubbthreads/images/graemlins/smile.gif[/img]
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      #46  
    Unread 05-13-2008, 11:41 AM
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    is this correct to use then:


    Uphill 800 x .94 = 752

    Downhill 800 / .94 = 851
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      #47  
    Unread 05-13-2008, 01:45 PM
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    As long as the angle up or downhill is the same then the correction is the same...
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      #48  
    Unread 05-13-2008, 02:40 PM
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    Quote:
    Originally Posted by jwp475 View Post
    As long as the angle up or downhill is the same then the correction is the same...

    Not true at longer distances. At longer distances + or - effect of gravity on the bullet is seen.

    Here's an example as per JBM:

    Bullet/BC/MV/Elevation/Temp/Target/Distance/Angle/Drop
    7mm /.87/3250/5000/59/2000/+45 714.2"


    Bullet/BC/MV/Elevation/Temp/Target/Distance/Angle/Drop
    7mm/.87/3250/5000/59/2000/-45 677.2"

    The difference being 36.9 inches. The time of flight is a little different too.
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      #49  
    Unread 05-13-2008, 05:30 PM
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    If you are correct then why doesn't Exball ask if the angle is uphill or downhill?

    I don't know what you used for a zero distance, but with a 100 yard zero Exbal shows a correstion of 685.3 inches and there is no way to imput a + or - degree it simply asks for the degree, I am going with Exbal as its accuracy is proven IMHO
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    Last edited by jwp475; 05-13-2008 at 05:41 PM.
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