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Drastic BC change from 800 t0 900 yds??

 
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  #1  
Old 09-09-2009, 10:29 PM
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Drastic BC change from 800 t0 900 yds??

I've been shooting some 140 bergers at 3130' in my 6.5 Sherman from a 300 yd. zero out to 900 yds. Everything is within a click using JBM's trajectory charts out to 800 yds and then suddenly at 900 yds I need 5 extra clicks to be on? What the heck is going on there?? Is it possible that the bc falls off that much at a certain velocity?? I don't think so. The velocity at that range would just be dropping under 2000'. What say you guys?...Rich
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Old 09-09-2009, 11:20 PM
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Re: Drastic BC change from 800 t0 900 yds??

Out of curiousity, what is the chart info. at 700 & 800 yards? Speed, drop, etc.

Thanks,

iSnipe
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  #3  
Old 09-10-2009, 02:19 AM
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Re: Drastic BC change from 800 t0 900 yds??

How much are you off (in a real unit other than 'clicks')? ;)


Assuming this is consistent and repeatable across multiple sessions, one rational explanation is that your scope's tracking could be off in that range of adjustment --
might want to verify your scope's click values in and around the "click range" where you're seeing the weirdness...

One experiment you could do: If you have a reticle that you can use for hold-offs, you could dial up into the range where everything is "working", then use the reticle to hold off for the rest of your elevation --

So just for example (example values here) -- if your verified 800 yard dope is 18 MOA and your 900 yard calculation says 22.25 MOA -- you could dial 18.25 MOA and then use your reticle to hold "up" another 4 MOA. If that is "on", but when you dial up to 22.25 MOA you are off, you know something is up with the scope.

Make sure you're at the power your reticle is calibrated at if the reticle is SFP (and preferably, you'd want to confirm your reticle's calibration).
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Old 09-10-2009, 10:49 AM
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Re: Drastic BC change from 800 t0 900 yds??

Are you using the "litz" bullet in the drop down or the the standard? If your not using the "litz" option try it out. It should match better if it's available for your bullet.
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Last edited by jmason; 09-10-2009 at 02:25 PM.
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Old 09-10-2009, 11:48 AM
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Re: Drastic BC change from 800 t0 900 yds??

If your using the g1 bc its calculated at .640 and berger is now claiming .612. At that distance it may start seeing that diff.

Last edited by learning; 09-10-2009 at 01:13 PM.
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  #6  
Old 09-10-2009, 01:14 PM
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Re: Drastic BC change from 800 t0 900 yds??

That might be half your problem the other half could be a drop in bc I guess?
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  #7  
Old 09-10-2009, 02:21 PM
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Re: Drastic BC change from 800 t0 900 yds??

What drag model are you using?

Sounds like you need to use a different drag function and BC all together.
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