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"BDC" and "variable power" question.

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/09/2009 at 09:47
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Optics GrassHopper
Optics GrassHopper


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This is my first post here.  Need a specific question answered that my other gun related forums are perhpas lacking in information.
 
The Bullet Drop Compensator, for the Nikon Coyote, is supposed to make longer distant shots simpler by using the circles as you target out further. However, these scopes are not fixed power, but variable. How can you realistically use a BDC if, when you up the power, the sight picture changes from power to power? For example, if you have your scope set to 5 power, looking at the sight picture will put those circles on a different point than if you up the power to 14.

Anyone have a comment how this is over come, . . . or is there a specific magnification that you have to have it on before the BDC works correctly?

Thanks!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/09/2009 at 09:49
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OT TITAN

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i have a bdc on my team primos (3x9) the bdc only works correctly on 9x, if you want to use it on other powers you have to do the homework and know where it will hit on each circle on each power cause it will change with magnification change.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/09/2009 at 10:22
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Optics GrassHopper
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I thought that to be the case.  So, how would I find out which magnification setting, on a 4.5-14X40 Coyote, will be the one that hits as their diagram (on the Nikon website) shows for a .223?

Thanks!  Smile
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/09/2009 at 10:30
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OT TITAN

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i would assume that it would be 14x but i may be wrong.
the way it looks to me on the nikon page the .223 works like this
http://www.nikonhunting.com/riflescopes-coyote-special-coyote-special-45-14x40.html
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/09/2009 at 10:45
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Optics GrassHopper
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Yes, that is the sight picture I was talking about.  If the 14 power setting is the one that would be correct for the other circles, then that would be excellent.  I could still power down for the 100 yard shots. 
 
I'm considering this scope because of the .223 calculations.  I figure that top of the thick bottom bar would be roughly 450~500 yards.  The .223 isn't a high powered long range projectile, so even the 400 yard circle is about perfect for this round.  The price of the scope is quite good as well.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 09:13
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Optics GrassHopper
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This, from another thread.  Does it sound like it would be same for the BDC?
 
Quote They are all 2nd or rear focal plane reticles. The significance of this is that as the power is changed the measurement (subtension) between stadia change. The best way to understand this is to look at some object at a distance. While keeping the x-hair on some point u should see that as u change the power the stadia change their location on the object. It's actually inversely proportional (power vs. subtension). The system (subtension) is measured in minute of angle (MOA) or inch per hundred yds (IPHY). Ballistics programs calculate bullet drop and drift in MOA and IPHY, so it can be matched to a reticle's subtension. If u go to the Burris website they explain all the systems that can be established for 2nd FP reticles. They have an excellent writeup on that site.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 09:27
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don't confuse ranging with holdover from reticle on second focal plane scopes (sfp). Ranging is linear on the target and radial from the point of measurement and is proportional to the power setting, reticle hold over is a function of the particular ballistic path of the bullet you are using. SFP will raise the point of impact as the power setting is decreased. Swaro,Zeiss, and Leo use this to decrease the power settings on their variables to some number such that the hash marks correspond to certain yardages. So you can use your scope on the highest power, or recalibrate to hit at specific yardages. You will need a ballistic computer package,and your in luck as one of the best is free on the web at JBM.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 12:28
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Optics GrassHopper
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I'm a "scope novice".  Some of what you said is a little hard to understand.  Also, I'm unaware of the website you spoke of, JBM?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/20/2010 at 10:50
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Optics GrassHopper
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I picked up a Matte Black 4.5-14X40 Coyote and am looking forward to putting it on my AR.  Wink
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/21/2010 at 01:32
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/21/2010 at 08:48
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Optics GrassHopper
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Thank you, sir!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/27/2010 at 23:49
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Optics GrassHopper
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Originally posted by 8shots 8shots wrote:

http://www.jbmballistics.com/cgi-bin/jbmcard-5.0.cgi
 
 
 
Wow ... This is a calculator Big Grin
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