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Old August 20, 2012, 11:20 AM   #1
Wild Bill Bucks
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Do they all do it?

I've been playing with the "Spot On" site for the Nikon BDC Reticle scopes, and have noticed that the yardage dots change, each time you raise or lower the power from 4 power to 14 power drastically. The system works fine on my ML but I have a 4X12 Weaver on my .308

My question is: Would this be true in a scope that does not have a BDC, such as a variable 4X12 scope, or is this something that only occurs with the BDC scopes?
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Old August 20, 2012, 02:30 PM   #2
Scorch
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1st plane vs 2nd plane scopes. Most scopes are 2nd focal plane scopes, and the reticle does not change as you zoom. This casues issues with BDC scopes. The yardage spots have to shift as you zoom the scope, your field of view is getting smaller and each dot represents fewer yards if they did not shift. Some BDC scopes state they are only accurate at a certain zoom power. A mil-dot scope works well, as do the ranging reticles on Leupold or similar scopes. A 1st plane BDC scope will remain constant in POI throughout the zoom range.

I have limited experience with Nikons, and no experience with their BDC scopes.
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Old August 20, 2012, 07:57 PM   #3
bswiv
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Scorch:

Explain that again.....slower.....smaller words.....?

I kind of got it but the 2nd vrs 1st......does this mean it is on a piece of glass, one of the lenses?

Trying to visualize here.................?
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Old August 21, 2012, 12:54 AM   #4
big al hunter
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Scorch was talking about focal planes. Think of it like this, in second focal plane the reticle appears to be the same size, relative to your eye, no matter what power the scope is set on (the target grows larger,the reticle does not). Therefore the reticle has to shrink or grow with the power change.
On first focal plane scopes the reticle always stays the same relative to the target. This means that the reticle will appear to grow or shrink inside the scope, but it will always cover, ( or subtend ) the same amount of the target (the target and the reticle grow larger). To make the reticle do this differently it must put on different sides of the power adjustment system ( different focal plane ). That is why the BDC changes with the power setting. As stated before most ballistic drop compensation scopes are set to work with most cartridges at max power. This adjustment also allows you to "play" with the power settings and find which one works best with your gun.
And yes wild Bill i believe all Nikon BDC scopes are second focal plane. So yes they will all be different except the main cross hair. Yes your other scopes might have a small change in poi with power adjustment. Shoot a group at each power setting to check your scope. It should not be much if it is even noticeable.
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Last edited by big al hunter; August 21, 2012 at 01:12 AM.
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Old August 21, 2012, 09:05 AM   #5
warbirdlover
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On the BDC scopes you're supposed to only use the circles at the highest power setting after sighting in the crosshairs at the proper range (per their website and your load). It says that in the instructions.
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Old August 21, 2012, 06:11 PM   #6
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If you don't have a BDC scope, sellect one of their Nikoplex scopes, choose the cartridge and bullet. Then fill in the necessary information such as velocity and it will give you the drop figures at your chosen intervals. You can fine tune the program for just about any variable. Great program and it's free.
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Old August 21, 2012, 06:43 PM   #7
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Thank you for the explination........
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Old August 21, 2012, 08:27 PM   #8
SavageSniper
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Yup...that settles it, gonna stay with a mil-dot scope
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Old August 23, 2012, 11:39 PM   #9
big al hunter
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Is that mildot scope first focal plane, or second?...
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