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Using the Nikon BDC to range find?

 
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  #1  
Old 11-25-2007, 04:16 PM
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Location: South West Montana
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Using the Nikon BDC to range find?

Anyone have a system for using the nikon bdc reticle to range find?

I have a nikon 440(i know should have got the 800) and am looking for ways to range out to 600 yards as that is my effective hunting range given optimum circumstances.

The way I have it figured is that at 10X my scopes max the circles are 2" at 100 yards meaning that they will be 10" at 500 and 20" @1000

Anyone broke this down for ranging diffrent distances?

Jordan
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  #2  
Old 11-25-2007, 04:34 PM
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The BDC is supposed to be used at max power for each scope and the circle is 2" at 100 with that largest power.

You can use a program like Exbal to run the dimensions at different powers. That is also another way to get different ranges (and more accurate POI for the circles) by using different powers.

BH
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Old 11-27-2007, 09:29 AM
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I have a Nikon 3-9 BDC, which I really like, on my Mod 70. Guess I need to go back 'read' the scope book as my Cabela's 800 rangefinder is very disappointing on mule deer at long ranges.
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  #4  
Old 11-27-2007, 08:42 PM
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The book will not help you. For some reason Nikon does not publish the distances from circle to circle. However, you can call the tech line and they will give it to you.

The 3-9 and 4-14s both use 2" circles at max powers. The distance between circles (center to center)at 100 yds and at max power is

1st circle 2"

2nd circle 4.5"

3rd circle 7"

4th circle is 11"

Those are the distances you need with any reticle ballistics program such as Exbal.

BH
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  #5  
Old 11-29-2007, 05:36 PM
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All the reticle subtensions are in the catalog guys, and yes, that reticle has rangefinding written all over it. The problem is the circles aren't really big enuf to range anything to intermediate ranges which is where IMO reticle-rangefinding has the most viability. If u're gonna try and do it way out there, then it will have the correct subtension--1.5 inch per hundred yds. (IPHY)inside diameter, and 2.0 outside.

Now the stadia subtensions between circles would work well, and there's a bunch of stadia points to choose from. How's about a 16" back to brisket buck deer (Leupold std. they use for their RES). Top of last dot to bottom of lower post is 5 IPHY. Now just apply the "modified mil-ranging" formula (MMRF), like this (inches to yds.)--

tgt. size (inches) x range of reticle subtension measurement (usually 100 yds.) / reticle subtension (inches) / quantity of "gap" tgt. occupies = range (yds.).

...looks complicated, super easy to apply. Filling in the variables using the 16" deer, and 5.0 IPHY "subtension unit"--

16 x 100 / 5.0 / 1.0 (deer fits 100% of the gap) = 320 yds.

recognizing that 320 is a constant, we can enter it into the calculator's memory to calculate the rest of the ranging chart as follows--

320 / 0.9 = 350

320/.8=400

320/.7=455

320/.6=530

Now if the deer brackets right in the center of the circle when his brisket is level with the bottom post that would be right at the 4 IPHY subtension. If we divide 4 by 5 (our subtension unit) we get .8 which is the 400 yd. reading noted above. If he fits bottom of circle to lower post that's 3 IPHY. 3/5=.6 ==530 yds. So here's the deer ranging chart --

TLD (top lower dot) to PPT = 320
.9-350
CLD (center lower dot) = 400
.7=455
BLD (bottom...)=530

sweet huh??...assuming u've guessed tgt. size correctly, that is...

How about a pr. dog like Leupold uses for their ranging feature in the VH reticle. They use 7.3" tall for a pr. dog sitting on his haunches on top of his hole, or wherever he might wanna sit, i guess.

x-hair axis to bottom of 1st dot (our new subtension unit)= 3 IPHY, now plug the variables in again--

7.3 x 100 / 3.0 / 1.0 = 245 yds.

243.3 / 0.9 = 270
.8=300
.7=350
.6=400

center of dot= 2 / 3 ==.67 (or about 360 yds.--243/.67=360--can u see it?)

...so here's the range chart for a pr. dog--

X-B1D (bottom 1st dot) = 240
.9=270
.8=300
.7=350
C1D=360
.6=400
etc. to as far as u wanna go.

Once the MMRF is studied and applied i think u'll find it's the quickest, most accurate, and most flexible (can be used with any reticle that has more than 1 stadia point, line, whatever in it, fixed power and variable) reticle rangefinding system there is.

Reticle-rangefinding (and downrange zeroing) is one of the reasons i always get the catalogs from the different optics companies. Many advertise their subtensions, but Nikon is 1 of the best for that.

Last edited by sscoyote; 11-29-2007 at 05:55 PM.
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  #6  
Old 01-21-2010, 07:22 PM
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Join Date: Dec 2008
Posts: 7
Re: Using the Nikon BDC to range find?

Sorry to dig this thread out of the grave, but I wanted to add a link for anyone who is searching:

Monarch 4-16x42SF | MONARCH | RIFLESCOPES
EDIT: Sorry. The link won't work directly. Just click on "Reticles" on the left.

One thing I found that wasn't already in this thread is the distance to where the reticle goes thick. That distance is 15. Also, the thick part is 1inch, and thin part is .25.

Another quick note,.. if you are using the circles as "2 inches", it is 2 to the outside of the circle. The inside is 1.5 inches.

Gonna have to check into that "Exbal" program that was mentioned. Good info in this thread. Got me going in the right direction I think.

Thanks,
Gene
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