# Duplex sight in strategy?



## moabxjeeper (Dec 18, 2012)

I just got done putting a lightweight rifle together and bought a Leupold VX3i 2.5-8x36 with a standard duplex reticle to top it with. I’ve been using a BDC reticle for so long I’ve kind of lost my way with just the duplex crosshairs. I wanted to keep this build as simple as possible and realistically, my goal is to be able to shoot out to 400 yards accurately.

The caliber is 7mm-08 and it’s in a 20” barrel. I’ve run ballistic calculators and if I sight it 3” high at 100 yards, I don’t have to worry about more than 4” of drop until after 300 yards. My question is this - is there a way I can use the top of the bottom post in the reticle as a sort of bullet drop guide, hopefully somewhere near my goal range of 400 yards?


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## DallanC (Jan 13, 2009)

Subtend of a Duplex scope is usually set to 4MOA (check your manual, or on a target at 100 yards). Thats 16" separation at 400 yards. You can play with a ballistics program (ie: PointBlank @ HuntingNut.com) and set the 100 yard sight in height until you get a 16" drop at 400. Look at where the trajectory is about 3-4" low and thats your max PBR (range you can hold and shoot without making elevation adjustments).


You can also use the subtend to range find. A buck is around 18" from shoulder to chest, so bracket it between post and crosshairs. If it fits easily, but buck is beyond 400 yards, if its bigger than the bracket, its closer.


-DallanC


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## nocturnalenemy (Jun 26, 2011)

I was curious as to Dallan's comment because none of my scopes have clean MOA subtensions. Found this on Leupold's website. Your scope is on page 2 and isn't very clean either.

https://cdnp.leupold.com/content/do...ticle_spec_sheet-all.pdf?mtime=20200601072249


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## DallanC (Jan 13, 2009)

nocturnalenemy said:


> I was curious as to Dallan's comment because none of my scopes have clean MOA subtensions. Found this on Leupold's website. Your scope is on page 2 and isn't very clean either.


And to completely muddy the waters, it can also vary depending on zoom setting if you have a First Focal Plane scope vs a Second Focal Plane scope.

Again, set your scope at your normal long range hunting power (9 on a 3x9 etc etc) and aim at a target with 1" lines 100 yards away with the crosshairs centered, now note the tip of the bottom post. That'll tell you your MOA from the center of the crosshairs to the tip of the bottom post. Now multiply that by 4, and you have your rough inches at 400 yards. (1 MOA @ 100 yards = 1.047″ if you want to to get really precise)

Now you can play with trajectories in ballistics software that align with that 400 yard measurement. If you are lucky, you wont be too far above line of sight at any point along the trajectory that would cause a closer range elevation correction. Again, note on the trajectory where its 3-4" low and that is around your max pbr range (the point you have to start making elevation adjustments).

-DallanC


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## DallanC (Jan 13, 2009)

Here's a cool article going about this a slightly different way, showing how to adjust the magnification to match the drop you desire:

http://unionsportsmen.org/riflescope-magic/

The oldie Leupolds used to have yardage markers on the zoom, so you'd zoom in and out to bracket a specific height, then read the number on the bell and you'd know the range. IDK if they still do that with any new models... I havent shopped new leupolds in a very long time.

-DallanC


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## moabxjeeper (Dec 18, 2012)

nocturnalenemy said:


> I was curious as to Dallan's comment because none of my scopes have clean MOA subtensions. Found this on Leupold's website. Your scope is on page 2 and isn't very clean either.


So according to that, the entire "thin opening" is 5.1 MOA at high power. Does that mean I'd divide that in half from the distance from the crosshairs to the top of the post?

Dallan, I like your idea best of lining it up at 100 yards to see how far down it goes. I was just at the range yesterday sighting it in. Wish I would have thought to look.


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## APD (Nov 16, 2008)

if i recall correctly you can get a custom ballistic turret on that scope. 

no matter what you do, make your zero a true zero, not a guess at how far above a known distance you are shooting. it makes everything else easier.


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