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Help calculating MOA/Hold-Over on this Reticle

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 08:41
garyalarson View Drop Down
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How do I calculate MOA/Holdover for this reticle? It's for the Vortex Crossfire II 6-18x44 V-brite. (Second focal plane). I abbsolutely love it but will be heading out to do some long range shooting at the end of the month and would like to know how to create a hold-over chart. (Because of the break in lines and no MILs, I know it won't be exact. But I'm just looking to put together a chart that will help me not miss so much. :)

My Plan: Head to the range with target with 1in squares. At 100 yards I would zoom all the way in and position the rifle so that the center of the dot is fixed on the left side of a square. Carefully count how many inches to the edge of the thin line (see yellow oval #1.)  Do the same for where the thicker line starts (#2), and end of line (#3).
 
Questions/Assumptions: If there is 3.5 inches to #1 line at 100 yards, would extrapolate equally every 100 yards? (7 inches at 200 yards, 10.5 inches at 300 yards, etc. etc, up to 35 inches at 1,000?)
 
I know this isn't the ideal reticle for this type of hold overs, but trying to make due and would like ideas/feedback on my approach.
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 09:29
Sparky View Drop Down
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Here are the reticle subtensions. And I am guessing this is the reticle you have.

http://www.vortexoptics.com/uploads/sub_cf2_s_6-18x44_bdc.jpg

If not here is the scope and just click on the reticle you have and then the subtension detail.

http://www.vortexoptics.com/product/crossfire-II-6-18x44-ao-with-dead-hold-bdc-moa-reticle/reticle
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 09:41
garyalarson View Drop Down
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Mine is the V-brite reticle, not the BDC.
 
If you look at this graphic, or the one above, you can see my dillema. (I just edited the one above with yellow circle and blue lines to illustrate my strategy, but the red dot and black lines are accurate in how it looks.)


Edited by garyalarson - August/06/2013 at 10:30
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 13:57
Rancid Coolaid View Drop Down
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Assuming you always measure with on the same magnification, your process works.

Be aware that if you are on another magnification, your numbers will be wrong, but it all looks the same in SFP.
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I would try and look at it as MOA rather than inches.  It wouldn't be the most precise way to do it as every error is going to be multiplied the further you go out.  However, in theory this sounds plausible just not practical. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 14:03
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Run ballistics once you find out how many MOA it is down, and I'm sure you could get close to seeing how far the top of the skinny post will get you, so you can at least be on paper.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 14:05
garyalarson View Drop Down
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Originally posted by Rancid Coolaid Rancid Coolaid wrote:

Assuming you always measure with on the same magnification, your process works.

Be aware that if you are on another magnification, your numbers will be wrong, but it all looks the same in SFP.
 
Awesome! That is a classic example of doing McGuyver-Style trouble shooting. (2 pieces of licorice + 1 bottle acrylic fingernail polish + 52.1oz. warmed goat milk = Guided Missle)
I will definately use MOA vs. inches in my chart. Thanks everyone.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 15:39
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Originally posted by Rancid Coolaid Rancid Coolaid wrote:

Assuming you always measure with on the same magnification, your process works.

But isn't the 3.5" at 100 yards ONLY valid at the highest power?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 15:53
garyalarson View Drop Down
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Originally posted by tpcollins tpcollins wrote:

Originally posted by Rancid Coolaid Rancid Coolaid wrote:

Assuming you always measure with on the same magnification, your process works.

But isn't the 3.5" at 100 yards ONLY valid at the highest power?
 
Yes. Once I mess with that dial, all bets are off.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 17:54
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I see your dilemma also, as there is no subtension info for those values in the catalog. Measuring at 50 +/or 100 is the way to go to figure it out. I have done this many times with other reticles, especially simple plex in scope's whose companies don't advertise those values. If the value of "1" in your optic turned out to be 2", then the edge of the dot would be a .1 subtension value the same as a mil-dot type of reticle works. I always measure every stadia point in all of my reticles to help with rangefinding and trajectories.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 18:44
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FOR use with (Minute of Angle) MOA RETICLES

MOA Rangefinding Table in YARDS

Height of target in inches divided by MOA times 95.5 = distance in yds

moa

9in 12 16 18 20 22 24 28 32 36

1 860yds 1146 1528 1719 1910 2101 2292 2674 3056 3438

2 430 573 764 860 955 1051 1146 1337 1528 1719

3 287 382 509 573 637 700 764 891 1019 1146

4 215 287 382 430 478 525 573 669 764 860

5 171 229 306 344 382

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 18:47
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MIL/MOA/S-MOA Distance Equations

Below are the distance equations for various combinations of reticles, units of height, and units of distance to the target. 

Height of Target (yards) x 1000 = Distance to Target (yards)

mils

Height of Target (inches) x 27.78 = Distance to Target (yards)

mils

Height of Target (inches) x 25.4 = Distance to Target (meters)

mils

Height of Target (meters) x 1000 = Distance to Target (meters)

mils

Height of Target (cm) x 10 = Distance to Target (meters)

mils

Height of Target (inches) x 95.5 = Distance to Target (yards)

moa

Height of Target (inches) x 87.32 = Distance to Target (meters)

moa

Height of Target (meters) x 3437.75 = Distance to Target (meters)

moa

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 20:09
garyalarson View Drop Down
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Thanks! I think we will be shooting all know distances but was looking more for windage holdover. "Spotter says hold left 2 minutes for wind." On my reticle I'm like uhhhh. But if I can create this bootleg chart I will be close on my holdovers. I hope ;)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/06/2013 at 20:12
Rancid Coolaid View Drop Down
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Check your fire!

This works at ANY power, so long as you always range at the SAME power. With a 24X, I wouldn't use the max as lots of ranging will be with things that might not fit the reticle well.

If you always range at 12X, it still works. Just always be sure you are at exactly 12X. My only SFP is a Hensoldt 3-12 and I can range dead nuts at 6X or half the corrected value for ranging at 12X..

Another - far more complicated - factor. If you range at 24X, at exactly 12X (exactly half) your numbers will be off by a constant factor of 2. At 6X (exactly half of half) they will be off by a factor of exactly 4. It's allot I math, which is why I prefer FFP for most applications.

Carry on.
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