# Angle Cosine Indicator ~ Confusion

Discussion in 'Long Range Hunting & Shooting' started by Propdoc03, Sep 12, 2011.

1. ### Propdoc03Well-Known Member

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At the great risk of embarrassing myself, not the first time, I have a question.

So I have the Angle Cosine Indicator ready to bolt on my rig.

I am out in the field and get my cosine reading, say 91.

I range my target at 500 yards.

I simply multiply 500 x .91 which gives me 455 yards.
Correct?

Thanks!
PD

2. ### WildRoseWell-Known Member

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Feb 3, 2011
Pretty much. There's a good in depth article explaining the how comes, why for's etc here.

Angle Shooting

3. ### Propdoc03Well-Known Member

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Re: Angle Cosine Indicator ~ Knights Armament BulletFlight app

Very good, thanks WildRose!

For some reason I was trying to make this more difficult or something. I was thinking I need the angle to put into my Knights Armament BulletFlight app.
I had read up on everything but for some reason it just wasnt clicking.
I may not be fast but I am slow ;-)

Now I just range the big muley below, get my cosine reading, calc it, enter my atmospheric conditions, dial it, pray again, drop it!

Cheers
PD

Last edited: Sep 12, 2011
4. ### C.O. ShooterWell-Known Member

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Jul 20, 2011

ex..

500 yards = 9 MOA
20 degree angle = .94 cosign
.94 cosign x 9 MOA = 8.46 MOA or call it 8.5 MOA

5. ### angus-5024Well-Known Member

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imputing your angel into a ballistics program will give you the best solution. apllying your cosign number to your come-ups will be the next best. your yardage will be the least accurate of the three methods.

6. ### WildRoseWell-Known Member

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Re: Angle Cosine Indicator ~ Knights Armament BulletFlight app

I learned to follow this axiom years ago. KISS

Keep

It

Simple

Stupid.

No need to over complicate it. If you are using a ballistic computer in the field, then just input either the angle or the angle cosine as your program calls for it along with the other data.

Some of us dinosaurs are still stuck on pencil and paper or doing the math in our heads as we go though HA!

7. ### RioHondoHankWell-Known Member

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Oct 10, 2010
I don't believe that this will give near the same result as multiplying the cosine by the yardage since the yardage is a linear function and the moa drop is a geometric function, I may be wrong, but I believe if you try to work the problem the two different ways you will get two different results. Only one of the methods can be correct if they give two different answers.

For example for my 6.5-284 the moa drop at 1000 yds is about 26 moa. 26 x .94 = 24.44. If I multiply 1000 x .94 I get 940 yds which shows up as about 23 moa on my ballistic chart. The results in a 14.4 inch differerence in POI and I will miss that antelope. The divergence gets even worse as you increase the angle.

The correct method is to multiply the yardage by the cosine for corrected yardage and use that yardage to get the moa drop from your chart or program. Of course some programs have a provision to enter the angle or cosine. Ballistic FTE on my iPhone does the whole thing for me automatically since the iphome has the capabilitie to measue angles from level and I have a bracket to mount it to my gun.

8. ### RioHondoHankWell-Known Member

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Actually the most accurate result is to enter the angle in your program since the difference between your line of sight and bore of the barrel also comes into play. This becomes a very complex calculation that would not be easily handled in the field. If you don't have a portable ballistics calculated such as the IPhone and Ballistic FTE you would have to have a whole stack of charts for all the angles.

The following gives some idea how complex it would be. After looking at the formulas I am glad I have an iPhone.

Rifleman's rule - Wikipedia, the free encyclopedia