Cosine indicator question

Bigcat_hunter

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With out a pocket pc which method of calculating cosine is more accurate, multiplying cosine by MOA or sloped yards?
 
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mattj:

Multiplying the cosine to your MOA or Milliradian hold is more accurate than multiplying the cosine to the sloped distance to target.

This is because you are performing your calculation on a pre-calculated angular method of measurement.
 

Brown Dog

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Hi Ward,

Hope you are well!

I think the 2nd part of your explanation needs a wee tweak :)

Multiplying the cosine to your MOA or Milliradian hold is more accurate than multiplying the cosine to the sloped distance to target.

This is because you are performing your calculation on a pre-calculated angular method of measurement.

The reason for your 1st point being spot-on correct is that applying the cos to comeups (or drop) reflects what is going on ballistically, applying it to the slant (laser) range does not.

I'm going to quote myself from a while back:

Brown Dog said:
The 'base line' [or 'corrected horizontal range' or 'magic physical-law defying range'] method, although used by many is actually the least accurate way of using your cos measurement...because it has absolutely nothing to do with the ballistics of what's going on in inclined fire!

Far more accurate is to multiply the comeup you would have applied for your laser distance by the cos of the angle.
This does reflect what is going on ballistically ...the bullet has the same TOF to a given target regardless of angle of fire...it therefore drops the same amount regardless of angle of fire (it doesn't magically drop less!)

...what changes is your perspective to that drop (and therefore the apparent shape of the trajectory).

Hold a pencil vertically in your hand at arms length (with your arm horizontal); lets say the pencil length represents your bullet drop at 1 arms length.

Now drop your arm to 45deg, but keep the pencil vertical.

The pencil appears shorter, even though it has remained the same length

....ie the drop has remained the same, but less drop is apparent because of your perspective.

How long does it appear to be? multiply it's actual length by the cos of 45deg...just the same as multiplying your laser range comeup by the cos of the angle!

You'll see that Ward at ACI has recently amended his instructions for the ACI to reflect this.

[Thought I should leave that last line in! :) ]



...and as a common-sense check:

Brown Dog said:
Artillerymen receive target locations as grid references.

Grid references alone provide no angle of sight data (ie should the target happen to be on top of a hill or in a valley); and so Gunners are presented immediately with what some riflemen are calling 'true horizontal range'.

But Gunners, if working manually, will use this distance, (plus some trig based on the calculated angle of sight between their location and the target's) to work out the 'slant range' to the target (and then do some other mumbo jumbo too)

....the point being; true long range Jedi :) do (and have done since WW1!) the exact opposite of what the 'corrected horizontal range' riflemen suggest.

So, to restate myself: The reason for your 1st point being spot-on correct is that applying the cos to comeups (or drop) reflects what is going on ballistically, applying it to the slant (laser) range does not.

Meant helpfully! :)

All the best :)

Matt

PS. Thought you might like this pic of a rather technically challenging set of circumstances that faced me earlier this year:

Slide1.jpg


It won't surprise you to learn that we noted a significant vertical wind effect!
 
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mattj

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mattj:

Multiplying the cosine to your MOA or Milliradian hold is more accurate than multiplying the cosine to the sloped distance to target.

That's what I said -- or, at least, that's what I was trying to say :)
 

dmgreene

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the bullet has the same TOF to a given target regardless of angle of fire...it therefore drops the same amount regardless of angle of fire (it doesn't magically drop less!)

Brown Dog are you sure this is correct or am I misunderstanding what you are saying? If you shoot at a target that is at a 90 degree angle up or down then theoretically you don't have any drop from the line of sight do you?

David
 

jwp475

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The only method that is 100% accurate is to run the angle through Exball, IHMO
 

Brown Dog

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Brown Dog are you sure this is correct or am I misunderstanding what you are saying? If you shoot at a target that is at a 90 degree angle up or down then theoretically you don't have any drop from the line of sight do you?

David

Please read the six lines following the piece you quoted.....and you will answer your own question :) .

How tall does the pencil look when held vertically, with your arm vertically above your head?

(worth pointing out that what I'm calling 'drop' is actually the vector resulting from the force/time/acceleration etc of gravity -just easier to illustrate the example by grouping them into 'easy' language -'drop'. Sticking with easy language, for a vertical shot, the drop is straight back down the path of the bullet (in vector terms it will, therefore be a decceleration.)

The only way to reduce the effect of gravity is to get in a space ship :)
 
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Brown Dog

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The only method that is 100% accurate is to run the angle through Exball, IHMO



How do you think Exbal is calculating it??!


I'll eat my hat if it isn't applying the cos of the angle to the bullet's drop. :)
 
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dmgreene

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BD I guess what I'm trying to say is that most of us (or at least I do) consider drop to be the departure of the bullet flight path from the line of sight. I know that gravity will still affect the bullet no matter what, but the steeper the angle the straighter the bullet path will be. I not saying your wrong, I just didn't understand what you were calling drop.

David
 
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Angle Cosine Indicator Calculation method and Night Force Ballistic Targeting softwar

Hello Sir (Brown Dog):

We are still around, aren't we? Have wondered what you have been up to and if you have remained in the UK.

Anyway, I just sent in an article that I wrote regarding Night Force Ballistic Targeting software. It should post soon and I think that you will like it.

All my Best,

-Ward
 

kcebcj

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Great post and really good answers. Information like this is the reason I keep checking this forum. Sure appreciate the people who are in the know for the time you spend answering the complicated questions.

When I was a kid I was taught to pull a little low when shooting up or down hill. I can honestly say that I now know why one does and can figure exactly where to aim.
 
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