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# Cosine indicator question

#1
06-07-2008, 09:22 PM
 Silver Member Join Date: Dec 2006 Posts: 214
Cosine indicator question

With out a pocket pc which method of calculating cosine is more accurate, multiplying cosine by MOA or sloped yards?
#2
06-07-2008, 10:16 PM
 Platinum Member Join Date: Feb 2005 Location: USA Posts: 2,599
The same.
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#3
06-08-2008, 01:20 AM
 Silver Member Join Date: Jun 2007 Posts: 213
They actually are not the same -- multiplying the MOA dope by the cosine is the more accurate method of the two.

There's an article on this right here at LRH:

Long Range Hunting - Angle Shooting
#4
06-08-2008, 11:31 AM
 SPONSOR Join Date: Dec 2002 Location: California Posts: 135
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.
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#5
06-08-2008, 01:35 PM
 Gold Member Join Date: Sep 2003 Location: Blighty Posts: 638
Hi Ward,

Hope you are well!

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

Quote:
 Originally Posted by WWB 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:

Quote:
 Originally Posted by Brown Dog 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:

Quote:
 Originally Posted by Brown Dog 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.

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:

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

Last edited by Brown Dog; 06-08-2008 at 01:50 PM..
#6
06-08-2008, 02:07 PM
 Silver Member Join Date: Jun 2007 Posts: 213
Quote:
 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
#7
06-08-2008, 09:25 PM
 Silver Member Join Date: May 2007 Location: Alabama Posts: 157
Quote:
 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

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