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What defines 'Sight Height'?

 
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  #1  
Old 07-27-2009, 05:21 PM
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What defines 'Sight Height'?

I'm using a 20 MOA base. When the ballistics programs ask for sight height, are they asking for the distance between the bore and a) front b)midpoint or c) back of scope's centerline? Does it matter that much or is 1.5", which seems to be the standard, fine to use?
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Old 07-27-2009, 05:24 PM
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Re: What defines 'Sight Height'?

Just measure from the midpoint of the bore (action) to the midpoint of the scope body (objective lens). I simply open the bolt until it is even with the ocular lens, then I use a caliper to measure from the middle of the bolt to the middle of the lens. Do it a couple times until you are comfortable with the number.

Don't just use the "standard" 1.5" unless yours measures 1.5"

AJ
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Last edited by AJ Peacock; 07-28-2009 at 03:04 AM. Reason: changed objective to ocular (typo)
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Old 07-27-2009, 06:40 PM
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Re: What defines 'Sight Height'?

Some where I saw to measure the OD of your objective and the OD of the barrel add together divide by two, measure the distance between the objective and the barrel and add to the sum of previous measurement and you have the exact center to center.
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Old 07-27-2009, 09:29 PM
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Re: What defines 'Sight Height'?

Quote:
Originally Posted by bigngreen View Post
Some where I saw to measure the OD of your objective and the OD of the barrel add together divide by two, measure the distance between the objective and the barrel and add to the sum of previous measurement and you have the exact center to center.
my thoughts also, or you could get your rings & base dimensions from the manufacturer site and use the scope tube centerline as a reference, then you can get a dim to top of receiver.. just that the bore centerline /barrel profile could be tricky ..
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Old 07-27-2009, 10:43 PM
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Re: What defines 'Sight Height'?

If the scope is on a 20 MOA base, there is a substantial difference between the objective, midpoint, and ocular lens and the rifle bore. Where do you suppose I should take the measurement from?
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Old 07-28-2009, 03:02 AM
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Re: What defines 'Sight Height'?

Quote:
Originally Posted by sdowney View Post
If the scope is on a 20 MOA base, there is a substantial difference between the objective, midpoint, and ocular lens and the rifle bore. Where do you suppose I should take the measurement from?

I have 2 rifles with angled bases, one is 20moa, the other is 40moa. I measured from the center of the ocular to the center of the bolt on both of them and have had no problem with the drops matching the data from JBM & Exbal.

According to my calculations, there shouldn't be much difference between the front and the back with a 20moa base.

1 moa at 100yds (300') = 1.0472"

For a scope that is 1' long and 20moa base, there should only be approx .06981333" difference front to back.

20*1.0472/300 = .069813333" (inches subtension/ft for 20moa base)

You can measure the back and know you are within .1" of whichever number works best with your particular calculator.


AJ
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  #7  
Old 07-28-2009, 10:19 AM
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Re: What defines 'Sight Height'?

Splitting hairs – lay rifle on its side, eyeball with a tape.

Kind of a supersilious anality of an operation you ask me.. plug in 1.5 inches into the balistic calculator and draw your dope out to 1000, then plug in 1.6 , 1.7, 1.8 etc and see the differences, is it really that much? Your going to proof your dope card in the field anyway right? So any discrepancy on the sight height is going to be more then outshined by the results of firing in the field.. just my 2 cent
…. to each their own…
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