Is it as simple as pulling out my calipers and measuring the distance between scope and bore?
Scope height and how to calculate?
- Thread starter Redick
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No, the scope and barrel are not parallal lines, so the "height" depends on where you measure. I get the scope height for chairgun by zeroing my scope at 30 yards, then counting clicks to get my 10 yard zero. I put whatever number into chairgun it takes to get the clicks needed at 10 yards to match up.
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yes, Scope height is just that, the distance between boreline and scope centerline. Frankly its not critical to get down to the thousandth, or worry about droop, shroud concentricity,and those things, because the ballistics programs just arent that good, and often require a couple variables (scope height and pellet BC) to be fiddled with to make the curve fit.
I usually just measure the scope mount split to the perceived middle of the barrel or shroud and call it good. I used to precisiely measure barrel dia, and scope bell dia, and the distance between barrel top and scope bell bottom, then get the radius of each, and figure the height between the centers .... but eventually found it was a thankless task to the ballistic programs I tried. I also felt the distance near the turrets was maybe better vs the bell, but it doesn't seem to be.
I usually just measure the scope mount split to the perceived middle of the barrel or shroud and call it good. I used to precisiely measure barrel dia, and scope bell dia, and the distance between barrel top and scope bell bottom, then get the radius of each, and figure the height between the centers .... but eventually found it was a thankless task to the ballistic programs I tried. I also felt the distance near the turrets was maybe better vs the bell, but it doesn't seem to be.
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http://Airgunaccuracy.wordpress.com/chairgun-and-scope-height/
This is the best way to determine scope height.
This is the best way to determine scope height.
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Whether that is the "best way" will depend on the program being used.
One problem with taking the Line-Of-Sight height at the muzzle, is that the height changes slightly whenever you click or use holdover stadia.
I find ChairGun to be a very useful program. Though, of the few versions of ChairGun that I have used, none of them appear to take everything into account with regards to the scope.
I still use ChairGun sometimes, but I use my own spreadsheet to generate my final dope. My spreadsheet takes into account the correct position of the scope both horizontally and vertically. Scope height should be measured at the second focal plane, which ideally should coincide with the erector tube gimbal. That is where all distances are measured relative to clicks, and the point that LOS height does not change when you click the scope.
Though click angles begin at the gimbal, projectile drop is taken from the muzzle. They are rarely the same point and that fact is taken into account in my spreadsheet.
Some versions of ChairGun do not allow you to enter the sight base. So measuring the LOS height at the muzzle makes sense – until you need to click or use holdover. My current version of Chairgun does have the sight base entry, and it suggests taking the sight base measurement from the turrets to the muzzle. I guess because that's easy to do and close enough. That gets clicks closer to where they should be, especially for close shots. But then it says to still take the LOS height at the muzzle. ??? So it's still going to get an LOS error when you click any significant amount. Now the user will need to recalculate the scope height every time they make any significant clicks to the scope. ChairGun should take the height at the sight base and then extrapolate out to the muzzle rather than make the user do it manually. I don't know if ChairGun actually does that step in the program. Maybe it extrapolates back from the muzzle? Not knowing for sure, I take the scope height at the scope, not the muzzle, as my spreadsheet does that method correctly.
If a lot of your shooting is inside the trajectory apex, these small errors can make a noticeable difference. But it does not matter all that much for long shots.
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Get a caliper reading of the OD of the objective end of the scope, divide by 2. Write that # down. Get a caliper measurement of the space between the bottom of the scope objective and the top of the barrel. DO NOT divide by 2. Write that # down. Get a caliper reading of the OD of the barrel just in front of the the scope objective and divide that # by 2. Write that # down. Add the three numbers you wrote down. That is the reading from the bore to the center of the scope.
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I seen it on here measure barrel od divide by 2, measure objective lens devide by 2 measure bottom of objective to top of barrel, add all 3 numbers together.
OOPs what cmatera said
OOPs what cmatera said
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Scotchmo,
you have an uncanny ability to make us look at a problem from a different angle.
The forums are great when there's people like you.
So, help me out to change my erroneous ways as far as scope height goes....
I used to use the measure-at-the-muzzle method described in the link above.
And I use Strelok Pro for my ballistics.
And I do click a lot. On variable FFP scopes. And shoot between 10 and 100 yards, all over the place...
➔ So, where would you recommend to measure the scope height in my case?
You say: "Scope height should be measured at the second focal plane, which ideally should coincide with the erector tube gimbal. That is where all distances are measured relative to clicks, and the point that LOS height does not change when you click the scope."
I don't know how to interpret that sentence — or where the parts in italics are located on an FFP scope....! 
THANKS!!
Matthias
you have an uncanny ability to make us look at a problem from a different angle.
The forums are great when there's people like you.
So, help me out to change my erroneous ways as far as scope height goes....
I used to use the measure-at-the-muzzle method described in the link above.And I use Strelok Pro for my ballistics.And I do click a lot. On variable FFP scopes. And shoot between 10 and 100 yards, all over the place... ➔ So, where would you recommend to measure the scope height in my case? You say: "Scope height should be measured at the second focal plane, which ideally should coincide with the erector tube gimbal. That is where all distances are measured relative to clicks, and the point that LOS height does not change when you click the scope."
I don't know how to interpret that sentence — or where the parts in italics are located on an FFP scope....! THANKS!!
Matthias
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Many of my advertised 1/8 click scopes are really 1/7. In addition to scope height, true click value is important entry data for any ballistic program. Data out is only as good as data in.
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"Many of my advertised 1/8 click scopes are really 1/7...."
Though possible, that is unlikely. The 1/7 is more likely to be a measurement error. There are two types of 1/8 click scopes. 1/8" and 1/8MOA. They are not the same thing.
Some people use the distance from the muzzle to target when figuring click values. That is not correct. Distances should be taken from the scope (the erector tube gimbal to be exact). That error can translate to a significant click error, especially at close targets. And then if your scope has 1/8MOA clicks, the two errors combine to end up giving 1/7" clicks at 10 yards from the muzzle.
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Scotchmo,
...
You say: "Scope height should be measured at the second focal plane, which ideally should coincide with the erector tube gimbal. That is where all distances are measured relative to clicks, and the point that LOS height does not change when you click the scope."
THANKS!!
Matthias
If your scope rail has any MOA compensation built in, take it from the center of the magnification ring, or transition of the ocular tube to main tube. That is the approximate location of the gimbal.
If you have a straight scope rail, you can measure the height anywhere along the scope tube or objective. But always take your distance measurements from the gimbal. That applies regardless of whether you are using stadia marks or clicks at that distances.
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HI I want to give my was of measuring scope height and also tell you what being off does in accuracy ,and not for just chair gun but for your shot or a 3rd party ballistics program like Applied Ballistics or Streloc pro , and Long range shooting and how I do it , it takes under 15 seconds to measure , get a 6 inch ruler and measure center of scope where you look threw it , then measure in middle of barrel ,
Now you can measure both circumferences but it does not matter to be .001 , this is the least input for long distance shooting , also Most ballistic programs default on 1.5 inches as above line ,
OK now most guns with 34 mm scopes are in the can be about 2.25 to 2.5 inches so it must be changed .
OK now for error of this input , If you shoot 1000 yards 2 inches and it was actually 2.1 inches you would be off by 3/4 of 1 inch at poi or .750 in or 19mm
ok now if you are off by .2 of an inch like you enter 2.1 and it is 2.3 the difference is less then 1 click on a .25moa at 1000 yards
so as for close ranges do the math it does not equate to much to make it too complicated ,
so yes all inputs very important but dont go over board on this like with velocity or angle or environments which if off a small amount at 100 yards can be a miss by 2 feet or more
PS center cut is same as me I am saying do it with 1 measurement he is saying average out at other end , end result is same
LOU
Now you can measure both circumferences but it does not matter to be .001 , this is the least input for long distance shooting , also Most ballistic programs default on 1.5 inches as above line ,
OK now most guns with 34 mm scopes are in the can be about 2.25 to 2.5 inches so it must be changed .
OK now for error of this input , If you shoot 1000 yards 2 inches and it was actually 2.1 inches you would be off by 3/4 of 1 inch at poi or .750 in or 19mm
ok now if you are off by .2 of an inch like you enter 2.1 and it is 2.3 the difference is less then 1 click on a .25moa at 1000 yards
so as for close ranges do the math it does not equate to much to make it too complicated ,
so yes all inputs very important but dont go over board on this like with velocity or angle or environments which if off a small amount at 100 yards can be a miss by 2 feet or more
PS center cut is same as me I am saying do it with 1 measurement he is saying average out at other end , end result is same
LOU
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agree completely.
It is like choosing which distance to zero your scope at: choose one which you will most often shoot at.
Using chairgun and other ballistic calculator, set the zero distance, and play around with the scope height input to see how much it actually affect the resulting POI
That would give you a good indication of how accurate you need to measure each parameter
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There is nothing that substitutes the addition of proper testing with the use of actual poi data as the final follow up for confirmation. Bill
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