How to measure scope height?

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Floridaman2005

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Oct 11, 2024
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I’m attempting to set up Chairgun so I can better understand holdovers and close range shooting. I have an impact m3, warne 20 moa cantilever mount and athlon Midas tac 6-24 scope. How can I get an accurate measurement of scope center to bore center?

I’ve read taking 1/2 the objective lense + 1/2 barrel diameter + distance from barrel to scope but didn’t know if anyone else had similar setup that could let me know roughly what that distance would be. Thanks 👍
 
This gets you real close... Anther place to measure (with a ruler or calipers) is from the centerline of the pellet probe in the breech up to the centerline of the scope tube. With this rear-most measurement you can split the difference of the front measurement from the rear measurement. This will give you three different places along the angled scope to help determine which number is most accurate in Chairgun. With an accurate projectile speed and projectile BC number you can generate a dope chart in Chairgun to use to verify which of the three location numbers are most accurate by shooting at different yardages.
 
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igolfat8 said:
1. Measure OD of barrel or shroud. Divide that dimension by 2.
2. Measure OD of front scope objective. Divide that dimension by 2.
3. Measure gap between top of barrel or shroud to bottom of scope objective.
Add all three and that is scope height.
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of course I missed your thread..... but yes exactly what you said ..... lol
 
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This is per Chairgun....basically as the video describes....

To measure scope height above bore using Chairgun, you need to input the distance between the center of the barrel at the muzzle and the center of your scope's line of sight, essentially measuring from the center of the bore to the center of the optic at the muzzle; this is the critical measurement for accurate ballistic calculations within the software.

Key points about measuring scope height with Chairgun:
  • Centerline measurement:
    The key is to measure from the center of the barrel to the center of the scope's reticle at the muzzle, not just the top of the scope or the rings.

  • Accuracy is key:
    Precise measurement is important as even small variations in scope height can significantly affect bullet trajectory, especially at longer distances.

  • Methods to measure:
    • Direct measurement: Use a caliper or a precise ruler to measure directly from the barrel center to the scope center at the muzzle.

    • Laser method: Some shooters use a laser to project a line from the barrel center to the scope center for a more accurate measurement.

      How to input the measurement in Chairgun:
  • Access the settings:
    Open your Chairgun software and navigate to the relevant settings section where you input your rifle and scope data.
    Enter the value:
    Input the measured distance between the barrel center and the scope center at the muzzle as the "scope height" value.

    mike


 
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manabeknives said:
i wasn't familiar with with this method ..start at the 22minute mark for measuring scope height
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Something that isn’t immediately obvious to me here. Why do you need to cover the lens with aluminum foil? Can’t you see the horizontal line through the scope without that? Wouldn’t “guessing” where the dead center of your lens is and poking a hole throw off your measuring anyways?
 
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Floridaman2005 said:
Something that isn’t immediately obvious to me here. Why do you need to cover the lens with aluminum foil? Can’t you see the horizontal line through the scope without that? Wouldn’t “guessing” where the dead center of your lens is and poking a hole throw off your measuring anyways?
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I have used this method several times and it works, but can be difficult depending on your scope.

Covering the scope is required to help you focus at such a short range (I think it technically changes the depth of field). In his example, his scopes goes down to 10 yards, but the target is actually about 1.5 feet away! You can’t focus at 1.5 feet, so that cover is needed in order to allow you a chance at seeing the aim point.

You can also do it with the measuring method to get close, then test your ranges, and adjust the scope height data point slightly until they match up perfectly. You may have to do this with the foil method as well.
 
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Smok3y said:
I have used this method several times and it works, but can be difficult depending on your scope.

Covering the scope is required to help you focus at such a short range (I think it technically changes the depth of field). In his example, his scopes goes down to 10 yards, but the target is actually about 1.5 feet away! You can’t focus at 1.5 feet, so that cover is needed in order to allow you a chance at seeing the aim point.

You can also do it with the measuring method to get close, then test your ranges, and adjust the scope height data point slightly until they match up perfectly. You may have to do this with the foil method as well.
Click to expand...
Well, I was preparing to do this method and then realized my scope objective and my barrel (500mm m3) end at almost the same point. Was super easy to use a measuring tape to get the height. Next question; is Chairgun the preferred app for airgun ballistics? I realized I couldn’t change the options on the free version. Is there a free calculator that works or do I need to pay for Chairgun?
 
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Pretty simple to line up a square along the center of both rings (as they are in the center of the scope tube) and just measure down to the center of the barrel… but I suppose some folks need a reason to use that 8th grade algebra.

There are a lot of ways to royally screw-up the inputs into Chairgun…. Missing on the scope height by .1” isn’t one of them.
 
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Floridaman2005 said:
Something that isn’t immediately obvious to me here. Why do you need to cover the lens with aluminum foil? Can’t you see the horizontal line through the scope without that? Wouldn’t “guessing” where the dead center of your lens is and poking a hole throw off your measuring anyways?
Click to expand...
By looking through a pinhole at the objective end of the scope, the depth of field is enhanced by orders of magnitude. giving the user a clear sight image at a around 2.5 feet out from the objective. Without the pinhole the sight image would look like a blur. Same principle as a camera lens ( depth of field.)
You may need to throw some lighting onto the target area because you will indeed lose light,, but this will give a very accurate reading on scope height from the intersecting cross hair of the scope to the barrels center bore. Takes about 5 minutes.
 
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I guess that I would have to ask:
If the scope is NOT optically centered, then would the video method be of any actual help?
For instance, if the crosshairs were well beyond optic center, up or down, then it would not be a true measurement, would it?
Kinda like measuring one-half of the scope tube and one-half of the barrel method, at least the SHOULD give a very close measurement.
I have used a flashlight to do the same thing (in a darkened area), shine the light through the scope at a piece of paper to 'extend' the crosshair, mark it with a pencil, then shoot the pellet like the video.

mike
 
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