The truth about how to find “Sight Height?”

[GungHo]

So most of you have probably stumbled upon “sight height” in your ballistic calculator. And many of you probably think its the distance from the center of the scope to the center of the barrel. However, i stumbled upon an article that refutes that information. This picture summarizes the article.

Chairgun and “Scope Height”

I hear a lot of people complaining about the ballistic software Chairgun not being in line with their real world results. But in my field target rifle and scope combo’s it has improved to bei…

airgunaccuracy.wordpress.com

However, when you look up how to find sight height on youtube(yes i know youtube is not the best place for Information).



So which one is right? Are guns scope intersections with barrel angles the same as in the article about airguns? How does this affect bullet trajectory at long range? Could it be possible that my sight height in my calculator(and yours) of 3.5inches is actually 3.44?

 

[Precision Underground]

Tag. If that is the case I’d love to know because I have about 45moa on my 300 NM mount and I think that would make a big difference.

 

[xdeano]

Ive wondered this also. Ive got an ivey adjustable mount from 0-200moa and the objective lense travels toward the barrel and the ocular lenses travels away from the action.

So is the measurment in the center of the scope at the turrets or at the objective or occular lenses?

 

[LastShot300]

The concept on Chairgun is wrong by a mile or two, it simply makes no sense, wht they suggest is just and adjustment needed for extremely short firing distance. Read the Sierra Manual for a complete explanation and justification from a ballistics perspective.

 

[Ledzep]

Bullet drop at 100yd (typical zero range) is usually about 3". Let's say the center of your scope (the turrets, for example) are 2.5" over the bore. In a perfect world you're accounting, then, for 5.5" over 100yd (3600 inches). Your turrets are probably 2" or so behind your barrel at the breech, and a good guess for barrel length is 24".... So let's gander at how much different your scope over bore would be...

Traditional: 2.5"

This article: 5.5/3600 X 26 = .040" lower, 2.46"

2.5" over bore, 100yd zero 147 ELDM @ 2700 at 1000yd: 8.4 mils on JBM
2.46" over bore, 100yd zero 147 ELDM @ 2700 at 1000yd: 8.4 mils on JBM

At 1500yd,

2.5": 17.0 mils
2.46": 17.0 mils

Fart in the wind...

ETA: Best way I've found to measure scope over bore is to get your calipers to measure the maximum distance from outside of the top of the scope tube to outside of the bottom of the action, then subtract half the diameter of the tube, and half the diameter of the action.

 

[DAVETOOLEY]

Bullet drop at 100yd (typical zero range) is usually about 3". Let's say the center of your scope (the turrets, for example) are 2.5" over the bore. In a perfect world you're accounting, then, for 5.5" over 100yd (3600 inches). Your turrets are probably 2" or so behind your barrel at the breech, and a good guess for barrel length is 24".... So let's gander at how much different your scope over bore would be...

Traditional: 2.5"

This article: 5.5/3600 X 26 = .040" lower, 2.46"

2.5" over bore, 100yd zero 147 ELDM @ 2700 at 1000yd: 8.4 mils on JBM
2.46" over bore, 100yd zero 147 ELDM @ 2700 at 1000yd: 8.4 mils on JBM

At 1500yd,

2.5": 17.0 mils
2.46": 17.0 mils

Fart in the wind...

ETA: Best way I've found to measure scope over bore is to get your calipers to measure the maximum distance from outside of the top of the scope tube to outside of the bottom of the action, then subtract half the diameter of the tube, and half the diameter of the action.

A Tweety bird fart at that.

 

[Geno C.]

I’ve always measured from the center of the action to the center of the erector tube. I haven’t found it to cause any weird anomalies that I couldn’t track down to something else

 

[Deleted member 10043]

I'm sticking with the same ruler Mother Gervasia used to knock some sense into me.

 

[GungHo]

Maybe someone try the website's way of measuring sight height and compare POI at a far distance like 1000 yards. If the poi is closer on one of the results we will know which method is the most accurate.

 

[THEIS]

Maybe someone try the website's way of measuring sight height and compare POI at a far distance like 1000 yards. If the poi is closer on one of the results we will know which method is the most accurate.

Hi,

That is pretty much impossible.
A half mile an hour wind difference creates a larger error margin than any of those 2 sight height comparisons could ever cause.
Would require a sealed and environmentally controlled firing tunnel...and then you would have to ensure your ammunition was a 0 fps muzzle velocity deviation, etc etc.

Sincerely,
Theis

 

[Lowlight]

It's wrong, just look at the image they are bending the line of sight if you follow the line it doesn't work.

Just measure the center of the bore to center scope, these are verifiable and well recognized.

These geniuses did not stumble on a worldwide mistake.

Fake News

 

[LastShot300]

Hi,

That is pretty much impossible.
A half mile an hour wind difference creates a larger error margin than any of those 2 sight height comparisons could ever cause.
Would require a sealed and environmentally controlled firing tunnel...and then you would have to ensure your ammunition was a 0 fps muzzle velocity deviation, etc etc.

Sincerely,
Theis

 

[LastShot300]

It's wrong, just look at the image they are bending the line of sight if you follow the line it doesn't work.

Just measure the center of the bore to center scope, these are verifiable and well recognized.

These geniuses did not stumble on a worldwide mistake.

Fake News

 

[flyer]

I'm not sure they are wrong, but in any standard rifle the muzzle velocity and zero range are high enough and far enough that the barrel and optical center are so close to parallel that the distance from the scope objective to the muzzle doesn't matter.