Ballistic Calculators - Bullet Drops when Shooting at Inclination Angles...

speedengineer

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Short version - Who likes solving puzzles? Why do Hornady's ballistic calculator results differ from other calculators when shooting at inclination angles? Is this accurate, or not? I live in flatland...I have no way to test empirically.

Hi all. I recently wrote my own point-mass ballistics calculator, and have been comparing its output to several other free ballistic calculators to help validate its accuracy. During these comparisons, I noticed some interesting observations, especially pertaining shooting at inclination angles (either upwards or downwards).
  • When firing horizontally, every ballistic calculator I tried provided effectively the same answer.
  • When firing upwards or downwards, my calculator and all others agree, except Hornady's suggests substantially less vertical correction is required - around 25% less correction for a 30 degree shooting angle. That's an aim point difference of over 20cm at 500 meters.
  • Both Hornady standard 3DOF and their 4DOF provide these results.
  • The difference in calculation results increases with increased inclination angle
  • I have listed the Hornady results excluding the aerodynamic jump and spin drift components, to be consistent with the other calculators. (Aero jump would make the Hornady correction value smaller, anyway...)

Questions...
  • Does anyone have any personal experience validating their rifle's bullet drop at high inclination angles?
  • I am 99% sure I have made no errors entering info into the various calculators. The fact that the wind drift and velocity profile numbers come out spot on suggests no input error. Do you see substantial differences in your calculations between different calculators?
Note - I am not trying to bash Hornady here, I use their products and like their ballistics calculator app, just confused as to the results inconsistency. I'm hoping they know something I don't and their solution is providing the more accurate result. :)

Thanks for any feedback or discussion. I am genuinely interested in understanding what's going on here.
 

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Dog Rocket

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I use AB, Strelok, Trasol, BallisticArc..and Hornady 4DOF.

The first four most commonly agree to within 0.1mil out to 1,200 yards. 4DOF is commonly the outlier when calcs are compared with identical inputs.

I don't know why. I don't use Hornady bullets, so maybe that is it. But as a result, I've all but abandoned it. The user interface is by far the worst of the five anyway.
 

rammac

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It has to do with the bullet's velocity vectors and how they relate to the downward force of gravity. Shooting uphill will result in slightly less drop than when shooting downhill. Shooting uphill, less of the velocity vector adds to the downward pull of gravity.
 

speedengineer

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Do you know how Hornady is resolving their solution?
What MV and BC are you using?.
Mike,
Muzzle velocities I used in this comparison were 900 m/s (2953 fps) with a G1 0.625 bullet. 984mBar baro, 59F temp, 50% humidity. Check out the graphic I attached if you haven't seen it.

I recorded mRad and meters of drop from each of the calculator's output. Angular mRad or MOA correction values listed by all the different calculators should be comparable. Also, FYI, all the drop values in m/inches are corrected by each of the calculators to be drop as you'd measure it using your reticle. For a vertically oriented target located downwards from you at 30 degrees line of sight, bullet impacts viewed through the scope look closer together than they would measure using a ruler on the target. Corrected drop = ruler drop*cos(shooting angle). This shouldn't have anything to do with why Hornady's calculator gives different results, but I found it interesting to realize all of these calculators provide their results this way.
 

speedengineer

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Bumping this thread, looks like Hornady's ballistic calculators still disagree with other calculators when calculating solutions for uphill/downhill shots.

Ran some more detailed numbers today for a 7mmRM in both JBM and 4DOF. The difference between the solutions becomes VERY significant at larger angles and ranges. Not that a 40deg 1000yd shot is common....but hornady calculates 70 inches LESS than JBM does. A shot of 600yd at 30deg would still put you low by a foot!

1600475772004.png


1600475978974.png


200 yd zero
175 ELDX
0.705 BC G1
2900 fps
60F, 27.3 inHg
shooting uphill at the specified angle
no wind
 
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elkaholic

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Bumping this thread, looks like Hornady's ballistic calculators still disagree with other calculators when calculating solutions for uphill/downhill shots.

Ran some more detailed numbers today for a 7mmRM in both JBM and 4DOF. The difference between the solutions becomes VERY significant at larger angles and ranges. Not that a 40deg 1000yd shot is common....but hornady calculates 70 inches LESS than JBM does. A shot of 600yd at 30deg would still put you high by a foot!

View attachment 214805

View attachment 214806

200 yd zero
175 ELDX
0.705 BC G1
2900 fps
60F, 27.3 mBar
shooting uphill at the specified angle
no wind
That is VERY interesting and troubling!
Ive been shooting at 1200 yards at about 18 degrees uphill and have had some issues that weren't adding up. And yes, shooting too high by a considerable amount!!
 

speedengineer

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That is VERY interesting and troubling!
Ive been shooting at 1200 yards at about 18 degrees uphill and have had some issues that weren't adding up. And yes, shooting too high by a considerable amount!!
I take it you were using 4DOF? How high were you hitting, and with what cartridge? Extrapolating my chart via eyeball method to 1200 yards, 7mmRM would be about 35" high compared to the JBM calc.
 

Mikecr

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I believe Sierra has it right on slope shooting. They don't adjust range but apply the slope to shooting 'path'.
I use Pejsa ballistics myself, and have applied Sierra's method within this.
 

entoptics

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That is VERY interesting and troubling!
Ive been shooting at 1200 yards at about 18 degrees uphill and have had some issues that weren't adding up. And yes, shooting too high by a considerable amount!!
Are you using 4DOF?

I take it you were using 4DOF? How high were you hitting, and with what cartridge? Extrapolating my chart via eyeball method to 1200 yards, 7mmRM would be about 35" high compared to the JBM calc.
Unless I'm misreading the numbers, 4DOF would call for less correction, and therefore you'd be hitting low, not high.
 

elkaholic

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I have to make a correction. I guess its back to the drawing board as I was thinking backwards. I was using AB which is closer to JBM.
Im going back to where I was before I read this. I think I have a scope issue.
 

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