Calculators and reality aren't lining up

[SawyerH]

New to me rifle, new to me cartridge. Just need to enter everything into the app (4dof and AB) then go verify/ tweak the drag coefficients or velocity to match spot on.. right..

So reality doesn't agree with the calculators. Both 4DOF and AB seem to agree with each other however. So that's good.

6.5 147eldm 2660fps ( firing ese, 55degf, 40%, 30inHg, 7-10mph from nnw, 0-2° downhill)

Distance, Reality, 4dof , AB, (difference)
308yds 1.2, 1.29, 1.28, (+.09)
402yds 1.8, 2.1, 2.1, (+.3)
536yds 2.9, 3.3, 3.4, (+.4)
661yds 4.3, 4.6, 4.74 (+.4)
687yds 4.5, 4.9, 5.05, (+.5)
951yds 7.8, 8.4, 8.6, (+.7)


So the easiest way to line up the data is to tell the apps my scope tracking error is .905.. otherwise we're talking huge velocity and bc corrections. I was all excited to blame the scope until I ran a tall target test today and found it to be right on or maybe .1 mil shy of 10mil at 10 mil.

What gives? What have I missed? (other than the targets)
How am I off by roughly 10% at each distance?

 

[6.5SH]

I'd look at your zero, both distance and ATZ. Too often people assume their public/private range's stated "100 yards" is without verifying it.
If the center of your zero group is off and you can't dial to it use the offset function to correct for it.

 

[Matches Malone]

True ranges also, like mentioned above, but not just zero. At all distances. I have and many others have missed ranged things especially if there’s foliage and such around.

Was AJ turned off?

 

[SawyerH]

Good points. It takes about a 2" high zero at 100 to align the AB 687yd number. But that makes all the nearer values way off.

I use a vortex fury5000w/AB for all ranges. Open field, no obstructions

I had thought of the rangefinder being a source or error but it lines up with GPS pretty close. And it ranged the tall target which the scope measured quite accurately.

 

[SawyerH]

What is "AJ"?

 

[D̷e̷v̷i̷l̷D̷o̷c̷A̷Z̷]

What gives? What have I missed? (other than the targets)
How am I off by roughly 10% at each distance?

What BC are you using?

I plugged in all your data and my app is reporting pretty darn close to your reported numbers. I didn’t know your optic height. But I’m super close.

 

[SawyerH]

Both apps were using their own drag profile for the bullet.

If I toggle it to bc AB it says G7 .309, G1 .614

 

[6.5SH]

What is "AJ"?

Aerodynamic Jump

 

[SawyerH]

Turned the jump on and off not nearly enough change.

So far I can't duplicate those geo ballistics numbers with either one of my apps.

 

[ma smith]

I'd use a simple model like this...and double-check your inputs. its very common for people to lose track of what their calculator is doing.

https://bergerbullets.com/ballistics-calculator/

 

[SawyerH]

Ok, those geo ballistics numbers make sense. I didn't catch the 15° shooting angle in the screen shots.

I guess I should take a closer look at the depression angle of these targets it feels pretty flat. Maybe they are way down there.

 

[D̷e̷v̷i̷l̷D̷o̷c̷A̷Z̷]

Ok, those geo ballistics numbers make sense. I didn't catch the 15° shooting angle in the screen shots.

I guess I should take a closer look at the depression angle of these targets it feels pretty flat. Maybe they are way down there.

Happy accident. I must have tapped it after setting it at -2°

Let us know what you get for your angle at your next range day.

 

[JerkyFreak]

What altitude are you using?

Your pressure seems to be sea-level pressure, not station pressure.

 

[SawyerH]

1100' I was using pressure from a weather site. Actually showed 30.1 ish on the day of Shooting. I dont have a barometer on-site.

 

[JerkyFreak]

And you did measure the scope height from center of bore to center of tube?

 

[SawyerH]

2.03"