How can 2 Ballistic Calculators be so different?

[skibumdc]

Is the Shooter App that bad?

I will preface that I'm comparing the Shooter App vs AB Quantum Free...for now

600 yards 6.5CM
Shooter app said 5.3MIL up, which is what I used.
It started pouring rain, we were prone out in the elements, and range closed due to Tornado warning, so couldn't experiment/troubleshoot
I came home confused and downloaded AB Quantum.
AB said 3.8MIL
That's a HUGE difference.
Same rifle and bullet data input

Shooter app I had plugged in G7 from factory box @ .311 BC
AB is saying 3.06 BC, so I Used that for AB app

I'm obviously inclined to believe AB since Shooter led me WAY too high for MIL adjustment, but AB seemed just a tad low in my head.
1.5MIL @ 600 yards would be below +/-32" and therefore possibly off the 36" target paper?

Backstory,
Zero'd rifle after scope & chassis install, and chrono'd ammo @ 100 yards, w/ Garmin.
Attempted 1000 yard and was WAY high, not even on paper.
Went back to 100 yard range and reworked zero, minimal change. It was windier that day but shouldn't affect vertical.
2 weeks later shot @ 600-yards, and again, shot very high, but at least on MR1-C paper, about 15-18" high, didn't get a true measurement. Can post a pic later Tight enough group that I don't doubt torque values, but will re-verify.
We were at 40 feet elevation @ Marine Corp Base Quantico.
74*F/70%RH by Accuweather app. Winds negligible. Yes...I'd like a Kestrel for true readings. lol.

Ammo:
Federal Gold Medal Match Berger Hybrid Target 140gr
Chrono'd Velocity 1760fps
SD by Garmin as 7, not too shabby for Factory ammo

Rifle Data:
New build Impact 737R, Stuteville 26" CRB 6.5CM 7.7-twist Comp profile. About 140 rounds total through the barrel so far.
MDT ACC Premier Chassis
Arken 7-35x scope
Sight leveled in MDT rings w/ Arrow products scope leveling tool, and verified w/ SG Pulse electronic level.
Height of scope over bore inputted as 1.5" but definitely need to go re-verify as I know this can cause a multitude of issues

 

[Lowlight]

The short answer is, the author adds in what i call flourishes or what can be described as biases to each program. While many programs will use the same Engine, the writer can augment them.

All software must be trued, they are almost never correct out of the gate, my recommendation is to use Gravity Ballistics to feed your solver after it has been doped.

A 6.5 at 600 yards is about 3.4 to 3.6 mils

But use Gravity Ballistics first, then add in the data to your solver it will work right

 

[DocUSMCRetired]

Is the Shooter App that bad?

I will preface that I'm comparing the Shooter App vs AB Quantum Free...for now

600 yards 6.5CM
Shooter app said 5.3MIL up, which is what I used.
It started pouring rain, we were prone out in the elements, and range closed due to Tornado warning, so couldn't experiment/troubleshoot
I came home confused and downloaded AB Quantum.
AB said 3.8MIL
That's a HUGE difference.
Same rifle and bullet data input

Shooter app I had plugged in G7 from factory box @ .311 BC
AB is saying 3.06 BC, so I Used that for AB app

I'm obviously inclined to believe AB since Shooter led me WAY too high for MIL adjustment, but AB seemed just a tad low in my head.
1.5MIL @ 600 yards would be below +/-32" and therefore possibly off the 36" target paper?

Backstory,
Zero'd rifle after scope & chassis install, and chrono'd ammo @ 100 yards, w/ Garmin.
Attempted 1000 yard and was WAY high, not even on paper.
Went back to 100 yard range and reworked zero, minimal change. It was windier that day but shouldn't affect vertical.
2 weeks later shot @ 600-yards, and again, shot very high, but at least on MR1-C paper, about 15-18" high, didn't get a true measurement. Can post a pic later Tight enough group that I don't doubt torque values, but will re-verify.
We were at 40 feet elevation @ Marine Corp Base Quantico.
74*F/70%RH by Accuweather app. Winds negligible. Yes...I'd like a Kestrel for true readings. lol.

Ammo:
Federal Gold Medal Match Berger Hybrid Target 140gr
Chrono'd Velocity 1760fps
SD by Garmin as 7, not too shabby for Factory ammo

Rifle Data:
New build Impact 737R, Stuteville 26" CRB 6.5CM 7.7-twist Comp profile. About 140 rounds total through the barrel so far.
MDT ACC Premier Chassis
Arken 7-35x scope
Sight leveled in MDT rings w/ Arrow products scope leveling tool, and verified w/ SG Pulse electronic level.
Height of scope over bore inputted as 1.5" but definitely need to go re-verify as I know this can cause a multitude of issues

This is pretty far off. I would double check the data in Shooter. It shouldn't be 3 mils off. Possibly inclination? Maybe something else, but that is pretty far off. I would scrub the profile and inputs.

 

[Baron23]

Yeah, first the OP must have meant 2760 and not 1760

And I have trued Prime ammo w 142 SMK (.301 G7) at 500 meters (500 meters and longest I have regular access to) and I get 3.62 mil at 600…but I use Hornady 4DOF w drag curves rather than G7.

So, your Shooter App is way off, IMO. I’m not familiar w that app so have no suggestions on source of error.

Also, you have a heavy barrel in a top shelf chassis and a scope w 34mm tube. I’d def check that 1.5” height above bore figure.

But of course, even if in error, both apps used the same height so this doesn’t explain where Shooter App came up with this crazy number.

Cheers.

 

[Long Range 338]

Your post shows 1760 for velocity. Certainly this is supposed to be 2760 fps. Maybe one of the profiles is off by 1k?

 

[skibumdc]

Your post shows 1760 for velocity. Certainly this is supposed to be 2760 fps. Maybe one of the profiles is off by 1k?

Yes, apologies, fps were fat-fingered in main post. Velocities should be 2760, and verified in both Shooter and AB.
BTW, I DID figure out in Shooter where the issue occurs, but it doesn't make sense.

If you use the built-in Berger 140 Hybrid match bullet, it gives the correct MIL for 600 yards.
If you manually entered the SAME info, it gives a way higher MIL calculation for 600 yard. I had initially looked under Federal and didn't see the ammo so I manually entered the data, identical to the website info. When I looked under just the projectile manufacturer, Berger, the 140 match hybrid target was listed....so I chose that and it gave me the correct MIL data.

Appreciate the help guys. Truly.
Back to the range to try and hit some better groups and X's @ 600 yards