Is AB Quantum calculating wrong? New to calibration....

[Chukwithak]

So I've been trying to watch Docs videos. I have a Garmin we use to Chrono a Kestrel that I record atmospherics when zeroing. (I know it's overkill)

I'm using AB bullet library G7 for a 7RM 24" barrel, Hornady ELDX 162 grain.
His velocities at barrel are 2878, 99y range, sight height 1.81, 9.50 twist. (SG 1.44)

1. Zero - (w/ Kestrel 5700X recording during zero and taking the average)
   • Temp 71F
   • Pressure 25.11
   • 38% humidity
2. Zero Height/Offset - Hornady Group Analysis app
   • 0.17 Elevation
   • 0.76 Eindage
   • He was high and right.
3. Then a tall target test. Again used the Hornady Group Analysis app
   • SSF Windage - 0.92
   • SSF Elevation - 1.16

Then we shot to 1185 yards and the ABQ app was calling for 10.35E and he missed high. We dialed him down to 8.9E. When I put this in the CDF, it won't apply. It reverts to an elevation of 10.35. The weird thing is that if I remove the Zero height/offest and SSF E/W, ABQ gives the correct dope of 8.9E. Again, this is my first time digging into these details. We have never shot far enough to feel that we need this data, but now we are starting to push beyond 1k.

Does anyone have any thoughts?

 

[Chukwithak]

@DocUSMCRetired Any thoughts?

 

[DocUSMCRetired]

Their would be a lot to break down to figure this out.

Is the zero range correct? A Rangefinder has a margin of error.

Is the zero offset caused by the shooters positional shooting? Is it repeatable?

For the SSF adjustment, was the distance measured with a tape measure from the windage turret to the target? Using a range finder for this is not advised.

Kestrel doesn't have the CDF function at this time.

Was the SSF calculated based on the formula provided in the user manual?

 

[Chukwithak]

Bought a 100yd measuring tape to take with us for confirmation. Haven't been back out yet.

We did not calculate SSF; we used the Hornady app shot analysis data.

Just a thought, and maybe something to be built into AB quantum? Since LRFs can have errors just like our rifles, can we add an LRF correction to our profile? I'm probably overthinking it. I tend to do that kind of stuff.

I'll retest my buddy's stuff with the 100-yard tape and return with the outcome.

 

[Evintos]

Why use G7 instead of the CDM? CDM calls for a 9.1E hold.

 

[Chukwithak]

Why use G7 instead of the CDM? CDM calls for a 9.1E hold.

View attachment 8750847

I wanted to create a CDM for his setup. Assuming I was doing everything correct. 9.1 would’ve still too high as 8.9 was the correct hold.

 

[Evintos]

I wanted to create a CDM for his setup. Assuming I was doing everything correct. 9.1 would’ve still too high as 8.9 was the correct hold.

9.1E is much closer than the 10.35E and that was just using the basic info and the CDM (Temp 71F, Pressure 25.11, 38% humidity, 2878fps, 99y range, sight height 1.81, 9.50 twist)

I just tried adding the SSF and sight offset and it was giving me values in the 10.5 range for elevation.

If I had to guess, the Hornady Group Analysis app is giving you erroneous values for the SSF and offset. SSF is the one that is causing the biggest error.

Never used the app but I'm assuming it requires you taking a picture of your target and if so that's probably where some of the error is coming from. Off angle camera that the app can't compensate for when taking a picture for the analysis app.

 

[Chukwithak]

9.1E is much closer than the 10.35E and that was just using the basic info and the CDM (Temp 71F, Pressure 25.11, 38% humidity, 2878fps, 99y range, sight height 1.81, 9.50 twist)

I just tried adding the SSF and sight offset and it was giving me values in the 10.5 range for elevation.

If I had to guess, the Hornady Group Analysis app is giving you erroneous values for the SSF and offset. SSF is the one that is causing the biggest error.

Never used the app but I'm assuming it requires you taking a picture of your target and if so that's probably where some of the error is coming from. Off angle camera that the app can't compensate for when taking a picture for the analysis app.

I’ll try it with the CDM and report back. Not sure why the CDM vs G7 would be so erroneous.

 

[Chukwithak]

9.1E is much closer than the 10.35E and that was just using the basic info and the CDM (Temp 71F, Pressure 25.11, 38% humidity, 2878fps, 99y range, sight height 1.81, 9.50 twist)

I just tried adding the SSF and sight offset and it was giving me values in the 10.5 range for elevation.

If I had to guess, the Hornady Group Analysis app is giving you erroneous values for the SSF and offset. SSF is the one that is causing the biggest error.

Never used the app but I'm assuming it requires you taking a picture of your target and if so that's probably where some of the error is coming from. Off angle camera that the app can't compensate for when taking a picture for the analysis app.

I dont know why, but now all of the sudden CDF if working. I'll be in the field to go through all of this again on Friday. Thanks for your time on this. I'll follow up wether it's working or not.

 

[Evintos]

I dont know why, but now all of the sudden CDF if working. I'll be in the field to go through all of this again on Friday. Thanks for your time on this. I'll follow up wether it's working or not.

It's definitely the SSF value being the culprit. G7 outputs 9.12E so only +0.02 difference from the CDM. Adding the offsets changes the solution by +0.01 (9.13E output). Pic below with G7, offset and the SSF value. With the SSF the output goes to 10.59E. Definitely double check the SSF.

 

[Emerson0311]

Using a Hornady app to check or produce data for the AB app is not sound. Kind of like using rules of thumb instead of math. Perhaps each have their place, but not together.

 

[Ronws]

I don't know if we can go by recommendations of others but sometimes a practical application is best.

At Northeast Texas Tactical in Terrell, Texas, they offer training and a range that goes to a mile. They require you have some kind of ballistic solver and recommend AB (now AB Quantum.)

While AB was not as easy to use as Strelok Pro or 4DOF, the ability to build your own CDM is key, I think, to consistency.