Garmin or ballistic app is wrong?

[Remington92]

I’m getting my rifle fine dialed for hunting season and left scratching my head comparing my Garmin xero to what ab mobile is giving me for dope. My rifle is a tikka ss 6.5prc chopped to 22” with a scythe on the end of it and I’m running factory 143eldx precision hunter. My Garmin gives me an average of about 2850 and the box says 2960 which jives with the shorter and slower tikka barrel. Out to 400yds my adjustments are dead on. Next target I reached out to is 800 yds and to get ab mobile to give me the correct elevation I had to slow down to 2780 or an extra 0.3 mil. I’m at 3200ft da for reference.

Is the garmin that far off or is there something goofy with what ab is feeding me? Also anyone ever have issues that you have to reload ab a couple times to get consistent values

 

[Wrench]

What your group size, wind, DA, DOF, BC....and have you tall targeted the rifle?

 

[Macintosh]

If your adjustment values are off a little that would do that—tall target should tell you.
Are all of your inputs correct? DA mainly, but also sight height, etc will affect it some.
BC is also going to be off—did you use a litz drag curve, or?

Fwiw Ive been starting with box velocity and using the ab truing function using all three distances, and it does work to get good dope from near to far…without a chrono I have nothing to compare it to though. Maybe thats a benefit?

 

[Remington92]

Group size today was just under 8” at 800yds. Not sure what tall targeting is but I did hang a piece of cardboard bout 3’ wide by 4’ tall with a target in the middle which is how I got my low impacts at 800. I checked DA populating on the app against my kestrel and that was good. Level open prairie without a stitch of wind today. I used the g7 bc that pre populated for the 143eldx in ab mobile. Double checked sight height as well. 1.5” with T084 rings is what I got.

 

[Macintosh]

How many rounds are you shooting at each distance to determine where group is centered?
How perfectly are you zeroed, and based off a 3,5, 10, etc round group?

 

[sveltri]

Is your scope height value correct?

 

[hereinaz]

Way more goes into truing ballistic solution than just velocity. Your Garmin’s velocity is not wrong. You’ve now seen it’s not as simple as putting in a couple values. Besides velocity, the BC of your bullet and rifle needs to be tweaked. BC is not a fixed number, it varies according to how the bullet may deform and by velocity.

Also check:

— your scope over bore height
— your turret to see if you dial one MOA or MIL and it actually moves it one full value. Scope turrets can be off by a few percentages, and more in worse situations.

And, many newish shooters find variation from day to day. The long range zero can easily vary because a shooter builds their position differently and control recoil differently from day to day.

 

[Remington92]

Way more goes into truing ballistic solution than just velocity. Your Garmin’s velocity is not wrong. You’ve now seen it’s not as simple as putting in a couple values. Besides velocity, the BC of your bullet and rifle needs to be tweaked. BC is not a fixed number, it varies according to how the bullet may deform and by velocity.

Also check:

— your scope over bore height
— your turret to see if you dial one MOA or MIL and it actually moves it one full value. Scope turrets can be off by a few percentages, and more in worse situations.

And, many newish shooters find variation from day to day. The long range zero can easily vary because a shooter builds their position differently and control recoil differently from day to day.

ok thanks I’ll tweak the bc and see if that’ll get me closer, I thought I’d read here before that it’s not best to tweak bc and rely on velocity which is why I started there.

 

[Remington92]

So I tweaked the bc and to get it to match my dope at 800 I had to drop the bc from .292 to .25 which seems waaaayyy off

 

[Wrench]

Step one is to tall taget test the tracking. You need to know you're running true to the click.....and is there any chance you have yds/meters mixed up?