Garmin xero or ab mobile 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?

 

[Emerson0311]

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?

The Garmin is almost certainly correct. AB is super solid if EVERY INPUT PIECE OF DATA is correct. I use both. That said, using a custom curve vs just a BC leaves room for error. Every time I have thought the solver is incorrect, I have found I used unsound data for one reason or another.

 

[Remington92]

For kicks and giggles I input the same info into hornadys app and it gave me the same dope at the lower velocity that i actually needed to make impacts.

I’m running
6.5 143 eldx in 1.8 twist barrel
1.5 scope height
2300’ da and 41 degree F
Tried both g7 and the cdm with similar results

 

[Emerson0311]

For kicks and giggles I input the same info into hornadys app and it gave me the same dope at the lower velocity that i actually needed to make impacts.

I’m running
6.5 143 eldx in 1.8 twist barrel
1.5 scope height
2300’ da and 41 degree F
Tried both g7 and the cdm with similar results

The AB solver will be correct if the inputs are correct. Hornady works until it doesn’t. Something is different about how the data is entered or used.

 

[Ledzep]

For kicks and giggles I input the same info into hornadys app and it gave me the same dope at the lower velocity that i actually needed to make impacts.

I’m running
6.5 143 eldx in 1.8 twist barrel
1.5 scope height
2300’ da and 41 degree F
Tried both g7 and the cdm with similar results

Sure that's correct? Most of my stuff ends up ~1.9-2.1" at the lowest.

 

[Remington92]

I’m running sportsmatch t084 medium rings directly to the receiver without bases. Double checked and I’m 1.7 actually. Entered that and didn’t seem to affect it.

 

[Remington92]

I also tried adjusting bc from .292 to .25 to get dope to match. That seems way off and unrealistic?

 

[Broncovan]

It isn't the Garmin.
I've shot the Garmin, magnetospeed and labradar at the same time. Average difference between the 3 was about 1 percent. None consistently high or low.

 

[Ledzep]

It isn't the Garmin.
I've shot the Garmin, magnetospeed and labradar at the same time. Average difference between the 3 was about 1 percent. None consistently high or low.

Aye, we've run 4-5 of them next to our Infinition doppler head and all were within 2-3fps on each individual shot and well within 1fps on the averages, SD's, etc.

 

[CK1.0]

If your chrono’d MV is correct and all your solver inputs are correct (twist, .264, height over bore, etc) then it’s your BC that’s off.

Remember, BCs change with different MVs, so don’t be worried about adjusting it.

FWIW, I see a lot of guys mess up their height over bore, mic from the middle of your rings to the gas bleed hole on your action and you should be good.

 

[HenryRed]

Try it without the scythe. See if that changes impact. I tried modifying a mdt comp brake to try and get more vertical reduction. Needed another .5 mil at 1000 yards. Did not notice at shorter ranges do to the size of plates or berm to see the splash.

 

[Mike Casselton]

If your chrono’d MV is correct and all your solver inputs are correct (twist, .264, height over bore, etc) then it’s your BC that’s off.

Remember, BCs change with different MVs, so don’t be worried about adjusting it.

FWIW, I see a lot of guys mess up their height over bore, mic from the middle of your rings to the gas bleed hole on your action and you should be good.

Agree. The OP needs to adjust BC at 800. The change is small and honestly should be the number on the right. Going from .292 to .25 is way too much.
Try going to .285 and see if that matches up to your actual impact.

 

[Ledzep]

If your chrono’d MV is correct and all your solver inputs are correct (twist, .264, height over bore, etc) then it’s your BC that’s off.

Remember, BCs change with different MVs, so don’t be worried about adjusting it.

FWIW, I see a lot of guys mess up their height over bore, mic from the middle of your rings to the gas bleed hole on your action and you should be good.

Especially with people using 20, 30, 40 moa bases and/or mounts, the most accurate method is actually to measure at the objective bell. The image that the reticle is imposed onto, and that the erector tube "looks around at" is generated from the objective bell. Outside-to-outside widest measurement between the barrel and objective, then subtract half the barrel diameter and half the objective lens.

Also, bear in mind there are many factors that play into discrepancies at range. MV is pretty easy to nail down with modern chronographs, Height over bore is pretty easy to nail down. Twist rate is easy enough to measure and fairly trustworthy from the barrel mfgs. A 100yd zero is +/- <1/2 the value of a click (or some scopes even less)....

However, to correct for drag at distance you are also making the assumption that;
- Your optic tracks true
- Your zero is where you think it is
- The atmosphere isn't obscuring LoS (mirage, lighting, color abberations, etc.)
- Your aim point is perfect
- You dialed what you think you dialed
- The wind has no vertical component
- Horizontal wind is being accounted for correctly (aerodynamic Jump)
etc.

And that drag alone is the reason for the discrepancy in your vertical POI. It's entirely possible you're on top of all of those things, and it's also entirely possible for all of those minor things to add together in the same direction. Just something to keep in mind. Recording as much data at the range is paramount to sorting these issues out.

 

[Buford Boone]

I've never found a radar measured drag function done by a competent source to be "Goofy". They offer the most accurate description of drag available - but for the "system" (rifle and bullets) that was actually shot over the radar.

Shoot the same bullets in a different barrel and your results may be a little bit different. Same goes for different lot of the same type of bullets, etc.

Radar testing is easy mainly because someone else is doing the hard part of paying for it and running it and None of the stuff Ledzep mentions about assuming:

- Your optic tracks true
- Your zero is where you think it is
- The atmosphere isn't obscuring LoS (mirage, lighting, color abberations, etc.)
- Your aim point is perfect
- You dialed what you think you dialed
- The wind has no vertical component
- Horizontal wind is being accounted for correctly (aerodynamic Jump)
etc.

Can change the radar data.

Radar that tracks a bullet a reasonable distance is expensive. There are systems that claim to track to about 100 yards.

Anyone that uses 100 yard drag data to make long range predictions deserves what they get.

Want to predict long range performance? Measure at the distance you plan to shoot.

Even if you were rich and bought one of those medium range radar systems, learning to use it may prove problematic.

How can the average shooter measure drag discrepancies?

Measure muzzle and down range velocity or MV and Time of flight. Like radar, neither of those methods care about any of the stuff Ledzep pointed out.

 

[Clearlight]

AB and CDC’s are the jam. All radar chronos estimate muzzle velocity based on multiple data points. Even with CDC’s I have had to tweak a few fps vs chrono to true for my barrels. Beats the crap outa running BC’s and running different tracks depending on target range bracket… Anyone going to or beyond SS with a decent size calibre will know. Short range and a zippy 6 mm less so…