Using DA instead of BP/Alt/Temp throws off Ballistic calc

3of30

3of30

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Good evening,

I am currently using AB for my clac. I have never been able to get my actual shooting results to match up with my ballistic calc charts. I have been shooting and competing for a couple of years now, and whenever I stray from my home range and rely on my calc for data it is way off. It usually takes me two stages to get my Dope right then all is good. Which is annoying at best..

So today I loaded up some rounds and hit the range. I verified my zero, and drops for 100m, 200m, 300m, 500m and 800m (all the range had for distances).

When I plugged the current weather condition into the calc from my kestrel the drops were close (within .3m for most, not as close as id like). Also I was chronoing all my rounds and using the average for the calc (SD around 9.0).

Then when I change my AB app settings to use DA instead of BP, Alt and temp, the numbers are way off.

Example: DA taken from my kestrel was 660M. Plugged it into AB and my trajectory chart was way off. If I ramp my DA to 2000M in the AB app my trajectory chart lines up with my actual drops.

How can this be when 660M is the reading taken from my kestrel?

Any help would be much appreciated.

Shooting AIAT 6.5CR
140 ELD-M 41.5gr H4350
 
So if I'm understanding you correctly, your ballistic app never gives you the correct dope (ie your only correct dope is what you've actually recorded at your home range)? If you enter all the atmospherics correctly and your dope doesn't line up, you need to true the BC of the bullet that you're using so that it does. A bullet's BC isn't necessarily going to be the same in every different barrel and load combo.

If switching from using barometric pressure, altitude and temp to DA changes your dope, you're inputting something incorrectly somewhere. DA is basically an aggregate of pressure, temp and humidity.
 
rugbydave said:
So if I'm understanding you correctly, your ballistic app never gives you the correct dope (ie your only correct dope is what you've actually recorded at your home range)? If you enter all the atmospherics correctly and your dope doesn't line up, you need to true the BC of the bullet that you're using so that it does. A bullet's BC isn't necessarily going to be the same in every different barrel and load combo.

If switching from using barometric pressure, altitude and temp to DA changes your dope, you're inputting something incorrectly somewhere. DA is basically an aggregate of pressure, temp and humidity.
Click to expand...

I have messed with the BC before, but have not had great results. I will try again.

As far as DA what you are saying is exactly what I thought and why I do not understand the trajectory change. All the values I am entering are directly from my kestrel.
 
I do not know if this is revelant or will help you...
I have a different app and different caliber, my kestrel is a 5000 series with DA and blutooth link,

When I first started shooting beyond 500M, my ballistic app (strelok pro), was way off, something like 0.3mil off at 600 and having me miss a figure 11 at 700M.
Since I have played with the BC of my bullet in settings, and set it to multiple BCs, my app is now bang on at 200-800M, absolutely bang on.
Was 0.1mil off at 900M last outing.

This is how I set up my multiple BC to give you an idea.

tTyAmcLh.png


The app by default it was .505 for 175 SMK, so when it was using that BC I was off.
Sierras site says .505 @ 2800 fps and above
 
EC said:
Is your Barometric Pressure set for station pressure or is it corrected?
Click to expand...

it is corrected for my current altitude. But I was just reading up on the kestrel site and they recommend always changing your reference alt wherever you go (rookie mistake by me). So that may help with the Dope being off. Also I will play with my BC as seen above.
 
There is a race track close to where I live that has all the atmospheric conditions listed on its website. My Kestrel matches the Alt, BP and Temp. But the DA is way off on my kestrel. (Kestrel DA 798m, Racetrack DA 457m). When I input all my kestrel conditions into a DA calc online it comes up with the same DA as the racetrack. So it would seem my internal DA calc in my kestrel is off? I will contact kestrel and see what they say. But in the mean time I will just input all three conditions instead of DA.
 
I'm wondering about a couple things here...

1) Isn't AB supposed to pull the BC from Litz tested values over a doplar radar? The library BCs are supposed to be accurate.... So I'd be inclined not to tweak this.
2) Some scopes do not track as accurately as you might think. Have you calibrated the scope tracking to be sure that isn't the problem.

So if the scope tracks and the BC is actually correct and pulled from the AB library, that leaves atmospherics.

Are you sure you haven't gotten too creative while adjusting things to replicate your home range ballistics?

Maybe just go back to the basics, and set up another profile from scratch using AB library for bullet, actual chronograph values and then just fiddle with atmospherics only.

BTW, the Kestrel is what it is, but it is not your only option for atmospherics... There are all sorts of plain old weather stations you can find at places like Canadian Tire, and Home Depot, not to mention just about anything from Amazon.

I use a Garmin 701 in the field and it does not have humidity... So I have a few portable weather devices that I bring along for that. Humidity for example is not a huge influence, but at least I have it if I want it.

Other devices will confirm barometric pressure as well. Sometimes devices do not all agree so for not much money you can buy a few to find what seems to work best.

https://www.amazon.ca/Altimeter-Hand-held-Multifunction-Electronic-Altiemeter/dp/B0786XTGM2/ref=sr_1_15?keywords=barometer&qid=1557247050&s=gateway&sr=8-15

https://www.amazon.ca/ThermoPro-Thermometer-Hygrometer-Cold-Resistant-Temperature/dp/B07GW9MGFH/ref=pd_sbs_86_5/136-2129616-3253419?_encoding=UTF8&pd_rd_i=B07GW9MGFH&pd_rd_r=d6fd593a-70e5-11e9-ad11-c3d8451968d7&pd_rd_w=PcqNQ&pd_rd_wg=BSetV&pf_rd_p=5dcda75b-8643-4da3-9bb1-5c0233790500&pf_rd_r=4XEYYA310SH9EK1SBDBD&psc=1&refRID=4XEYYA310SH9EK1SBDBD
 
Last edited:
Maple57 said:
I'm wondering about a couple things here...

1) Isn't AB supposed to pull the BC from Litz tested values over a doplar radar? The library BCs are supposed to be accurate.... So I'd be inclined not to tweak this.
2) Some scopes do not track as accurately as you might think. Have you calibrated the scope tracking to be sure that isn't the problem.

So if the scope tracks and the BC is actually correct and pulled from the AB library, that leaves atmospherics.

Are you sure you haven't gotten too creative while adjusting things to replicate your home range ballistics?

Maybe just go back to the basics, and set up another profile from scratch using AB library for bullet, actual chronograph values and then just fiddle with atmospherics only.

BTW, the Kestrel is what it is, but it is not your only option for atmospherics... There are all sorts of plain old weather stations you can find at places like Canadian Tire, and Home Depot, not to mention just about anything from Amazon.

I use a Garmin 701 in the field and it does not have humidity... So I have a few portable weather devices that I bring along for that. Humidity for example is not a huge influence, but at least I have it if I want it.

Other devices will confirm barometric pressure as well. Sometimes devices do not all agree so for not much money you can buy a few to find what seems to work best.

https://www.amazon.ca/ThermoPro-Thermometer-Hygrometer-Cold-Resistant-Temperature/dp/B07GW9MGFH/ref=pd_sbs_86_5/136-2129616-3253419?_encoding=UTF8&pd_rd_i=B07GW9MGFH&pd_rd_r=d6fd593a-70e5-11e9-ad11-c3d8451968d7&pd_rd_w=PcqNQ&pd_rd_wg=BSetV&pf_rd_p=5dcda75b-8643-4da3-9bb1-5c0233790500&pf_rd_r=4XEYYA310SH9EK1SBDBD&psc=1&refRID=4XEYYA310SH9EK1SBDBD
Click to expand...

They only pull the BC if you buy the custom drag, which I just did to try it. Dope did not change...

Scope is a vortex razor, from all the reviews and tests ive read they seem to track well. Although I have not tested mine. But when shooting all day the drops are repeatable every time so I believe it tracks well and does not have the infamous "ghost click".

My Kestrel readings are dead on to the local weather stations (minus DA as explained above)
 
3of30 said:
They only pull the BC if you buy the custom drag, which I just did to try it. Dope did not change...

Scope is a vortex razor, from all the reviews and tests ive read they seem to track well. Although I have not tested mine. But when shooting all day the drops are repeatable every time so I believe it tracks well and does not have the infamous "ghost click".

My Kestrel readings are dead on to the local weather stations (minus DA as explained above)
Click to expand...

You need to do a tall target test to figure out the actual adjustment increments of your elevation turret. The best scopes in the world will have some variability in this regard from sample to sample.

You would also be better off to use station (absolute) pressure at your location, rather than baro pressure which introduces a relative measurement and correction into the equation. Forget the local weather stations. If your Kestrel reads 26.3 InHg, input exactly that into your app, and make sure you set it to absolute pressure.
 
Are you using AB on an iPhone?

It can be buggy as heck and before I switched to a Kestrel Elite AB I had to remove and reinstall AB regularly to get reliable data
 
Great advice here.

I would also do the following.
Record your dope via actual drops.
Play with atmospheric using known V.
Once AB aligns with actual drop values, play with atmospherics in AB (temp first) then see what the temp value is that causes an incremental change in dope as outlined in AB.

Do the same with pressure.

Record these values.

Shoot again on a different day using only temp values and pressures as outlined on a calibrated kestrel.
Adjust your come up's using the values you recorded with earlier experimentation of temp and pressure.

Doing this you should now have accurate data as to what temp and pressure values actually do to your rifle rounds.


Do a tall target tracking test also to confirm the optic.
Good luck.
 
Did you record actual click values at actual distance and weather conditions?
If so open up JBM ballistic on the computer and see if real world values are in line with JBM, big chances are yes and your phone ballistic app needs some BC truing.
 
Applied ballistics has always ran like sh*t on both my phones, more often then not it would give me different dope for a given range each time I pulled a chart without me changing any variables. I went back to using ballistic AE and use weather conditions as absolute then use kestrel reading for BP/temp/humidity.
 
I have also had bug issues with AB, I also have found that the G7 Bc of the 140ELD-M on AB is listed as .291, when I used this BC it did not match my results, I use .311 have found that to work well, I have tested that BC out to 1000M.
I use StrelokPro for my ballistics, works great. Hope that helps.
 
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