Using DA instead of BP, Alt and temp, throws off AB trajectory chart

[3of30]

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

 

[VegasHKShooter]

Rule number 1, pay the $1.99 for the CDM. It is based on Litz and his team shooting the heck out of the specific rounds, NOT using a standard, non changing B.C. Using a standard B.C. doesn’t take into account the different things bullets do as they slow down.
A 140 ELD-M might be a .250 G7 at 2700 (pulling numbers out my ass, just follow along), but that B.C. changes as the bullet slows down. The CDM account for this.
I always plug in the Humidity, the Barometric Pressure, and the Temp. Then I hit the “pressure is absolute” button. When using the CDM’s, and giving the parameters I give, I’m extremely consistent out to past 1000yds. I shot the Arizona Axis Works Long Range Challenge using this, and had hits out to 1100 with my GAP-10 6.5CM. Also shot Jack Leuba and Ash Hess's Gas Gun shoot at The Arena in Georgia with my 5.56 LPR. Had hits there out to 1160 with a 5.56. ?

As long as your settings are correct, and your velocities are correct, you will be very accurate.

There is a good explanation on the KAC forum over on ARF.com. Look at the top of the page. Dude goes step by step on how to set it up. He is my shooting partner, and he taught me.

 

[ShtrRdy]

I wonder if you would use absolute pressure and not have to enter altitude if that would help?

 

[VegasHKShooter]

Yes....I should have said: when I entered altitude AND “pressure is absolute” it threw me off. I leave altitude alone.