Truing Ballistic Software: 4DOF or AB - amount of required correction

[MaraviaDave]

This is a question for users of Hornady 4DOF or Applied Ballistics solvers, who are using bullets with Custom Drag Models (CDM) found in the solver's database. (As opposed to using G1 or G7 BC's)

Hornady 4DOF: What was the Axial Form Factor number required to true your software?

Applied Ballistics: What percent (%) adjustment to your muzzle velocity was required to true your software?

I use both software types, each loaded on Kestrel 5700 weather meters. I'm curious if other's experiences are similar to mine, in regards to the amount of required correction, while truing software.

 

[MaraviaDave]

Okay, let’s broaden this question a little.

Are you truing your ballistic software? If so, at what distance? What method are you using? How much correction is required.

 

[Lawnboi]

I’ll start by saying I rarely shoot into transonic range. Very rarely, just don’t have the opportunity around home. I also don’t shoot goofy bullets, I shoot bullets that are pretty well known where cdm’s can easily be found for them.

With that said, Iv used both calculators above, and to be honest, with well known bullets, truing has done me more harm than good. Usually I ended up truing to my position, my daily shooting habit or the environment.

Back when I started shooting longer range I had the opportunity before a match to shoot my ammo at 1k to true. Big plate out there, got it centered up, and changed my axial form factor. Heavy mirage, not all uncommon for summer here. Had read everywhere about truing so I did.

Next weekend was the match, dope was off until I changed back. The match did not go well.

Equipment limitation also can cause you to have to true. Think 10 mils is actually 10.2 ect.

If your off more than a click or 2, with a well known bullet, you better start evaluating your surroundings and equipment before messing with computer inputs.

That’s not to say I’d never true. But you can get a long way on a good velocity, a perfect zero, good equipment and good mechanics.

Last match I hadn’t been able to shoot that specific bullet very long, only 400 yards. Showed up with the above. My dope was fine both days to a thousand.

That’s just my 2 cents on truing. Good tool to have but you have to know when not to use it.

 

[MaraviaDave]

Taking another stab at this…….looking for feedback on the question raised in post #1 or post #2, from anyone who understands and has actually followed the correct process for truing ballistic software (AB, 4DOF) using CDM’s (preferably) or G1/G7 drag models.

 

[pyrotechnic]

If I do any tweaking to mv or BC, I generally use MV to make corrections to dope around 600yds I will then make a small correction in BC at distances past that.

As the above poster mentioned, I have definitely encountered making a tweak, especially to bc, and then changing it back the next range session as whatever was occurring make the correction seem necessary was not present at the other location/time.

If you're finding that you're having to make large connections to a known MV and BC there's a good chance that you have something else going on.

 

[LaHunter]

Taking another stab at this…….looking for feedback on the question raised in post #1 or post #2, from anyone who understands and has actually followed the correct process for truing ballistic software (AB, 4DOF) using CDM’s (preferably) or G1/G7 drag models.

I use the G7 drag model with my Kestrel 5700 Ballistic. My MV truing was less than 1% adjustment from my labradar mv average. I trued at 775 yards. My dope before truing vs after truing at 775 yards was only .5 moa.
Hope this is helps

 

[MaraviaDave]

I use the G7 drag model with my Kestrel 5700 Ballistic. My MV truing was less than 1% adjustment from my labradar mv average. I trued at 775 yards. My dope before truing vs after truing at 775 yards was only .5 moa.
Hope this is helps

Thanks for sharing your experience. This is the type of data I'm hoping to gather from this thread. My truing experience, using G7 drag models using AB in a Kestrel 5700, has been similar (%) to yours.

What cartridge, G7 BC value and starting MV was used for the example above?

(I'm thinking in terms of BC velocity dependence)

 

[MaraviaDave]

As the above poster mentioned, I have definitely encountered making a tweak, especially to bc, and then changing it back the next range session as whatever was occurring make the correction seem necessary was not present at the other location/time.

In general, my speculation is that if this is occurring the errors are most likely one of two things. 1) Lack of consistency of the shooter behind the rifle (e.g. wandering zero). 2) Improper inputs into the ballistic solver (e.g. environmentals).

 

[BjornF16]

How accurate is your chronograph? Is it calibrated? What was your ammo temp when you chronographed it? Have you measured the MV at varying temps? Are you using same lot of ammo, powder, bullet?

All that said, the bullet doesn’t lie.

I’m running Kestrel 5700 Elite with AB. I’ve watched a bunch of the Kestrel videos and have sat in on their classes. They are convinced CDM are the way to go if using AB.

I played around with different G7 BCs trying to find a better fit for supersonic ranges only (for hunting I’m not shooting into transonic). The CDM with trued velocity at 750 yards was best fit (less than 1% change in velocity for truing).

If you true velocity closer than 85% to transonic, then Kestrel says not to trust anything beyond the transonic threshold with that value. Works fine for anything inside that range.

 

[MaraviaDave]

How accurate is your chronograph? Is it calibrated? What was your ammo temp when you chronographed it? Have you measured the MV at varying temps? Are you using same lot of ammo, powder, bullet?

Great point! From my perspective, having the option to have Temperature vs. Muzzle Velocity sensitivity data inputted into a Kestrel 5700 (AB or 4DOF) is a very valuable feature.

For those not aware…once your Kestrel pulls a temperature reading…the software will look up the Temp/Velocity table and then assign the corresponding MV as one of the inputs while deriving a ballistic solution.

I feel like this feature, along with accurately updating current environmental conditions, is key to successfully truing ballistic software.

 

[LaHunter]

Thanks for sharing your experience. This is the type of data I'm hoping to gather from this thread. My truing experience, using G7 drag models using AB in a Kestrel 5700, has been similar (%) to yours.

What cartridge, G7 BC value and starting MV was used for the example above?

(I'm thinking in terms of BC velocity dependence)

7 mm rem mag. 160 gr Accubond bullets. G7 is .236. MV from labradar, before truing, was 3085 fps.

 

[MTNHUNTER76]

Okay, let’s broaden this question a little.

Are you truing your ballistic software? If so, at what distance? What method are you using? How much correction is required.

All ballistic calculators need to be trued. Get on YouTube and search videos from Bryan litz or Todd hodnett. This will explain truing and how to properly accomplish it.

 

[MaraviaDave]

All ballistic calculators need to be trued. Get on YouTube and search videos from Bryan litz or Todd hodnett. This will explain truing and how to properly accomplish it.

You’re missing the actual question and purpose of the post.

It’s not a question of whether or not ballistic solvers need to be trued, or how to do it.

But rather, a question for people that are using AB or 4DOF software, ideally loaded onto Kestrel 5700’s, shooting bullets found in the CDM library.

Specifically, what percentage of Muzzle Velocity correction is required to true AB. Or, amount of Axial Form Factor correction is required to true 4DOF.