Disparity between kestrel AB and Hornady 4Dof

[Raufoss]

Hey guys I need to be enlighten...

So I am comparing my kestrel elite AB with the 4 Dof app.

Data is the same in both :
0.224 75gr eld-m (custom curve in AB vs 4 Dof hornady)
2938 fps
100 yards zero
1-7 twist
Environmental are identical with a 10 mph wind at 270°

When I compare data everything line up spot on until 900 yards. Past that there is 0.1 to 0.3 mils difference up to 1200 yards( Hornady is giving higher number). If I turn on a tail wind on the Hornady 4 Dof the data line up with AB.

Is Hornady is applying more AJ than AB? Or it's simply that the custom curve is alot different than the doppler data that hornady as in the 4 Dof?

 

[Dthomas3523]

Answer could be a multitude of things.

Most important thing is if you can get them both to true up properly with your real world data.

Looking for answers to these types of questions will drive you nuts.

 

[Raufoss]

Lol I'm already nut..

I've just never push my load past 100p yard and have target at 1200 this weekend at a match.. I'd like to know why and which to trust.

 

[Dthomas3523]

Lol I'm already nut..

I've just never push my load past 100p yard and have target at 1200 this weekend at a match.. I'd like to know why and which to trust.

If it were me, I’d use the kestrel custom curve for your round with your chrono’d velocity.

Really need to true your date before. But if you don’t have time for that, that’s what I’d do.

 

[Dthomas3523]

Not truing before taking a 75gr to 1200 is gonna make it tough. Regardless of software.

Hell, even trued ain’t gonna be easy.

 

[lumberjack78]

If it were me, I’d use the kestrel custom curve for your round with your chrono’d velocity.

Really need to true your date before. But if you don’t have time for that, that’s what I’d do.

Agreed with truing if you have a chance. Does the AB account for aerodynamic jump like the 4DOF program? That could be the difference.

 

[Dthomas3523]

Agreed with truing if you have a chance. Does the AB account for aerodynamic jump like the 4DOF program? That could be the difference.

I need to familiarize myself with 4dof more.

But kestrel will figure aerodynamic jump if wind1 is active. If wind1 is set to zero, it will not figure in aerodynamic jump.

So, checking the difference with and without wind1 will show if that’s the difference.

Also, if .3 is the biggest difference between 900 and 1200, and truing is not a possibility, just go halfway in between what 4dof and kestrel is calling.

 

[Steel head]

I’ve found the 4dof to work really well especially with Hornandy bullets.

I also prefer changing the AFF on 4dof than fiddling with FPS and/or BC on AF.

No matter what it’s hard to get one absolutely perfect curve from 100 to 1800 with AB.
I usually make two curves on AB.
One for 0-1200 and one for 1000-1800 or so.

With the Axial Form Factor I can do it with one but I prefer the functionality of the Other app.

 

[lte82]

I’ve found the 4dof to work really well especially with Hornandy bullets.

Same here!

The one thing I’ve noticed is aerodynamic jump is overstated though, even more so than AB. If you’re truing up AFF in less than 10 mph wind I’ve had better luck setting wind to 0.

 

[Mudmarine]

Report back on what you find out.

 

[Ledzep]

There is an axial form factor on the 4DOF app, also. I'm not intimately familiar with the Kestrel version yet, but I would think it would be present there, as well.

 

[Dthomas3523]

There is an axial form factor on the 4DOF app, also. I'm not intimately familiar with the Kestrel version yet, but I would think it would be present there, as well.

He has the kestrel elite with AB, not the 4dof kestrel.

 

[Ledzep]

Ahh gotcha.. yeah then check out the axial form factor on the 4DOF app. Muzzle brakes and suppressors can induce some initial yaw effects that increase drag. Moral of the story is 2 different rifles can shoot the exact same bullet from the same lot and have slightly different CD curves depending on muzzle exit conditions, rifling, bore condition, etc.. etc... and that's what the axial form factor is for if you have verified good MV and scope over bore input.

 

[Swoodhouse19]

When you make the two separate curves...DO you adjust BC until you match your real world data or fudge with velocity. ( I apologize if this is a silly question, I do not shoot past 1000 often)

 

[Dthomas3523]

When you make the two separate curves...DO you adjust BC until you match your real world data or fudge with velocity. ( I apologize if this is a silly question, I do not shoot past 1000 often)

Typically you donthe BC at distance first. Then *if* the MV needs to be tweaked for closer distance, you will.

For a separate curve past 1k, it’s mainky going to be BC. Or DSF with kestrel.

And if you’re using custom curve, you don’t have the option of using B.C. so it’s MV and DSF only.


Basically, the answe is: you do whatever it takes to make it line up. That could be a custom curve with MV/DSF or a g7 with BC/MV.

 

[Swoodhouse19]

Thank you sir.

 

[Clearlight]

Agreed with truing if you have a chance. Does the AB account for aerodynamic jump like the 4DOF program? That could be the difference.

AB accounts for aero jump. OP, if possible if there’s a stage or two before the 1200 target, ask
spotters to confirm your elevation solutions on targets at shorter range first. You may have to
tweak velocity slightly to get both solvers to line up with actual drop. Unfortunately real world
data from your barrel/rifle/shooter is necessary to true solutions a lot of the time.

I’ve found that with my rifles and the way my LabRadar is setup, I often need to drop a few fps
in the solver from what the LabRadar is telling me. Could be a number of things like barrel
engraving or radar setup, but it’s not uncommmon to need to tweak velocity supplied by any
chrono regardless of type.

 

[Ledzep]

I leave known quantities what they are. If you are confident with MV (at least 20 rounds average on Magnetospeed or Labradar), I would mess with form factor or BC. Sight over bore is a given-- it is what it is. MV can change day to day with powder temp changes, but typically not very much with the temp stable powders we use.

 

[Dthomas3523]

I leave known quantities what they are. If you are confident with MV (at least 20 rounds average on Magnetospeed or Labradar), I would mess with form factor or BC. Sight over bore is a given-- it is what it is. MV can change day to day with powder temp changes, but typically not very much with the temp stable powders we use.

Unfortunately, even though known factors are known.....sometimes they are the only factors we can change.

Perfect world, you wouldn’t change your known velocity.

But if for whatever reason, say the calculator is off by .2 or .3 at 5 or 600, no amount of B.C. adjusting will line it up without totally wrecking your >600 dope.


I make MV the last thing I tweak (unless using custom curves), but sometimes you have to let the software do its thing to line up.

People are getting too OCD with this “but my chrono says this, so it has to be this.” Sometimes there’s something in the software we would need to change to make this velocity work, but we can’t get to that particular item inside the software. So the only thing we had a choice to change is the known.