Hornady 4dof windage question

[Cm308]

I have been noticing that a left to right wind is given a larger correction than a right to left wind with Hornady 4dof. Most specifically when comparing a 4-5 o'clock wind and a 7-8 o'clock wind.
Is this difference because of spin drift being added in? Or is there something else going on here?

 

[Cm308]

Pics

 

[_Windrider_]

I have been noticing that a left to right wind is given a larger correction than a right to left wind with Hornady 4dof. Most specifically when comparing a 4-5 o'clock wind and a 7-8 o'clock wind.
Is this difference because of spin drift being added in? Or is there something else going on here?

I would say yes it’s SD (if you believe in that sort of thing).

 

[Cm308]

I normally use strelock and I don't see This variation. I have just recently started playing around with the 4 dof and am wanting to understand what's going on here.
I need to play with it more and figure out if I can turn SD off.

 

[GrandpaDeadLegs]

Another super tiny thing people calculate is cross wind or aerodynamic jump - bullets spinning into the wind can climb a little (fall less quickly) or something like that, since most of us have right hand twist barrels it will probably keep giving different results for opposite wind directions. I was playing around and noticed the same thing but various podcasts had prepared me for it...

 

[ubettcha]

r to l will also have a shorter shoot to distance the tighter you twist the bullet

 

[pell1203]

If you want to view calculation differences with and without spindrift and Coriolis included just turn “Earth Based Effects” on or off.

 

[Cm308]

Thanks Pell I didn't know that

 

[Cm308]

Tried turning earth based effects off and on, makes no difference. Still getting a full moa difference based on whether wind comes from left or right. I'm not understanding why???

 

[pell1203]

Tried turning earth based effects off and on, makes no difference. Still getting a full moa difference based on whether wind comes from left or right. I'm not understanding why???

Cm308, is the full MOA difference you are referring to in the elevation? If so, I believe what you are seeing is the Hornady 4DOF program accounting for aerodynamic jump as previously mentioned by GrandpaDeadLegs a few posts above this one.

It might be easier to verify this if the Hornady 4DOF allowed you to input a negative number for a left hand twist barrel but it only works for RH twist values at this time.

 

[Slo cat]

I love playing with their BC. I see that there is a negative aerodynamic jump with the wind a 270 degrees, and a positive AJ with the wind a 90 degrees. But nowhere do I see where you can imput a right or left hand twist for your barrel. Edit: just read again the above post regarding the AJ working only for RH twist. Doh.

 

[pell1203]

I love playing with their BC. I see that there is a negative aerodynamic jump with the wind a 270 degrees, and a positive AJ with the wind a 90 degrees. But nowhere do I see where you can imput a right or left hand twist for your barrel. Edit: just read again the above post regarding the AJ working only for RH twist. Doh.

So, is this why they call you Slo cat?

 

[Cm308]

Cm308, is the full MOA difference you are referring to in the elevation? If so, I believe what you are seeing is the Hornady 4DOF program accounting for aerodynamic jump as previously mentioned by GrandpaDeadLegs a few posts above this one.

It might be easier to verify this if the Hornady 4DOF allowed you to input a negative number for a left hand twist barrel but it only works for RH twist values at this time.

Not elevation, windage

 

[pell1203]

Cm308, don't know what bullet/ballistic data you are using but the windage change you see is within reason for twitchy winds from the directions you specify in your earlier screenshots.

Look for recent "wind rose" discussion threads here on the forum to better understand how significant of an impact even slight wind shifts left and right blowing from behind or towards you can have on your shooting solution. These kinds of winds are oftentimes the most difficult winds to shoot in.

Start by reading this Wind Angle thread. Lots of valuable info here!

 

[Cm308]

Sorry Pell I think you just don't understand what I'm saying.

The exact same wind mph from the left is given a correction of 1moa more than if the exact same wind is coming from the exact opposite angle from the right.

That's what doesn't make sense to me, not wind values based on direction.

 

[LastShot300]

Sorry Pell I think you just don't understand what I'm saying.

The exact same wind mph from the left is given a correction of 1moa more than if the exact same wind is coming from the exact opposite angle from the right.

That's what doesn't make sense to me, not wind values based on direction.

Odd to say the least or just plain wrong what the software is doing.

 

[Slo cat]

So, is this why they call you Slo cat?

Maybe I'm just a cool cat from San Luis Obispo. Or I like cats. Or I like to lay back on the couch with my TV remote and a beer.

 

[TomH Tx]

So, just for grins I ran 600 yard scenarios in Strelok, and Trasol, with 5mph winds at 8:00 and 4:00. Strelok showed NO difference between having the winds from 8 or 4. Trasol required .2mil more if the winds were at 8, BUT, even with NO wind Trasol was calling for .1mil left. So, then I went back into 4DOF, and at 600 yards, 4DOF is calling for .1mil left with NO wind.

 

[pell1203]

A bullet shot out of a right hand twist barrel is spinning at a high rate and will tend to drift to the right as it travels downrange. Some ballistic solvers take this into account when providing a solution while others don’t. Some to a greater degree than others.

Someone else can explain the physics behind it in greater detail if they wish but the concept is similar to what happens when a pitcher puts a spin on a ball to make it curve or sink.

 

[LastShot300]

So, just for grins I ran 600 yard scenarios in Strelok, and Trasol, with 5mph winds at 8:00 and 4:00. Strelok showed NO difference between having the winds from 8 or 4. Trasol required .2mil more if the winds were at 8, BUT, even with NO wind Trasol was calling for .1mil left. So, then I went back into 4DOF, and at 600 yards, 4DOF is calling for .1mil left with NO wind.

You sure AJ and SD were off?

 

[CJWhiskus]

I don't think you can turn spin drift off in 4dof. However, look at the table generated. The second column is Total Windage and includes spin drift. Scroll to the right. You will see a column that says just Wind Drift and right next to it a column that says Spin Drift. The Wind Drift column is wind drift only and should say exactly the same thing if you switch wind to either side. The value shown on the main screen does include wind drift and I can find no way to change it.