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Author Topic: Ballistics: Bullet Drop vs Wind  (Read 724 times)

Offline OltHunter

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Ballistics: Bullet Drop vs Wind
« on: October 14, 2020, 10:31:49 AM »
Been working some things up in the Hornady app to get my dope disk finished, and came across a question on ballistics with regard to bullet drop and the wind speed and direction:

According to the app:

With 0 wind, at 400 yards I have a drop of 4.25 MOA.

With a 20 MPH cross wind from 3 o'clock that changes to 2.75 MOA.

With a 20 MPH cross wind from 9 o'clock that changes to 5.75 MOA.

That's a pretty significant difference, does that seem right if I'm sighted in with 0 wind?  Or is there something going on with the Hornady app?  I haven't seen the wind affect bullet drop that much using other calculators.

Right twisted barrel 8, BC of .62, velocity of 2650 fps.

I get the barrel twist wind direction difference, but didn't think it would be that significant to throw off the drop by 6-7" each direction.

Thanks.

Offline birddogdad

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Re: Ballistics: Bullet Drop vs Wind
« Reply #1 on: October 14, 2020, 10:36:04 AM »
try a different app..
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Offline fishngamereaper

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Re: Ballistics: Bullet Drop vs Wind
« Reply #2 on: October 14, 2020, 10:40:28 AM »
I've heard that app is jacked up. Never tried it myself though.

Bullet drop is bullet drop only really affected by angle.

Wind holds don't affect bullet drop.  Unless your wind is a side hill wind on a steep incline or decline.

And if it's the 4dof app they are trying to correct for vertical shift of the bullet depending on wind direction, which in my 25 years of long range shooting I've never seen as a major issue.
« Last Edit: October 14, 2020, 10:54:23 AM by fishngamereaper »

Offline OltHunter

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Re: Ballistics: Bullet Drop vs Wind
« Reply #3 on: October 14, 2020, 10:51:59 AM »
Thanks all for the replies, that confirmed my suspicions! 

Offline CoryTDF

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Re: Ballistics: Bullet Drop vs Wind
« Reply #4 on: October 14, 2020, 11:28:43 AM »
Cleary this is a calculation for road hunting. The first shot is from the car at a stop. The subsequent shots are at speeds recorded as the vehicle careens down the hill while rolling. You guys don't use that app? :chuckle:
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Offline birddogdad

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Re: Ballistics: Bullet Drop vs Wind
« Reply #5 on: October 14, 2020, 11:57:45 AM »
I've heard that app is jacked up. Never tried it myself though.

Bullet drop is bullet drop only really affected by angle.

Wind holds don't affect bullet drop.  Unless your wind is a side hill wind on a steep incline or decline.

And if it's the 4dof app they are trying to correct for vertical shift of the bullet depending on wind direction, which in my 25 years of long range shooting I've never seen as a major issue.

i use shooter app and i like it pretty well!
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Offline Bill W

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Re: Ballistics: Bullet Drop vs Wind
« Reply #6 on: October 14, 2020, 12:08:32 PM »
wind direction does affect bullet drop.  It's a known thing to benchrest shooters.

Offline Stein

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Re: Ballistics: Bullet Drop vs Wind
« Reply #7 on: October 14, 2020, 12:22:00 PM »
Well, if you are adjusting for wind then the bullet has a longer path to target than if you are not adjusting (no wind).  A longer path means the bullet slows more and as a result is pulled to earth more.  That part is relatively easy to understand, just think of an extreme example in that you have to shoot 45 degrees to the left of the target.  In that case, the bullet will take a very long arcing path to the target and get there later (thus lower) than one shot directly at it with no wind. 

The rotation of the bullet and earth are a bit more complex.  Additionally, the wind is almost never exactly flat and exactly perpendicular to the bullet the whole path so there are additional incremental pushes up or down as well as slowing the bullet or speeding it up.

How much?  I have no idea, that's why I bought an app.


Offline Stein

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Re: Ballistics: Bullet Drop vs Wind
« Reply #9 on: October 14, 2020, 12:30:21 PM »
The app I use shows no difference for 20 mph wind at 90 degrees or 270 degrees at 400 yards.  It does show 0.1" difference for a tailwind.  I have no idea if that is accurate or what calculation it is doing and what variables it incorporates.

Offline jasnt

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Re: Ballistics: Bullet Drop vs Wind
« Reply #10 on: October 14, 2020, 12:48:30 PM »
AB shows 6.4 for 9 o’clock wing and 4.8 for 3 o’clock 20mph for my 300wm    For right twist barrel wind from right pushes bullet left and up, and down and right for left wind.   Has todo with spin rate.  Seen it many times. 
« Last Edit: October 14, 2020, 02:35:22 PM by jasnt »
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Offline Magnum_Willys

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Re: Ballistics: Bullet Drop vs Wind
« Reply #11 on: October 14, 2020, 01:41:30 PM »
 :yeah:
Think curveball -  rotation against wind creates denser air below bullet pushing it up against gravities greater force.   

Offline kbrowne14

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Re: Ballistics: Bullet Drop vs Wind
« Reply #12 on: October 21, 2020, 08:28:43 PM »
Aerodynamic jump. This is Bryan Litz's description of this factor: "Aerodynamic jump is what causes groups to slant when shot in varying wind conditions. ... When the bullet yaws to the side, gyroscopic action causes it to nose up or down by a small amount depending on the wind direction.

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Offline Alchase

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Re: Ballistics: Bullet Drop vs Wind
« Reply #13 on: October 22, 2020, 04:58:44 PM »
AB shows 6.4 for 9 o’clock wing and 4.8 for 3 o’clock 20mph for my 300wm    For right twist barrel wind from right pushes bullet left and up, and down and right for left wind.   Has todo with spin rate.  Seen it many times. 

Wouldn't it be more correct to say Right twist barrel wind pushes bullet left, and not down as much.
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Offline jasnt

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Re: Ballistics: Bullet Drop vs Wind
« Reply #14 on: October 22, 2020, 07:37:10 PM »
AB shows 6.4 for 9 o’clock wing and 4.8 for 3 o’clock 20mph for my 300wm    For right twist barrel wind from right pushes bullet left and up, and down and right for left wind.   Has todo with spin rate.  Seen it many times. 

Wouldn't it be more correct to say Right twist barrel wind pushes bullet left, and not down as much.
it does not push bullet up or down as much as left or right but it does move it enough to need to adjust elevation.  Enough to make over 6” different at 400 yards.  Granted that’s a 20mph wind but it does matter.    Brings a lot of truth to the ol saying garbage in garbage out.      This is why I love shooting in the crazy wind days.  It teaches you so much. 
243Round ct. 142
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The commission shall attempt to maximize the public recreational game fishing and hunting opportunities of all citizens, including juvenile, disabled, and senior citizens.
https://apps.leg.wa.gov/RCW/default.aspx?cite=77.04.012

 


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