Calculating Wind Drift (When You Don’t Have A Working Device)
Applied Ballistics Wind Hack
Any long range shooter knows that wind is our ultimate nemesis. The best ways of overcoming wind are to measure what we can and use computers to calculate deflection. The Applied Ballistics Kestrel is a great tool for this. As good as our tools may be, we don’t always have them at our fingertips, or they break, batteries go dead, and so on. In these cases, it’s nice to have a simple way of estimating wind based on known variables. There are numerous wind formulas of various complexity.
The Applied Ballistics (AB) Wind Hack is about the simplest way to get a rough wind solution. Here it is: You simply add 2 to the first digit of your G7 BC, and divide your drop by this number to get the 10 mph crosswind deflection. For example, suppose you’re shooting a .308 caliber 175-grain bullet with a G7 BC of 0.260 at 1000 yards, and your drop is 37 MOA. For a G7 BC of 0.260, your “wind number” is 2+2=4. So your 10 mph wind deflection is your drop (37 MOA) divided by your “wind number” (4) = 9.25 MOA. This is really close to the actual 9.37 MOA calculated by the ballistic software.
WIND HACK Formula
10 mph Cross Wind Deflection = Drop (in MOA) divided by (G7 BC 1st Digit + 2)
Give the AB wind hack a try to see how it works with your ballistics!
Some Caveats: Your drop number has to be from a 100-yard zero. This wind hack is most accurate for supersonic flight. Within supersonic range, accuracy is typically better than +/-6″. You can easily scale the 10 mph crosswind deflection by the actual wind speed. Wind direction has to be scaled by the cosine of the angle.
Similar Posts:
- Wind Hack — Estimate Crosswind Deflection Without a Meter
- Estimate Crosswind Deflection WITHOUT a Meter — WIND HACK
- The Wind Hack — Quick Way to Calculate Crosswind Deflection
- Brain Teaser: Do You Know the Rule of the Square?
- Crosswind Weighting Factor Explained by Bryan Litz
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Tags: Applied Ballistics, Bryan Litz, Crosswind, Deflection, Estimation, Kestrel, Wind Hack, Wind Reading
Don’t forget to factor in aerodynamic reflection wind formula as taught by Todd Hodnett. To get the complete details listen to Precision Rifle podcast episode 46. Wind from the left will cause your Bullets to drop down .125 @ 100 yds. Wind from the right will cause the bullet to go up. This is to be added to your windage adjustment or horizontal adjustment.
This seems fine for 1000yd but wind drift and bullet drop is not a constant for all ranges.
At 1000 yds the division factor (drop/bc+2) ie 4 is correct.
However at 300 yds the factor is approximately 2 and at 700 yds it is approximately 3.
Bob,
Can you share the details of your example so we can consider it further?
There are some cases where the MOA error is high at shorter ranges, but the resulting inches of miss is usually less than 6″.
I admit there is some error in this approximation. It’s not intended to be perfect, but a simple, easy to remember guideline to get you close if you have nothing better to go by.
Good shooting,
-Bryan
Teach them to read a wind chart and mirage.
Brian
Using the Hornady online calculator in G7 mode with BC 0.26, 175 gn and 2800fps seems to confirm my comments.
I normally use a G1 model (Perjesa or Quickload which gives similar results and seems to work in practice for me at shorter ranges on smaller targets (< 400yds). I appreciate the ~4 factor it is only an approximation and will get you on the target at longer ranges.
Best regards
Bob
Bryan
Sorry for using Brian, UK spelling.
Bob
Bryan
Apologies for incorrect name spelling.
Used the UK version!
Bob