DocUSMCRetired
Well-Known Member
Applied Ballistics Wind Hack!
Drop/Wind Number = Wind Correction
Wind Number IS NOT Wind Speed. Formula calculates for 10mph Wind that you can scale.
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, etc. 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 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. It works the same for MILS and MOA because its an angular conversion.
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.
Example 2: You are shooting a .264 Berger Bullets 140 grain Target Hybrid with a G7 BC of 0.311, and your drop is 7.22 mils at 1000 yards. For a G7 BC of 0.311 your 'wind number' is 2+3=5. So your 10mph wind deflection is 7.22/5 = 1.4. Actual 10mph wind correction is 1.8. This gets you to less than 1/2 a mil of the actual wind value with mental math in a matter of seconds!
Some caveats:
1. Because this requires the BC in the formula, its very important that the BC be accurate such as the tested and proven BCs from Applied Ballistics.
2. Your drop number has to be from a 100 yard zero.
3. This wind hack is most accurate for supersonic flight.
4. Within supersonic range, accuracy is typically better than +/-6".
5. You can easily scale the 10 mph crosswind deflection by the actual wind speed.
6. Wind direction has to be scaled by the cosine of the angle.
7. SG Needs to be 1.5 or higher. An SG (Gyroscopic Stability) Factor below 1.5 can reduce your BC by 3% for every 0.1 SG.
8. Do not include Horizontal Coriolis when considering accuracy of the formula, this is purely a wind calculation.
9. Do not include Spin Drift when considering accuracy of formula, twist rates affect the spin drift different, and this is purely a wind calculation. Fast twist barrels might cause a larger discrepancy.
10. Always remember an Accurate Muzzle Velocity is an important part of any firing solution (In this case Drop).
This is just one of the many things shooters learn during the 2 days of advanced ballistics instruction at the Applied Ballistics LLC Seminars. To learn more, and get a seat at our final class of the 2016 season Applied Ballistics Seminar #4 - Fort Bragg, NC check out here: Applied Ballistics Seminars - 2016 - Applied Ballistics, LLC Give the AB wind hack a try to see how it works with your ballistics, and remember its designed to get you a solution in a pinch!
Drop/Wind Number = Wind Correction
Wind Number IS NOT Wind Speed. Formula calculates for 10mph Wind that you can scale.
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, etc. 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 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. It works the same for MILS and MOA because its an angular conversion.
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.
Example 2: You are shooting a .264 Berger Bullets 140 grain Target Hybrid with a G7 BC of 0.311, and your drop is 7.22 mils at 1000 yards. For a G7 BC of 0.311 your 'wind number' is 2+3=5. So your 10mph wind deflection is 7.22/5 = 1.4. Actual 10mph wind correction is 1.8. This gets you to less than 1/2 a mil of the actual wind value with mental math in a matter of seconds!
Some caveats:
1. Because this requires the BC in the formula, its very important that the BC be accurate such as the tested and proven BCs from Applied Ballistics.
2. Your drop number has to be from a 100 yard zero.
3. This wind hack is most accurate for supersonic flight.
4. Within supersonic range, accuracy is typically better than +/-6".
5. You can easily scale the 10 mph crosswind deflection by the actual wind speed.
6. Wind direction has to be scaled by the cosine of the angle.
7. SG Needs to be 1.5 or higher. An SG (Gyroscopic Stability) Factor below 1.5 can reduce your BC by 3% for every 0.1 SG.
8. Do not include Horizontal Coriolis when considering accuracy of the formula, this is purely a wind calculation.
9. Do not include Spin Drift when considering accuracy of formula, twist rates affect the spin drift different, and this is purely a wind calculation. Fast twist barrels might cause a larger discrepancy.
10. Always remember an Accurate Muzzle Velocity is an important part of any firing solution (In this case Drop).
This is just one of the many things shooters learn during the 2 days of advanced ballistics instruction at the Applied Ballistics LLC Seminars. To learn more, and get a seat at our final class of the 2016 season Applied Ballistics Seminar #4 - Fort Bragg, NC check out here: Applied Ballistics Seminars - 2016 - Applied Ballistics, LLC Give the AB wind hack a try to see how it works with your ballistics, and remember its designed to get you a solution in a pinch!
