The Quick Wind Factor: a wind correction you make from memory, and how accurate it is.
Every rifle has its own reference wind.
With that wind the correction is 0.3 mil at 300 m, 0.5 at 500, 0.7 at 700.
With a .308 it stays within a few hundredths of a mil out to 700 meters.
In the field there is no time for math. The Quick Wind Factor is a number for your rifle that turns the wind into a correction you can make from memory.
For every rifle and load there is a "reference" wind at which the correction in mil is simply the range divided by a thousand: 0.3 mil at 300 meters, 0.5 at 500, 0.7 at 700. If the wind is twice as strong, the correction doubles.
With our .308 the reference wind is 5.5 km/h at 90°. Here is the rule compared with the full calculation:
| Range | Rule (mil) | Full calculation (mil) |
|---|---|---|
| 100 m | 0.10 | 0.08 |
| 300 m | 0.30 | 0.25 |
| 500 m | 0.50 | 0.46 |
| 700 m | 0.70 | 0.72 |
Out to 700 meters the rule stays within a few hundredths of a mil of the full calculation. Beyond that the gap grows: this is why the app always tells you the range up to which your number is valid.
The reference wind changes with caliber, bullet and velocity. The app calculates it for your profile, tells you the range up to which it is valid, and shows it in Tools, together with the Speed Drop Factor for drop.
