Asking for a friend. We are starting to shoot "farther range" (by no means long range, but 600 so far, looking to go to 1000 in the near future).

The question is

When calculating wing readings, does a 45 degree wind calculate as a 1/2 value or a 3/4 value? This would be a headwind from 10:30 or 1:30. from googling, results seem conflicting.

Thanks!

Yep, lots of tables with different values and approximations, both on the webz and in print.

I've found that a 45 degree wind will be in the 2/3 to 3/4 value, probably closer to 3/4. Definitely more than 1/2 value. To be honest, I find it difficult to come up with an exact metric in the field. Ultimately we need feedback from the bullet's impact to see the real wind effect. Unfortunately, by the time we figure that out, the wind likely has changed.

quote:

Originally posted by fritz:
Yep, lots of tables with different values and approximations, both on the webz and in print.

I've found that a 45 degree wind will be in the 2/3 to 3/4 value, probably closer to 3/4. Definitely more than 1/2 value. To be honest, I find it difficult to come up with an exact metric in the field. Ultimately we need feedback from the bullet's impact to see the real wind effect. Unfortunately, by the time we figure that out, the wind likely has changed.

that makes sense. So as a general rule of thumb, so you start with a 2/3 or 3/4 valuation? Like what would you plug in your calculator for a first round impact? Knowing the wind was at a 45* angle.

I'm not really a calculator guy in the field. Understand that the game of steel targets that I play doesn't require gnat's ass precision. We have targets that are usually in the 1-3 MOA wide ballpark, many are probably 2-ish MOA wide. I don't get "X-ring" versus "9-ring" scores, just a hit or a miss.

In the past few matches I've attended I didn't have time to plug data into a calculator. I pre-print elevation dope cards based on Density Altitude, and list the 10 mph wind drift for the given distance intervals -- usually 25 yards.

So let's say I have a 600 yard target, using 7000' Density Altitude, with my 6.5CM. My dope card says a 10 mph cross wind (from either 9 o'clock or 3 o'clock) gives me 2.7 MOA of drift. Furthermore, there's a 12 mph wind from my 4:30. The 12 mph wind increases the 2.7 MOA drift by 20% to 3.2 MOA. The 4:30 wind reduces the 3.2 MOA (using 75%) to 2.4 MOA. That's more math than I generally have time for. In these conditions I'd probably say the relative wind vector angle offsets the wind speed, and I'd ballpark the correct hold at 2.5 to 2.75 MOA wind. This assumes I have the time to really calculate numbers.

My scopes have windage adjustment values in 1/4 MOA increments. My scope reticles have 1 MOA windage hash marks. Maybe once a match I dial windage, the rest of the time I hold wind. With a 1 MOA reticle, trying to determine the difference between a 2.5 and 2.75 hold is ludicrous. So I may wing it with something a little less than 3 MOA (assuming my head is out of my backside), break the shot, and hope the wind hasn't changed. On a 2 MOA wide piece of steel, if I guessed the 12 mph wind and its direction reasonably well, the RO will say "impact".

Now if you're shooting for score on paper, and you have the time to make calculations, then I recommend less "winging it".

A wind from 45 degrees with respect to the line of sight to the target will have 0.71 of the effect of a wind at 90° to the line of sight. That’s pretty close to 3/4, which is why the (correct) wind value charts say three-quarters. The precise value for any wind is the trigonometric sine (sin) of the angle. That’s why the value for 90° (3 or 9 o’clock) is 1 and the value for 0° (12 o’clock) or 180° (6 o’clock) is zero.

Many books on long distance shooting have the above information wrong. The most common error is to assume that a wind from 45° is one-half the value of a 90° wind. Actually a 30° wind (1, 5, 7, or 11 o’clock) has half the effect or value of a 90° wind.

If, BTW, anyone doubts the information in my above post, I invite you to visit the JBM ballistics calculator site. Any values can be entered for the fields except the “Wind Angle” about half way down. The default angle should be 90°; if not, enter that. Then click on “Calculate” at the bottom of the page. That will then take you to the next page of the site where the results are displayed. Look at the “Windage” column under “Calculated Table.” Pick a distance of at least a couple of hundred yards and note the value there.

After noting the wind drift value for the distance you select, click the back arrow to go to the original data entry form. Go to Wind Angle again and change the figure from 90 to 30° and calculate. Look at the same column and distance, and you’ll see that the windage figure is half of what it was at 90°. If you set the Wind Angle to 45° and calculate, you’ll see that the Windage value is about 0.7 of the 90° figure.
Note that the program rounds the result figures to the nearest 0.1 and therefore the percentage relationships of the figures may not be fractionally exact.