In this posting we’re going to discuss the proper terminology for wind calls. Newer shooters are often eager to get into learning the wind and there is some misinformation out there. As a result we have newer shooters using the wrong terms or incorrectly communicating with their spotter or the shooter they are spotting for. The goal of this article is going to be the proper communication and terminology to use when describing what we see happening with the wind. The idea is that by all using the right terms and communicating what we see based on the same set of ground rules that we can eliminate some of the errors between shooters when trying to help each other out with what’s happening down range.
Wind Call Guidelines
The first step to effective communication of wind calls is to establish some kind of baseline. A reference condition or model by which to judge what we see and what we want to communicate to others. That guideline is going to be what we refer to as a 10mph Full Value wind hold. Now what is that and why 10mph and not 5mph or 15mph or 1mph? Glad you asked. With all the various variables that have an effect upon a bullet in flight…the drift and adjustment needed to account for it aren’t linear. You can’t calculate an adjustment for 1mph and then multiply that by the wind speed, it doesn’t work. That is a significant fact of life for the aspiring precision marksman. Here’s what I mean.
The reason you can’t calculate wind at 1mph and then just multiply that value by 5 for a 5mph wind value or 20 for a 20mph wind value is because the effects of wind upon a bullet and the subsequent horizontal drift are not linear. The faster the wind is moving the more of an effect it has upon the projectile while it’s in flight. The reason we typically use a 10mph Full Value wind hold is because the differences between the actual effects of wind and what we get by doubling, halving, etc. our 10mph value are pretty close to what you actually get. We are talking about a field expedient method of coming up with a wind hold here. Obviously if you want the most accurate data the best way is to use a ballistics calculator and get a live reading on the spot.
Live Data -vs- Rule of Thumb
Tools like the Kestrel 4500 Applied Ballistics can take all the environmental factors into account on the spot and give you an accurate hold based on the distance, speed of the wind, and the angle of the shot and its relation to the source of the wind. However, we don’t always have access to a tool like this. Sometimes the battery dies. Sometimes its cold and the electronics get wonky. Sometimes you just don’t have time to punch all the data up and get a live result. Maybe the deer you are hunting is starting to move to where the shot will be obscured. Maybe you are participating in a rifle match and time is running short. Maybe you work in Law Enforcement or the Military and real life isn’t going to wait for you to use your handy toys.
Proper Wind Call Angles
We want to get in a habit of talking about the 10mph Full Value wind hold, and fractions of it. Some of the bad information out there has to do with that linear thinking we discussed earlier. There are a lot of older graphics floating around with improper labeling. The biggest culprit comes from the military field manuals that tell everyone that reads them that wind approaching the angle of fire at 45 degrees have a value that is half, or 50%, of what the full value wind angle actually is. The 90 Degree or Full Value wind has the greatest effect on the path of the projectile. Unfortunately this graphic isn’t correct.
The cosine of a 45 degree angle is actually 0.707, which is basically 71% of the 90 degree Full Value wind. So while everybody is assuming that the wind’s effect at 45 degrees has been halved from 90 degrees, its really actually almost three quarters of the 90 degree effect. This is where we get into looking at the proper terminology for making these wind calls. Since 71% is just a tick shy of 75% for the purposes of keeping everybody on the same page and the terminology simple, we’ll refer to this as three quarter value. That is a much closer representation of the true effect of wind at the 45 degree, or three quarter value, angle!
This means the true half value of your 10mph 90 Degree/Full Value wind call is going to be between 0 degree/No Value and your 45 Degree/Three Quarter Value angles. You can break out a calculator and protractor and dissect the winds angles into values as fine and precise as you please. When making my own field expedient wind calls, or communicating what I’ve seen or used to another shooter, I like to keep things simple. I refer to my wind calls as no value, half value, three quarter value, or full value. There are a few people that either don’t know, or perhaps use a different wind speed when making these calls. So I’ll specify if I’m asked about my wind hold, “Half of your 10mph Full Value,” to relate the amount of wind compensation I’ve built into my firing solution.
Wind Calls Translated Across Calibers
I’ll give credit where it’s due. I immediately saw the advantages to calling wind this way after talking to Ray Sanchez of Thunderbeast Arms Corporation. I was talking to Ray about some tips at the Train Up that TBAC was hosting prior to the 2012 Sniper’s Hide Cup. We were talking about how best to communicate wind calls to other shooters whether at a team competition or a buddy on a home range. Ray told me that he frequently shoots with Zak Smith and quite often they are shooting different rifles with different calibers. This is where the relevancy of a standard wind call comes into play.
If we all get into the habit of using 10mph Full Value wind as our standard, then references will translate across ranges, different calibers, projectiles, ballistic coefficients, you name it. I could be shooting a 308 Winchester next to a buddy who’s shooting a 338 Lapua Magnum and if done properly, we can communicate wind calls between each other that are relevant and meaningful despite the vast differences in ballistics and energy between the two calibers. If I’m having trouble hitting at a thousand yards with my 308 and I ask my buddy what he’s using for wind, he can give me a relevant answer.
If my buddy with the 338 Lapua Magnum is hitting easy and he tells me, “I’m using three quarters of my 10mph full value,” then I know to look at my own ballistic table to see what the correction for my 308 is for a 10mph Full Value wind. I then use three quarters of that value and unless the conditions have changed significantly, which is possible, I should make a hit using his wind call. The differences in ballistics are accounted for by using the different tables for the different rifles. Since he’s using 50% of a standard scenario, like 10mph Full Value wind, that becomes something of a unit free reference. 50% of my own 10mph Full Value will be different, but being the same percentage should yield the same result.
Wrapping Up Wind Call Communication
Remember the idea here is to utilize the proper terms and in a manner that facilitates proper and effective communication of what the wind is doing. Remember a wind at 45 degrees to the firing angle is not half value, that is a three quarter value. When referring to your wind calls, refer to them in a language that all of us speak. I will revisit this concept in future wind articles because this is the foundation for making wind calls. I’m working on another article about reading the wind and the 10mph Full Value Standard is a significant foundation for reading the wind and making proper wind calls.