This is my last post in a series on using mil-dots for ranging distance, leading a moving target, and adjusting for wind. I’ve focused on simple ways to make adjustments while skipping the complex math you will find all over the internet on other sites. My goal is to present easier methods that are memorable and accurate enough for use on your next deer hunt even if you haven’t thought about them for a while. Like my previous two posts, we will focus on distances out to 300 yards.
Before we get started, you do need to know that a bullet’s ballistic coefficient plays a significant role in how much the wind affects its movement. The higher the ballistic coefficient, the less wind impacts the bullets trajectory. In this post, I’m using a .308 Winchester 168-grain bullet as the example. The wind tables will be different for a .223 and change slightly for a lighter .308 bullet, like the common 150 grain. You can experiment with the calculator referenced at the end of this post to come up with your own simple adjustment for the specific cartridge you use. As I lead you through the steps of doing that in this post, you will be able to duplicate it for other cartridges.
Doping the wind, as many call it, is important at distances beyond 100 yards, and especially beyond 400 yards, because bullet velocity slows to the point where wind has greater affect. Look at the table on the left to see the effect of a 10 mph crosswind on a 168-grain, .308 Winchester bullet and the table on the right to see the effect of a 20 mph crosswind. As you can see, a bullet is moves off target 10″+ per 100 yards in a 10 mph crosswind after 500 yards!
Tables showing corrections for a 168 grain, .30 caliber bullet in 10 and 20 mph crosswinds. Click here to see the complete ballistics table for the 10 mph wind and here to see it for the 20 mph wind. Remember from my first post on mil-dots that 1 mil equals 3.6″ at 100 yards, 7.2″ at 200 yards, 10.6″ at 300 yards, etc. Pay special attention to columns 2 and 3 to compare inches to mils. Elevation adjustments are not affected by wind.
Key takeaways from the tables above for the 168-grain, .308:
- Don’t worry about adjusting for wind under 100 yards.
- A 10 mph wind requires less than a 1 mil-dot adjustment out to 400 yards.
- A 20 mph wind requires double the adjustment of a 10 mph wind. This is the case for all bullets.
- Don’t worry about adjusting for 5 mph wind out to 200 yards because the adjustment is half that for a 10 mph wind. At 300 yards, a 5 mph wind moves a .30-caliber bullet about 3.5″, that’s 1/3 of a mil or half the adjustment of a 10 mph wind.
A 10 mph wind is a great reference point. Get comfortable reading signs for a 10 mph wind. A 10 mph wind causes twigs and leaves to be in constant motion, dry leaves to move along the ground, and flags to extend out. Try to remember how a 10 mph wind feels against your face.
You can see and print a table describing visible signs of wind speed here. However, before you tuck that table in your jacket pocket, remember my goal is to make reading and adjusting for wind simple. It would be difficult for me to remember all of the visual cues for wind speed unless I used them weekly, so I’m going to focus on one wind speed for distances out to 300 yards that is relatively easy to remember and common: 10 mph.
One key takeaway from the table above is this: since it is unlikely for you to see winds above 20 mph when target shooting or hunting, focus on learning how to read wind below 20 mph. A 20 mph wind moves large tree branches. If you can remember the visual signs of a 10 mph wind, you can easily convert that to adjust for estimated wind speeds of 5, 15, and 20 mph.
If you can feel wind on your face but visual signs indicate less than a 10 mph wind, estimate a 5 mph wind. Likewise, if signs indicate the wind is moving faster than 10 mph, go with 15 or 20 mph. Remember, out to 300 yards, a good guess is good enough. At 400 yards and beyond, you need to be more precise with wind speed measurement.
What if there are no trees around and there’s a shortage of visual markers? My first answer is to know what a 10 mph wind feels like on your face. Beyond that you can use mirage to gauge wind speed if conditions are right. Believe it or not (and I challenge you to take a scope outside and look at an object 100+ yards away in cold weather on a sunny day), mirage exists in cold temperatures when the sun is out, even when there is snow on the ground. If mirage is horizontal, wind speed is at least 10 mph. See below.
This short, 2-minute video provides a great summary of using mirage to gauge wind speed. I encourage you to watch it. You don’t need a focus knob as indicated in the video, but that makes reading mirage easier. I use a Bushnell Elite 3200 10×40 mil-dot scope with no focus knob to gauge distances and read mirage around my house.
Rules of thumb for using mirage to gauge wind speed. I like the simple classification of Slow, Medium, and Fast. You will find small variances on the Internet on reading mirage. Some say a horizontal mirage, like in the last picture above, indicates at 15 mph wind. Whether 10 or 15 mph, that’s not a big deal at distances less than 500 yards.
For shots of 300 yards and less, you should try to gauge wind speed at your position and at the target. Wind may be blowing at the target but not at your shooting location. In that case, don’t give a full value adjustment for the wind. It may be blowing at 5 mph at 100 yards and 15 mph at 300 yards. In that case, allow for a 10 mph wind. Reading and adjusting for wind is definitely an art requiring practice!
When adjusting for wind, use full value, half value, or no value
depending on the wind’s direction relative to you and your target.
Using the image above for reference, if you estimate the wind is blowing 10 mph from
1 o’clock, treat it as a 5 mph wind. That means no adjustment out to 200 yards using our simple system. If you estimate a 10 mph wind from 9 o’clock, treat it as a 10 mph wind. If you estimate a 10 mph wind at your 6 o’clock, don’t worry about it since wind from that direction will not cause the bullet to move left or right.
Simple System for Wind Adjustments
- Don’t adjust for wind under 100 yards unless you’re shooting .22LR.
- Know the visual signs and physical cues of a 10 mph wind.
- Realizing that winds above 20 mph are unlikely, estimate wind speed at 0, 5, 10, or 20 mph.
- For a 168-grain .308, a 10 mph wind requires a 1/2 mil adjustment from 100-300 yards. (Use the calculator below to determine the mil adjustment for your cartridge between 100-300 yards in a 10 mph wind.)
- Halve this adjustment to 1/4 mil from 200-300 yards for a 5 mph wind.
- Double the adjustment to 1 mil for a 20 mph wind from 100-300 yards.
You can get as complicated as you want when it comes to reading wind and adjusting for it. Unless you read wind and shoot in windy conditions on a regular basis, you are better off using this simple system versus guessing or making no adjustments at all. When you are outside and the wind is blowing, take advantage of the situation to learn more about the wind!
If you are interested in wind correction for other calibers, I encourage you to use ShootersCalculator.com. In my opinion, it offers the best combination of simplicity and versatility compared to other online ballistics calculators I’ve used. Normally you can find muzzle velocity and ballistic coefficient values on your box of ammunition. If not, use the free Swarovski ballistics app I discussed in an earlier post. One important note about muzzle velocities listed on boxes of ammunition: they are typically measured using longer barrels in the 24-26″ range. If you are shooting a carbine with a 16″ barrel, your muzzle velocity will be about 200 ft/s less, and you need to adjust for it in the calculator.
Obviously adjustments will be different for common calibers like .223 Remington, .243 Winchester, .30-06 Springfield, and .270 Winchester. Muzzle velocity, ballistic coefficient, and bullet weight all contribute significantly to the path of a bullet’s flight in a crosswind.
I hope you enjoyed our 3 lessons on the use of mil-dots. Now it’s time to take what you know and put it into practice at the range.
On a final note, if you have money to spend and like gadgets, you can buy an instrument to measure wind speed, temperature, and barometric pressure which are inputs for more sophisticated ballistics calculators. The go-to brand is Kestrel. This YouTube video shows the $150 Kestrel 2500NV in action.