· Understanding the size of our target and what it means to us for wind calculations
· Knowing our margin for error
1. Finding our guns wind #:
a. First things first, we must calculate the muzzle velocity (MV) of our rifle by using a Magneto Speed (chrono-graph) or a lab radar (these are the most accurate methods of finding the rifles MV)
b. There are a few trains of thought on how to do this, I will only discuss the method I use and why, if you do something different that is perfectly fine, but I will keep it with just my method for simplicities sake.
i. The first test is a 10 – 12 round string (solely based off the number of engagements I will be executing in a competition stage). I conduct this with 5 seconds in between each shot, this is because typically I run my gun at this rate when I am running a stage or a training session, so it just makes sense to simulate the same shooting conditions to get the most accurate MV to how I will be running the weapon when it counts.
ii. The second test is 5 strings of 2 shots with 10 seconds in between, this is to see if there is much of a change between the strings, simulating that I am transitioning positions during a competition stage.
c. If you run your rifle chrono in a different method that is perfectly fine, do what you’re comfortable with and use that data, it doesn’t make sense to test it the way I do if you do not use your rifle the way I do, but I suggest you try to simulate as close as possible to how you will be shooting it so it gives you the most accurate numbers.
d. Once you’ve done this plug the data into your ballistic solver so you can prepare for the next step.
e. Once you have your ballistic solver updated with the data, you will need to turn off spin drift, and set your wind value to full (90 degrees or 270 degrees works perfect). Then start with a low wind speed (3-4 MPH) and set your range card increments to 100 yds (or meters if that what you shoot in).
f. Once that is done populate your range card and see what your wind correction is WITHOUT SPIN DRIFT (some solvers do not allow you to turn off spin drift, so hopefully it will have two wind columns, one for total wind and one for wind specifically, look at the one for specific wind corrections so spin drift is not added in to change your data).
g. I will use my guns data for the example (.308 @2714 FPS) I am looking for my wind correction to “equal” my range to target. IE: 100 yds = .1, 200 yds = .2, 300 yds = .3, 400 yds = .4, 500 yds = .5, and 600 yds = .6
h. To do this I will continue to add wind speed until these numbers match up, so for example it should look like this depicted below. I will round the number to the closest tenth, because they will not line up perfectly… normally (unless you have the perfect MV to make that happen, which I have never seen).
i. Once the numbers have lined up and everything is matching, we will have a solid understanding of our rifles wind number at this point.
2. Understanding the capabilities of our bullet:
a. For this example, I will be using the same example (.308 round @ 2714 = 4 MPH Wind #), this will keep everything consistent for the entirety of our processes here.
b. Going back to our chart we will see that after 600m (same for yards) the wind begins to affect the bullet more drastically. This is because the amount of retained velocity and energy has reduced to a point, this is specifically for the example round. Each round will be different depending on the variables surrounding it, so make sure to check your data even if you are using a .308 like the example, it can be different.
c. ANOTHER IMPORTANT NOTE, this number will potentially change depending on where you are shooting at as well, so check your Density Altitude/atmospherics to confirm they are correct and remember that anywhere you go to shoot you need to confirm that it is the same or has changed so you are thinking in the correct wind bracket.
3. Understanding the winds effect on our bullet:
a. This is a relatively simple concept, of understanding how far the bullet is being pushed horizontally by the wind. If you understand this, you can apply it to the next step quickly to maintain more accurate shots.
b. If we understand that .1 mil at 100 yds is equal to 1 cm and it is relative as distance grows so. 1cm = 100 yds, 2cm = 200yds, 3cm = 300yds then we can process how the bullet is traveling down range towards the target and where we should expect it to impact. For example, 300 yd target with 4 MPH full value wind without example round = .3 wind call which means we are compensating for 9 cm of movement. If we convert to inches to make it easier to track, then we know 9 / 2.54 = 3.54 inches. This is because there are 2.54 cm in 1 inch, so that’s our constant. To find how many inches. In the next step we will explain why inches is more relative to our process than cm’s.
4. Understanding size of the target and what it means for wind calculations:
a. Once we figured out wind #, understand how the adjustments work, and understand how many inches per click we are adjusting we can now begin to understand our target.
b. Regardless of the bullet the target itself gives us a large amount of information that is extremely important. SIZE, if the target is 10 inches wide that gives us our bracket. For a perfectly centered shot we have 5 inches left and right to play with. Every target size should be divided by 2 to give us left and right lateral limits for impacts. This can be converted into cm and mils relatively quickly by reverse math from the previous step.
c. EXAMPLE: (still using 300-yard target, 10-inch width) 5 inches x 2.54 (constant) = 12.7cm divide by 30 (range constant) gives us .42 mils from center to edge.
d. You can also do this by just milling the target and you should get approximately .8 mils edge to edge then divide by 2 to get .4 mils
e. This lets us know that if we had a 4 MPH full value wind at 300 yards, and we did not adjust .3 then we should hit approximately .1 from the edge of the target.
5. Knowing our margin for error:
a. Taking our examples from the previous sections, knowing that our target is 10 inches wide and that breaks down to .8 mils at 300 yards which means .4 mils from center to edge by halving our totals. We now know we have .4 mils for margins of error in wind calling.
b. Knowing our mil margin of error will also allow us to figure out our wind calling margin of error, by adjusting our wind speed in our ballistic calculator we can identify that it will take up to 6 MPH full value wind to push our round .4 mils at 300 yards and 7 MPH to push it .47 mils, which means that if we did not account for wind and we aimed perfectly center and broke a perfect shot on a 10 inch target, theoretically we will need more than 6 MPH to guarantee a miss at that distance.
c. BUT WHAT IS IMPORTANT TO UNDERSTAND, is that means we can that far off a wind call at that distance to miss that shot with good fundamentally sound shots taken at center. SO, to make this more understandable we will move to a 635-yard target, same size same wind.
d. 635-yard 10-inch target is .4 mil’s wide, so we have .2 mil’s left and right of center in margin of error. This means that a 1 MPH full value wind will push out round .15 mils, so we must be accurate within 1 MPH to effectively engage and hit the target.
e. Therefore, practicing wind calls is important because if we can effectively estimate down to within 2 MPH, we will have .33 mils of accuracy within our target width. Now that we understand how to break down our target size and convert it to mils/MPH margins of error we can effectively give ourselves the ability to make wind brackets to each target prior to engaging. This will be covered in a different post due to it having its own series of steps to build and prepare for engaging targets.