Being that we live on a sphere, that orbits the sun and spins on an axis, I can't imagine there would ever be no wind. There is almost always the anomaly, but even if it's 1 mph and you can't feel it, it's still there. A 1 mph wind at 1000 yards will move a .308 10 inches. My point being, I always calculate for at least a 1 or 2 mph wind. If it seams like there's no wind, light a match and hold it up, you will see the flame flickering in the wind.
Using the methods that I talked about in part 1, I will estimate a minimum wind reading first. Lets say I have a 1000 yard target, with light, 10 mph gusts of wind from our 3 O'clock. And sometimes I can't feel the wind at all. Looking at my time of flight, it takes about 1.67 sec for my bullet to reach the target at 1000 yards. So, I would estimate that the wind gusts don't die down longer than 1.67 sec. Meaning, my minimum wind would be probably 2 mph for less than 1.67 sec so I'll use 3 mph as a minimum. If I use the wind formula;
Minimum wind
10 x 3 ÷ 11 = 2.72 moa, or ÷ 3.5 = .77 mils.
Maximum wind
10 x 10 ÷ 11 = 9.09 moa, or 2.6 mils
After running through my full firing solution, I know I will hold a minimum of .77 mils for wind. It is almost always recommended to hold for wind and I agree. It can and will change very quickly. However, with this method I like to dial in my minimum wind. I do this so I can use the center of my reticle as a reference and at max wind I will hold 1.83 mils. Essentially, giving one reference point instead of two. This stops me from having to remember two points of aim from my crosshair. I use this this method when I have no spotter and I'm calling my own wind.
Another method I use is to hold at the edge of the target. I normally use this with a combination of the method we spoke of earlier. It also helps with hit probability. As the wind picks up, without running a new calculation, I know if I hold far right on the target I have a high probability of getting a hit. An example; same as above, I have dialed in .77 mils on my scope to adjust for minimum wind. If I have minimum wind and aim center on a 20 in target at 1000 yards, I have a 10 in margin of error. However, if I aim to the far right I have just double my error margin. I now have a full 20 inches.
Lets do a little math. Do you remember our ranging formula?
Target size in inches x 27.77 ÷ number of mils in scope = distance in yards
We know the target is 1000 yards away and is 20 inches wide.
20 x 27.77 ÷ .55 = 1009 yards
Our target is .55 mils wide and our wind can be upto a 1.8 mil hold. So why not hold right of center? If the wind dies down you are still within you margin of error hitting the target at the right edge. If it picks up, you have doubled your margin of error and are more likely to make a hit. If you miss, then you would have missed anyway because you were holding center and only had a error margin of .275 mils.
If you see that the wind has died down aim to the right side of the target if the wind is near max hold the 1.8 mil mark on the left side of the target. If the wind is some where in the middle 5 - 7 mph hold .9 mil mark dead center. .9 mils is half way between your minimum and maximum wind call. Below are a few pictures illustrating the different holds.
Also, when calculating wind from an angle we talked about 3 and 9 O'clock being full value, and 2, 4, 8, and 10 O'clock being 3/4 value (dividing by .75). Most people stop there and call an angular wind 3/4 value. But what about 1, 5, 7, and 11 O'clock? Well, I like multiply by .75 a secound time or by .56. If we take
(100 x .75 = 75) (75 x .75 = 56.25)
100 x .56 = 56
2, 4, 8, and 10 O'clock, multiple by .75
1, 5, 7, and 11 O'clock, multiple by .56
I started learning longrange shooting on a .22 LR bolt action rifle then moved to 300 blkout. I was using sub-sonic ammunition for both because I liked how quiet it was and it got rid of the transsonic zone. (In transitioning from supersonic to subsonic the is a barrier causing the bullet to become unstable) Because of this I learned that many aspects of longrange shooting is about time of flight (tof). With our wind formula, because it is calculated by our distance, I had to change the constant (a) to represent a longer tof. I call this "reverse engineering" our wind formula. Being a new longrange shooter at the time and using a .22 lr with subsonic ammo (1070 fps) and shooting out to 300 yards (sometimes 500) I knew I had a huge challenge ahead of me, so I came up with this. For a subsonic .22 lr, I use 2.5 for the constant. If I want to be more accurate, I'll use the following:
100 - 2.3
200 - 2.6
300 - 2.7
400 - 2.7
500 - 2.7
Basically, all I did to find a new set of constants is use the wind formula, and change the constant (a) until both the wind formula and the ballistic calculator had the same answer. Next, I check the formula with 5 and 10 mph winds and with angles to confirm it would work. It works on paper so then I went to the range to test it out. Yep. It worked!
THE OVERWATCH
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