Other than fundamental marksmanship skills, determining the right elevation and windage for accurate shot placement is a challenge; there lies the great success of the HORUS reticle. Elevation is by far the least problematic given today’s laser range finders which are capable of 1 meter accuracy in the popular commercial brands. Military and high-end commercial range finders will get you consistent sub-meter accuracy. However, wind remains a major factor in precision shooting. The problem with wind calls is that unlike range finders there is no instrument that will give you the shooter an aggregate wind vector acting on your projectile in flight. Therefore good wind calls are really best guestimates based on increasing shooter experience. Wind meters like the Kestrels are indispensible tools but they only provide wind data at the shooting position and a lot can happen between the shooter’s position and your 800 meter target. The fact is that people are better at judging distance than they are at calling wind. So, we’re putting out this little horse that you can ride to success.
Wind corrections are all right triangle trigonometry. Take a look at the figure on the left. “A” is the shooter’s position, “C” is your target and “B” is your bullet impact. Line “a” is your eyeball estimate of how much correction you need to have POI and POA coincide. Line “b” is your range to the target measured with an LRF, given to you or measured optically.
What we need to do next is calculate the angle formed by line “c” and “b” the multiply that value by 17.45 to get the millradian correction. I’m not going to make you calculate all this out. You’ll use your smart device for that. I use Android so I recommend that you download and install Triangle Solver.
Here’s what the screen looks like…
Let’s try a scenario. You fire at a 650 meter target and notice that your point of impact was right of the POA by approximately 22 inches. Enter 650 for your “b” value and enter 0.56, which is 22 inches in meters, for your “a” value. The app instantly calculated “A” which is the correction angle of 0.049 degrees; now multiply that value by 17.45, the result is .855 mills. To correct your fire apply .855 mills Left or Right to what is already dialed in or use your horizontal stadia and hold .8 mills.
The entire process takes 30 seconds from start to finish. If you’re working with a spotter it’s probably even quicker.
As we mentioned earlier, this is a little horse you can use to help you out but it does not substitute developing and maintaining wind estimation skills.