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  Wind drift charts
« on: July 30, 2008, 09:23:16 AM » by bergerbullets
this article is predominantly for those who are interested in precision shooting and are meticulous about their shooting.  i have received some emails in the last month with some questions about the long range shots i take and i decided to write something that will help out.
maybe many know of the importance of drop charts/comeup sheet but very few have realised the importance of windcharts.  the reason is simple, you don't notice much wind drift unless you start moving that target 50meters plus.  take it to 100,110,130,150,170 and you will see that you start measuring your wind drift in feet:) as a matter of fact you don't measure it in Feet but in MILS or MOA. 

what do you need it for.  ok here i will explain something i have devised, tried and tested from 50-160meters and has worked to the point that it gets my shots out there on target with the first or second shot. i have all this on video just in case someone wants to debate it but im open for suggestions:)

first you will need to approach this through your elevation settings. you need atleast 6 zero's at different distances and your muzzle velocity.  everything has to be exact ok otherwise don't do all this.  there are enough parameters that can be wrong so don't induce your own error.  When i say 6 zeros i mean one at close range one at 35meters and the others ideally have to be at 60,70, 80,100.

ok the more information the better.  now you have to run a data chart on chairgun for your pellet and chronoed velocity. use a quality chrono and take the average of the usable shots you have.  if this is wrong the process is fouled.  now that you run a ballistic chart on chairgun compare the drop to your real world scenario, those which you brought with you from the range.  ok they should match, look at the ones of the farthest distance, not the 60meter one but you should be looking at your 80,90,100meter zero.  if they dont match you have to check the environmental conditions on chairgun and input the ones present where you shoot.  then make sure the distance of the sight above the bore is correct.  you might need to play about with the ballistic coefficient to get them to match.  now you can go to Windage and print a list of the wind at various speeds.

what i did is to print one of a 10m/s wind and convert it to mile/hour wind by working out each one. the reason is that chairgun uses metric with metric so you cannot have distance in meters and wind in miles/hour like some programs.  since im use to read wind in mile/hour i had to convert the range to meters and use the appropiate mile/hour reading.  ideally then you print one card for a 1mile/hour wind, then for a 3,5,7 mile/hour wind.  i will show you how to organise them in a way which can be used easily in the field.  this system is also used for fullbore so don't worry its not my invention:)

here is a picture of the ones for full bore and here is the one i devised



now you have a window where you have all the information you need for the range you want to shoot.  remember one important thing.  at longer ranges, your groups will not likely be a ONE hole so when you dial in your windage remember that you will not see the bullet impact exactly where your cross hair is.  What i mean is this, if at 100meters your average group is 3" , if your wind call is correct, the impact will be around an imaginary 3" around the reticle.  the wind call is your estimation of wind on that day.  once you dial in your elevation, its your windcall that will judge your hit or miss.

ok so how do you use that information now.  you go to the range, at first setup a large piece of paper such as A3 paper.  then estimate the wind at your position, thats the easiest way to start with.  if you have a wind meter take it out and place it into the wind to help you gauge the wind velocity and to start getting use to the wind.  please forget about using terms such as force 3 or force 4 etc.. in shooting and ballistic tables all over the world the wind is usually spoken of as a x mile/hour wind or x m/s wind.   if you are in england and USA it will be Miles/hour, if you are in germany or sweden it will be meters/second.

now you need to be able to tell 3 things to get this right
1)the velocity of the wind
2)the direction (use clock system, i will explain why)
3)wind force value.

so lets assume you are shooting at 80m and you know that your average group at 80 is 2".  you think you have a wind of
3 mile/hour for the first 50meters coming in from 2oclock.  you will describe this wind as " 3mile/hour from 2 oclock 1/2 value".
. look up the value of the wind for 1mile/hour  i.e=0.2mils, multiply that by the velocity of the wind 0.2x3=0.6mils.  now that is the correction for a full value wind meaning a wind 90degree to your bullets path or else from 3 or 9 o'clock to your position.  that is the wind that will drift the projectile the most.  now we said that your wind is a 1/2 value so that result of 0.6 has to be divided by 2.  0.6/2= 0.3Right windage. you always correct into the wind.  take your shoot and record the impact and adjustments made.  your first tries will not be so fruitful but after a while you start becoming sharp at it. 
i had a go with Charlie and with Carlos last time out to 130 meters on cigarette packets and metal plate and carlos managed to nail it on a good wind call.  It's a much more challenging form of shooting and remember, your hits will always be as close as the smallest group you and your rifle can manage. 
if you want to have a go at it please come and speak to me when at the range and we will have a couple of shots together so you can learn how to do it too. i was delighted to see carlos doing it.
here are some results at long range, quite close for a first shot:)









the more zeroes you get, the better it becomes because your validation of ballistic chart becomes really spot on.  you will be able to range a target at example 170meters, look at the ballistic chart you have printed, Dial in your elevation and windage and you should be on target even way out there Smiley)  remember this can be done well only by dialing in for holdover is not precise enough and you will be wasting time. another thing is that most reticles do not have more than 4 Mils for holdover so how can you hold over 9.3mils? Smiley there is nothing better or more gratifying than a goodwind call and a solid hit way out there and that little puff rising from the sand or paint that has been nicked off plus that 'ding' Grin
goodluck


« Last Edit: July 30, 2008, 09:54:27 AM by bergerbullets »
Logged

range it, dial it, squeeze the round off.
Certified Precision Rifle Handloader, Basic & Advanced- Russell Simmonds Reloading School - UK

 (Read 1032 times) [1]
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