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Wind effect on bullet.

2950 Views 12 Replies 5 Participants Last post by  PrepConsultant
I said before I would post the wind calculation I use for long range shooting. As those of you know, I LOVE to shoot long range. I did not come up with this but it is one of the better and easier to remember ones I have found. The amateur is concerned with trajectory, the professional is concerned with wind effect.. The person that taught me also has several articles in mags and a website I will post if I can find it.. This calculation is for the 175gr .308 but I will also tell you the conversion for the 5.56,300 win mag, 338 LM and 50 BMG.

There are 3 steps.
First is you make your calculation based on a 10mph full value wind effect.
Adjust for actual wind speed
then adjust for actual wind value.
This is very simple once you get used to it and you will be able to do it in your head very quickly.
The formula is range in yards expressed as a single digit. minus 1. So 700yds is 7 minutes of correction-1. 500yds is 5 minutes then minus 1.

Next is actual wind speed. A 20 mile an hour wind will affect the bullet twice as much and a 5 mph wind will affect it half as much.
So if you have a 700 yd target with a 5 mph wind. It will go like this 700 yds (7minutes-1 = 6) Then since it is only a 5mph wind you divide the 6 by 2 and have a 3 minute correction at 700yds.

Next is actual wind value.A lot of places teach only no value,half value and full value which will get you on a man sized target out to about 600yds but to get further or more precise, I prefer this.\
15 deg is 1/4 val
30 deg is half val
45 deg is 3/4 val
65 deg is 9/10 val
90 is a full value

So, if you have a 700 yd target with a 5 mph wind at 45 deg(3/4 value) It will look something like this 700yds (7minutes-1=6) then since it is a 5mph wind we cut the 6 in half to get 3. Then with the actual wind with the 3/4 value we multiply the 3 x .7 = 2.1 so you would round to a 2 MOA hold or dial...The actual calculation would be .707 but you don't have to be that detailed.

Remember, you are starting off with your range-1 with a 10mph full value effect then adjusting from there. This is for the .308 175gr. It works ont he 168 pills out to 600 or so then gets a little wide. It becomes very easy with practice. Also If you are shooting at say 635 I would round it down to 600 so 6-1 then the rest of the calculation..

If you are shooting
5.56 77 grain ammo you would use range=moa not minus 1 so 700yds is 7 then rest of calculation. You do everything the same except don't minus the 1. This also works out to about 600yds or so.
Next is the 300 win mag. so you can add one more step. The 190 grain 300 wm bullet is affected .7 times as much as the .308 so in the step 4 you would just multiply your calculation by .7
The 338 Lapua is affected .6 times so you would multiply whatever you get by .6
And then finally the 50BMG is .4 so you would just multiply by .4.

I hope this helps. Like I said, I didn't come up with this but it works very good and is the one I use most of the time. It is VERY easy to do in your head and can also be done very quickly.. Just make sure you know your wind speeds and ranges and you will be reaching out there and touching someone..
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Let me break this down to layman's terms

If you target is over 400 yards hold over his head and if you have a crossing wind, hold 1 "head width" into the wind at 400 yards and 3 "head withs" at 500 yards and 8 head withs at 600 yards for every 10mps of cross wind.

With this said unless you shoot long range as a habit, don't shoot over 400 yards in any kind of wind.

Read the last line and repeat after me, unless you shoot long range as a habit don't shoot over 400 yards.

I know of few people under field conditions that can reliably shoot over 400 yards, of course I am talking hunting conditions which is the perfect scenario, pressure, altitude, temperature, position, which is all the variables that apply.

We don't have to wait for them to be within 50 yards as in the civil war, but the closer they are the better chance you have of a good shot, I would suggest that untrained personell start shooting at 100 yards.
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