Rifle Scopes wind adjustment

[mdmp5]

So I think I have the crosswind adjustments down. However, I am unclear about headwinds and tailwinds. For example, if you are shooting a .308 at say, 600 yards with a straight headwind or tailwind of 10 <span style="text-decoration: line-through">knots</span> mph, how do you adjust for it?

 

[sobrbiker883]

Re: wind adjustment

tailwind you may need a little less elevation, headwind a little more, probably not any more than .1-.2 mil at that range with a 308 though.
Wind is rarely without any side to side component however...

 

[mdmp5]

Re: wind adjustment

So no equation for the y-component? Just add or subtract a small amount of clicks?

 

[Lowlight]

Re: wind adjustment

According to Pejsa, at 500 yards where a crosswind would move the bullet 23.4 inches, the same headwind would move the bullet .21 inches... he had a formula to figure it, and its always tenths of an inch compared to any crosswind effect.

So, basically unless you are shooting 3" groups or smaller at 600 yards, I wouldn't sweat the headwind / tailwind shit, as it's trivial compared to the crosswind component.

the only time I have seen winds, not directly across the flight affect the bullet is in the mountains where updrafts and downdrafts will blow the bullet above or below the target. That is usually based off the winds deflection around things.

 

[TiroFijo]

Re: wind adjustment

The horizontal effect of a tail or head wind is negligible, but the problem is that rarely the wind is truly in line with the shooter.

Even a relatively small angle can move your POI horizontally. One minute on a analog clock face is 6º, and sin 6º = 0.105 = 0.5 MOA at 600 yds with a 308, with a 10 mph wind. If you have a strong wind that fishtails 5-10º to each side then you have a large variation.

 

[Lindy]

Re: wind adjustment

A ballistic program which correctly calculates the effect of a 10 mph headwind on a typical .308 load at 1000 yards would have you add 0.1 mil to your elevation setting, because the headwind causes a slight increase in drag on the bullet compared to still air.

But that's within the range of the variation in point of impact caused by the normal variation in muzzle velocity.

So, the elevation effect for most velocities of headwinds or tailwinds may be safely neglected.

 

[mdmp5]

Re: wind adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">According to Pejsa, at 500 yards where a crosswind would move the bullet 23.4 inches, the same headwind would move the bullet .21 inches... he had a formula to figure it, and its always tenths of an inch compared to any crosswind effect.

So, basically unless you are shooting 3" groups or smaller at 600 yards, I wouldn't sweat the headwind / tailwind shit, as it's trivial compared to the crosswind component.

the only time I have seen winds, not directly across the flight affect the bullet is in the mountains where updrafts and downdrafts will blow the bullet above or below the target. That is usually based off the winds deflection around things. </div></div>

Gotcha. Thanks Frank.

 

[mdmp5]

Re: wind adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">The horizontal effect of a tail or head wind is negligible, but the problem is that rarely the wind is truly in line with the shooter.

Even a relatively small angle can move your POI horizontally. Five minutes on a analog clock face is 6º, and sin 6º = 0.105 = 0.5 MOA at 600 yds with a 308, with a 10 mph wind. If you have a strong wind that fishtails 5-10º to each side then you have a large variation.</div></div>

You mean 1 minute right?

 

[mdmp5]

Re: wind adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">A ballistic program which correctly calculates the effect of a 10 mph headwind on a typical .308 load at 1000 yards would have you add 0.1 mil to your elevation setting, because the headwind causes a slight increase in drag on the bullet compared to still air.

But that's within the range of the variation in point of impact caused by the normal variation in muzzle velocity.

So, the elevation effect for most velocities of headwinds or tailwinds may be safely neglected.
</div></div>

I understand. Thanks for the input Lindy.

 

[sobrbiker883]

Re: wind adjustment

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">the only time I have seen winds, not directly across the flight affect the bullet is in the mountains where updrafts and downdrafts will blow the bullet above or below the target. That is usually based off the winds deflection around things. </div></div>

Those winds would be acting as a crosswind would (same type of vector) only from above or below, I'd venture that windage dope could be applied to the elevation adjustmen in the same fashion as the "clock value", but thinking of the line of sight as 12:00 and 90* up from muzzle as 3:00.....if that makes any sense at all.

 

[Lindy]

Re: wind adjustment

The difficulty is in trying to judge the magnitude of the updraft or downdraft.

The practical solution is watch the impact of the first round, and adjust from there.

 

[sobrbiker883]

Re: wind adjustment

I'm agreeing none of this is an easy task, but the "miss first then make an adjustment" philosophy isn't the best effort.

Of course one should always call their shot and make every effort to see the impact on or off target and be ready to adjust, but I'm always trying to find ways to better my probability of a not missing to begin with. Isn't that part of the whole exercise of taking a shot?