Bullet Drift From Wind

Yeah ... I've seen worse. Wind drift is one reason snipers have spotters and all sorts things to try and compensate for it.

Yep that's typical, especially with gusting cross wind.

That matches what JBM says the windage should be for that load per JBM. You probably sighted in about 1" of wind.

Yep, that's about right. If you want to shoot in windy conditions you need long heavy for caliber bullets. Now people will want to make it complicated with secant ogives and lots of math (which I can do by the way), but to keep it simple, in general heavy for caliber bullets will go through the wind better. For a .223 that starts around 69 grains, and 75-77 is better.

Yep, right in line with my experience!

The wind is an animal that only practice on windy days will help you to take it down.
A wind meter & ballistics app together will get you close but because of longer distance & manipulation of wind direction by the terrain in between you & target .only practice will help you conquer the wind

The wind is definitely a factor and longer ranges amplify the effects. I have seen the range flags at 200-300-500 yards all blowing in a different direction at the same time. Good luck doping that....

Yes, that is normal. Try shooting at 500 yards with a 14.5" barrel AR and a strong cross wind. In order to hit a man-sized target, you'll need to aim 1-2 body lengths to the side. Shooting with wind makes things more challenging and fun. Wind is not an excuse for missing a target.

Did you mean four feet (4') right or four inches (4") to the right at 200?

Good rule of thumb if you don't have a ballistic app at hand is 1moa per 100yd per 10mph of crosswind.

I hope this isn't too OT, but I have a question for the theoreticians and the guys who shoot in the wind; does a heavy for caliber bullet help with wind drift and if so why?

Theoretically, I understand why a heavy for caliber bullet slows down less than a light for caliber bullet; the drag force only depends on the frontal (cross sectional) area of the bullet (which doesn't change if the caliber stays the same). As the bullet gets longer its mass increases, so the same drag force is operating on a larger mass and thus slows it down (negative acceleration) at a smaller rate.

When I think about wind hitting the side of the bullet, if a heavy for caliber bullet is 1.75 times the mass of a light for caliber bullet, it's about 1.75 times as long, and thus the wind has 1.75 times the area to apply force -- it seems like the light and heavy bullets would have the same wind drift if they had the same time of flight. To me, intuitively, it seems that the lighter bullet would have less wind drift in cases of all but the longest range shots (because the lighter bullet generally reaches its target faster).

Also, if you are a very serious shooter, is the g1 drag coefficient a useful tool for calculating wind drift, or do you use some other coefficient? When I look at the bullet that the g1 coefficient was based on and compare it to a heavy for caliber 223 bullet it's like comparing a cannon ball to a canoe. I understand why g1 would be useful for calculating drop (because you adjust g1 until it fits the drop you observe), but it seems that g1 would underpredict wind drift in any bullet you would shoot from a shoulder mounted weapon.

Thanks everyone, I learn a lot on this board and appreciate your input. There aren't many long range shots (or much wind) where I hunt, so I've never had to learn how to shoot in the wind.

Corn-Picker,

Interesting question. The ballistic calcs consistently say that heavy-for-caliber loads have not only better energy retention due to BC, but better wind performance at least in the calibers I shoot. But now that you bring it up, I don't really understand why.

Wind facts.....

A given crosswind speed close to the rifle has more effect on downrange bullet drift than that same crosswind near the target.

Wind above the line of sight is faster than in the line of sight; how much depends on the terrain. Smooth, open, flat land has lower cross winds at the bullet's maximum ordinate than terrain with low bushes and short trees.

A given crosswind speed close to the rifle has more effect on downrange bullet drift than that same crosswind near the target.

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This is not an accurate statement. Wind at the target has more effect on a bullet than wind closer to the rifle's muzzle. As the bullet flies, it loses speed and is more susceptible to bullet drift closer to the target where it has less speed to cut through the wind.

Put it this way, my 308 at 600 yards with 41.7 gr 4064 and 175 smk needed 32 in of correction to combat the wind. The wind would some times slow down to 3 mph and I had to recorrect to 10 in from original zero. At 900 yards I had less then 4 in of vertical spread. I think with 41.9 gr, I had less then 2.5 in. My horizontal on the other hand varied 6 inches because of slight changes in wind direction.

223 is going to be even worse with those low bc numbers.

browningguy said:

Yep, that's about right. If you want to shoot in windy conditions you need long heavy for caliber bullets. Now people will want to make it complicated with secant ogives and lots of math (which I can do by the way), but to keep it simple, in general heavy for caliber bullets will go through the wind better. For a .223 that starts around 69 grains, and 75-77 is better.

Click to expand...

I was going to mention this as well. That weight is part of the ballistic coefficient determination so more weight leaves you with a higher bc. Bc is really a combination of factors you would normally have to enter one by one but the manufacturer is usually nice enough to just give you a number to plug in with everything figured out.

giggitygiggity said:

This is not an accurate statement. Wind at the target has more effect on a bullet than wind closer to the rifle's muzzle. As the bullet flies, it loses speed and is more susceptible to bullet drift closer to the target where it has less speed to cut through the wind.

Click to expand...

But, the bullet doesn't stop drifting when the wind stops. If you have zero cross wind from 0-150 yards and a 10 mph cross wind from 150-300 yards, the bullet is only drifting for 150 yards. If there's a 10 mph cross wind from 0-150 yards the bullet drifts, and even if there's no wind from 150-300 yards the bullet will continue to drift because it's already moving in that direction.

If you setup the problem with a 10 mph right to left wind from 0-150 yards and a 10 mph left to right wind from 150-300 yards then the answer is less clear, i can run som back of the envelope calculations when I have some time. Intuitively I'd side with Bart, but it's not obvious like it is in the former case.

I think what some folks are forgetting, is that when the wind stops pushing a bullet sideways, the bullet still keeps going sideways to the line of sight at that rate all the way to the target.

If you use good ballistic software to see how many inches sideways per 10 yards of downrange travel the bullet is moving when the wind stops, you can easily calculate how much to the side it will strike in the wind direction when it finally gets to the target.

Here's Sierra Bullets' software plotting wind drift through 1000 yards. Green line's the bullet's horizontal path with a 9 o'clock 10 mph cross wind for the first 333 yards; red line for the last 333 yards.



This assumes the wind speed is constant at all points in the bullet's trajectory. No ballistic software I know of adjusts for wind speed above the line of sight that varies with terrain.