What effect does wind have on a bullet?


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gamestalker
March 24, 2011, 04:00 AM
I really enjoy punching paper at distances out to 500 yds. with my high powered rifles. Is there a method of determining what amount of drift a cross wind will have on the bullet. An example of my average senario is shooting a 120 gr. V-Max bullet from a 7mm rem. mag with a MV of 3400 fps. at 500 yds. Often I'll be dealing with a breeze of 5-10 MPH. So for the sake of this question lets say thier is a steady 10 MPH cross wind, I'm shooting at 3000 feet elevation, the temparature is 90 degrees, humidity 10%. I'm not certain what the B.C. for this bullet is, but lets go with .390, I think that is pretty close for that bullet.
I've been hand loading and shooting like this for almost 3 decades and have heard different answers that vary greatly. So I thought I would ask in this site knowing someone will have a more specific, and scientific accurate answer.
My books indicate the above MV with a given BC takes about a half second to travel 500 yds. I can calculate my trajectory accurately, but I don't understand the drift from a cross wind. I obviously see that the cross wind effects my windage depending on the speed of the cross wind, I would just like some idea of how much the wind will change my point of impact. I think the element of this that has perplexed me is the short flight time of the bullet. And if I shorten the distance to say 200 yds. with the same MV, time of flight is far shorter. So even though once again I see some effect at just 200 yds., it just doesn't seem to be worth worrying about even with a 15-20 mph cross wind, or is it?
If someone can provide the average effect per mph, that would really appreciated. My Son has an electronic device that measurer's the wind speed, so I could easily calculate it's effect with your help.

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Onmilo
March 24, 2011, 08:55 AM
One inch per 100 meters per 10 miles per hour.
This is a very basic wind dope I was taught many. many years ago.
It works fairly well for about all the standard calibers, magnums and wildcats might cut it in half.

paul
March 24, 2011, 09:34 AM
If you've been shooting out to 500 yards for the last 30 years and are just now noticing that the wind affects the flight of the projectile, I don't quite know what to tell you...

But I do wish you luck.;)

p

Jim Watson
March 24, 2011, 09:39 AM
I use JBM to calculate trajectory and windage. It will calculate everything you can imagine using every input you can find.
http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

SlamFire1
March 24, 2011, 09:58 AM
I shot a 1000 yard match sunday, wind blew me out of the ten ring to the 8 and seven ring several times.

Mirage looked the same, flag same, yet out they went.

Wind doping takes time and study. Each range has different wind indications and patterns. Wind is never a constant, cannot be predicted as it is a chaotic phenomena. What it is doing right now has no bearing to what it will be doing a minute from now.

(You will run into people who think they have a system of predicting wind. This is due to the human mind wanting to and “seeing” patterns where there are none)

The Port Malabar Range in Florida hands out you a coin if your first long range shot hits the X ring. Having pulled long range targets and shot the game for years, you are doing good if your first shot hits the black!

txhoghunter
March 24, 2011, 12:31 PM
My Son has an electronic device that measurer's the wind speed, so I could easily calculate it's effect with your help.

Calculating wind at the muzzle is what this device is used for, and it is a great help.

However, to accurately compensate for wind, you must be able to estimate wind further downrange by using flags, trees, mirage, and/or other clues. This takes alot of practice because you not only have to read the speed of the wind, you must know the angle that it will be impacting the projectile and how much of the wind (the "value") will actually be affecting the round.

Jon_Snow
March 24, 2011, 01:55 PM
OP, check out any of the free online ballistic calculators. Hornady has one on their site but I know there are others.

hermannr
March 24, 2011, 02:13 PM
Sierra's 120 grain in 7mm has a BC of .420.

There is a balistic calculator here: http://www.biggameinfo.com/index.aspx?page=%2fbalcalc.ascx

buck460XVR
March 24, 2011, 06:26 PM
If you've been shooting out to 500 yards for the last 30 years and are just now noticing that the wind affects the flight of the projectile, I don't quite know what to tell you...

But I do wish you luck.;)

p

Now THAT'S funny.................:D

BullfrogKen
March 24, 2011, 06:36 PM
All your questions are answered and explained here.


Applied Ballistics for Long Range Shooting (http://www.thehighroad.org/showthread.php?t=564891)


By the way, the V-max really doesn't do well at all at long range. The bullet profile doesn't handle distance well. 500 yards really is about the maximum distance before the poor aerodynamic design catches up with it. I've gotten great groups with mine in .308 out to 500. Beyond that, forget it.

Millwright
March 24, 2011, 07:42 PM
"Curiouser and curiouser" as said Alice. ....

Wind, (cross, head, quartering, tail) effect a bullet's flight from the time it leaves the muzzle until it impacts the target. Head and tail winds have the effect of increasing/decreasing the effective range, hence vertical impact point. "Cross" winds can make you cross, TBS, as their effects can influence bullet impact in range and windage depending upon angle to line of flight. It all comes down to bullet flight time and bullet weight. The longer wind has opportunity to influence bullet trajectory, the more it will effect impact point. One reason so many opt for those laser-quick calibers. Less "time of flight" for wind to effect trajectory......But Newton, (Sir Isaac, not Fig) plays a part, too. Heavier bullets tend to resist wind drift more than those little pills due to differences in inertia.

As a long time varmit shooter I'm only noting observations based upon real world experience. Those laser fast lite pills work OK in still conditions, but drift a lot in wind, making long shots at small targets more problematic. Heavier, (for caliber) pills tend to "buck the wind" better even if they're slower and exposed to its effects longer.

Lots of very good ballistic programs out there. Some will even run on your cell phone. All will work better if you input good actual ballistic data on the particular round/rifle you're using. Getting that data means more trigger time, but hey that's not an issue is it ? >MW

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