Thinking about wind drift...

[Tomekeuro85]

I was just thinking today, and I realized that because of my relative inexperience with shooting (I've fired less than 600 rounds out of 2 rifles in my life) I never really worried too much about wind drift. I just shoot whenever I am ready, regardless of wind conditions.

Could this be a reason for some flyers in my groups that are like 1/2" away from the rest of my group in .308 and like 1" away in .223 at 100 yards?

How much of an effect will wind have when I get to 300 yards?

How much of an effect does wind really have at 100? I noticed that the days without wind my groups were better than the windier ones.

 

[30Cal]

A 10mph crosswind (full value) is worth almost an inch at 100yds with a typical centerfire (223/308/30-06 sort of ballistics). You may see 5-10mph gusts, so that would push a bullet 0.5-1.0"

At 300yds, it would be worth about 6" and at 600yds, it'd be with ~30" (4-6MoA).

 

[Tomekeuro85]

wow thats quite a bit, especially further out. What do you guys do to eliminate this wind effect?

Adjust windage? OR just wait for the wind to die down?

Also, what do you do in cases at around 600 yards where there could be dead calm by you but a windstorm halfway there and dead calm again at 600? Is this just luck or something?

Either way, at least now I know why my groups always had some stupid random far away hole.

 

[30Cal]

In a highpower match, you generally don't worry about 200yds unless it's really gusty--it takes quite a bit of wind to blow you out of the 10-ring (2MoA circle).

At 300+, it's good to keep an eye on the wind before you shoot so that you can know what to expect--is it relatively constant or does it build or does it let off. During the rapidfire stage at 300yds, you keep an eye on the flags w/ your periferal vision, and check carefully after you've completed your magazine change--hold off (tough to do) or crank the windage if you need to. There isn't time to wait it out.

In slowfire, you watch the mirage and flags for indications that the wind has changed. If you shoot quickly, there's less change. Depending on the nature of the wind, I'll sometimes hold for 2-6 minutes and wait out a change. For smaller changes, I'll keep clicking and shoot on through it.

 

[Zak Smith]

Here's a range data-card for a typical 308 load. Most guys I know, shooting out to about 1000 yards, will list the 10mph value on the range-card, and then scale that based on how much wind they judge to be present between the shooting position and the target. Correction can be done with sight adjustment (knobs, or iron sight adjustment like in H-P), or reticle holdoff, depending on the reticle features.

175 SMK: 2650fps 100yd 2000'
RANGE  ELEV-  moa    mil     | WIND(10) moa   mil   RANGE
  25    1"    3.75   1.1mil  |   0"   0.25   0.0mil   25
  50    0"    0.75   0.2mil  |   0"   0.25   0.1mil   50
  75    0"   -0.00  -0.0mil  |   0"   0.50   0.1mil   75
 100   -0"    0.00   0.0mil  |   1"   0.50   0.2mil  100
 125    0"    0.25   0.1mil  |   1"   0.75   0.2mil  125
 150    1"    0.75   0.2mil  |   1"   1.00   0.3mil  150
 175    2"    1.25   0.3mil  |   2"   1.00   0.3mil  175
 200    4"    1.75   0.5mil  |   3"   1.25   0.4mil  200
 225    6"    2.25   0.7mil  |   3"   1.50   0.4mil  225
 250    8"    3.00   0.9mil  |   4"   1.75   0.5mil  250
 275   11"    3.75   1.1mil  |   5"   1.75   0.5mil  275
 300   14"    4.25   1.3mil  |   6"   2.00   0.6mil  300
 325   17"    5.00   1.5mil  |   7"   2.25   0.6mil  325
 350   21"    5.75   1.7mil  |   9"   2.25   0.7mil  350
 375   26"    6.75   1.9mil  |  10"   2.50   0.7mil  375
 400   31"    7.50   2.2mil  |  11"   2.75   0.8mil  400
 425   37"    8.25   2.4mil  |  13"   3.00   0.8mil  425
 450   43"    9.25   2.7mil  |  15"   3.25   0.9mil  450
 475   50"   10.00   2.9mil  |  17"   3.25   1.0mil  475
 500   57"   11.00   3.2mil  |  19"   3.50   1.0mil  500
 525   65"   11.75   3.4mil  |  21"   3.75   1.1mil  525
 550   74"   12.75   3.7mil  |  23"   4.00   1.1mil  550
 575   83"   13.75   4.0mil  |  25"   4.25   1.2mil  575
 600   93"   14.75   4.3mil  |  28"   4.50   1.3mil  600
 625  104"   15.75   4.6mil  |  30"   4.75   1.4mil  625
 650  115"   17.00   4.9mil  |  33"   4.75   1.4mil  650
 675  127"   18.00   5.2mil  |  36"   5.00   1.5mil  675
 700  140"   19.00   5.6mil  |  39"   5.25   1.6mil  700
 725  154"   20.25   5.9mil  |  42"   5.50   1.6mil  725
 750  168"   21.50   6.2mil  |  46"   5.75   1.7mil  750
 775  184"   22.75   6.6mil  |  49"   6.00   1.8mil  775
 800  200"   24.00   7.0mil  |  53"   6.25   1.8mil  800

 

[Bullet]

Here is a link to help you figure wind and elevation –

http://www.eskimo.com/~jbm/calculations/traj_basic/traj_basic.html

http://www.eskimo.com/~jbm/calculations/calculations.html

 

[pat86323]

The bullet weight will have alot to do with that. Also something to keep in mind is that you will likely not be able to hold as steady with a wind, which could screw up your calculations on how much wind effects the bullet travel.

 

[Zak Smith]

Once you have BC, the bullet mass is irrelevant with regard to external trajectory.

 

[nbkky71]

Here's a quick & dirty windage formula that was taught to me years ago by another highpower shooter. This formula assumes full wind (i.e - 90 degree) values.

(Range in hundreds of yards x wind speed in MPH) / math constant

math constants
100 yards: 15
200 yards: 15
300 yards: 15
400 yards: 15
500 yards: 15
600 yards: 14
700 yards: 13
800 yards:13
900 yards:12
1000 yards: 11

example:
range to target = 300 yards
10 mph wind.

(3 x 10) / 15 = 30/15 = 2 MOA

 

[30Cal]

That formula is straight out of FM23-10 (Sniper field manual). I just have a decent feel for what 10mph does at a couple of points (2, 3 and 6). Then I try to bracket the wind value (no less than 3', no greater than 6' so lets use 4.5).