How do you calculate wind drift?

18 May 2003, 08:13

I was reading a book and came across a chart of wind drift for typical .308 match ammo at different range and different wind speed/angle. Then all of a sudden it struck me : "I don't know how to calculate wind drift of a given bullet and given muzzle velocity!" [Eek!]

In the field or long range matches this is going to be important, I appreciate any info.

Pyrotek

18 May 2003, 08:20

N E 450 No2

Pyrotek, Any of the good Reloading books have wind drift info. If you are a serious long range shooter you need a wind "spedometer". Most people over estimate the wind. You can get one from
www.sinclairint.com

18 May 2003, 08:54

Olimahtes

There are numerous ballistic programs that can give you the data you are searching for. The ones I have tested seem to be quite reliable. Here is a Swedish one. Don't worry, it is also available in english. Besides the trajectory estimating function, there are some other functions that are quite nice to play with on those dark winter nights.

www.robsoft.nu

Please inform me if I'm violating the rules by presenting this link. In that case I'll remove it instantly.

18 May 2003, 09:13

Jameister

These guys got it backwards. shoot your bullet. go to target. measure the horizontal error. that is how much drift you have.

IF you want a better way, go to the Norma ballistics website and play with the nomograms there.

http://www.norma.cc./htm_files/javapagee.htm

Everything you need to know for free.

for example, I just loaded 308 165 grain bullet.

at 200 yards with a 29.9 mph crosswind, it will drift 12 inches.

plug in your speed and bullet weight adn distance and angle, and it will show the drift.

18 May 2003, 10:51

Olimahtes

quote:
Originally posted by Jameister:
These guys got it backwards. shoot your bullet. go to target. measure the horizontal error. that is how much drift you have.

IF you want a better way, go to the Norma ballistics website and play with the nomograms there.

http://www.norma.cc./htm_files/javapagee.htm

My experience is that it's hard to get a reliable empirical value since the wind tends to shift a bit in speed and sometimes also in direction between the muzzle and the target. The modelled data gives you a stable foundation to build your future empirical experience upon. I think that a good way to learn to read the wind is to analyze why the true drift didn't match the calculated?

Normas ballistics program is not better than the one from robsoft. I think it's pretty much the other way around.

18 May 2003, 13:18

Jameister

When I opened robsoft, I got a page under construction, and then a nice worksheet,but no place to enter wind speed ro direction.

The Norma page shows you effect of wind drift instantly for each distance and direction you ask, for any wind speed up to 29.9 mph.

to each his own...

18 May 2003, 20:02

Olimahtes

quote:
When I opened robsoft, I got a page under construction, and then a nice worksheet,but no place to enter wind speed ro direction.

Try "software" instead. Then you can download a program that does a lot of interesting things: Trajectory, bullet stability and wind drift calculations, among other interesting things. I recommend trying it. You can try it for free for a month.

The reason that I'm pushing for Robsoft is that it's made by a small swedish company. Normas ballistics program is really ok too. No question about it.

[ 05-18-2003, 11:03: Message edited by: Olimahtes ]

19 May 2003, 02:29

<David King>

Easy rule of thumb for a close guestimate.

With a 308 Win class rifle use 1 MOA for each 10mph of full value wind but begin compensation at 200 yards.

10 mph wind, 90 degrees to flight path, 300 yards...adjust 2 MOA on windage dial, 10 mph 500 yards...4 MOA.

(I generally shoot only 168 and 175 Sierra MKs but this should be sufficiently close for other rounds in this category.)