Effects of wind?

[Coues100]

I was wondering how wind, straight on or from straight behind effects trajectory?? How do you calculate for long range shooting? Thanks, Mark

[Charles A]

From the from the front the impact will be higher, from behind the impact will be lower. Depending on caliber, bc, velocity, wind speed and especially range it could be a 1/2minute difference. The problem isnt when the wind is truely from 12 or 6 o'clock, but when its at 1,5,7, or 11 o'clock.

[700]

LR7WSM

This is called "Vertical Wind Component" becàuse the wind causes your bullet to plot higher or lower, rather than just left or right.

Give me an email at brXXXian_sinXXXnott@hotXXXmail.com

remove the XXXs.

I can then get details of your shooting system and make up some charts showing the Vertical Wind Component at different ranges.

Rgds

700

[Richard338]

A head wind will LOWER the point of impact. A tail wind will RAISE the point of impact.
Just picture the limiting case of a tail wind equal to muzzle velocity, then you'd have a vacuum trajectory.
The effect is much less than a cross wind, but I recently shot in a switching head/tail wind that was good for 2MOA up/down.

[jb1000br]

Well, when this question comes up, you will always get both answers...shown here.

I have seen more evidence of a HEADWIND RAISING POI AT LONG RANGE.

But it makes more sense that it would do the reverse at short range...

WHY?

On its way to 1000yds the bullet spend more time CLIMBING then FALLING, so why wouldnt a headwind give the bullet LOFT?

At close range, the trajectory is probably flat enough that it is as simple as the wind adding and subtracting from velocity, meaning a HEADWIND WOULD LOWER POI

Now how bout 2000yds+ The bullet is much slower further out and angling toward earth, so here, the loft may even out the added drop, or the headwind may end up causing a total effect lowering POI -- i cant say much here because i have not fired in enough varied conditions past 1mile to see a pattern.

Personally i think the answer depends on the distance you are shooting, and the flatness of trajectory...and surely other things as well.

The above is based only on a flat fire situation shooting over FLAT ground.

YMMV,
JB

[Richard338]

JB, why do you say it spends more time climbing?
I ran a trajectory calc on JBM's page using 3000fps and a BC of .7.
The apogee of a 1000 yard zeroed trajectory is at 540 yards, but that occurs at less than half the time for the 1000 yards trajectory because the bullet is going faster at first.
I added 20 mph head/tail winds and got predicted lower POI for headwind and raised POI for tailwind.
I had a clear example of a switching head/tail wind at 1000 yards a couple of weeks ago and definately found this to be the case.
Target rifle shooters have a memory trick "heads-up, and tails down" (as in aim up in a head wind, and aim lower for a tail wind).
The effect is small in any case but can get you.

[jb1000br]

[ QUOTE ]
JB, why do you say it spends more time climbing?
I ran a trajectory calc on JBM's page using 3000fps and a BC of .7.
The apogee of a 1000 yard zeroed trajectory is at 540 yards, but that occurs at less than half the time for the 1000 yards trajectory because the bullet is going faster at first.
I added 20 mph head/tail winds and got predicted lower POI for headwind and raised POI for tailwind.
I had a clear example of a switching head/tail wind at 1000 yards a couple of weeks ago and definately found this to be the case.
Target rifle shooters have a memory trick "heads-up, and tails down" (as in aim up in a head wind, and aim lower for a tail wind).
The effect is small in any case but can get you.

[/ QUOTE ]

Richard -- first, forget computer models for this discussion.

I guess i should have been more specific, but left out something

seems TO ME the less flat the traj, the more likely to rise at 1K with a headwind.

It has been observed by those i trust with a 308 and 260, and myself with a 6br.

my 6.5-284 has not been noticably affected my any head/tailwinds encountered at 1K thus far.

IMO 3000fps with a .7BC is FLAT-A$$ traj and many rounds we use cant touch that.

in my mind, i see a flatter shooting round more likely to drop in a headwind, and a round with more drop getting loft.

Like i said -- it depends on too many things to make a rule like "heads up whatever down..."

Also, by "more time" i actually meant distance, and you just showed that was true, even with the flat shooter. 540 compared to 460 -- thats an 80yd diff

IMHO, and YMMV,
JB [img]/ubbthreads/images/graemlins/smile.gif[/img]