Is Wind drift linear?

Subsonic bullets are affected vertically by air friction against the rifling marks to a much greater extent than supersonic bullets, which have a shock wave that minimizes air flow along the parallel body of the bullet and the "fins" created from rifling.

Exception: Bullets, like barely supersonic .22LR high speed bullets that, as they slow down between muzzle and target, pass through the supersonic>subsonic transition zone, which causes them to deflect horizontally about 1/3 more than bullets that either stay supersonic, or start as subsonic rounds.
 
Actually it is exponential to wind because as you change the path of the bullet you are changing the distance.

Imagine shooting into a wind so strong you had to aim 45 degrees off line of sight to get your bullet to the target, as you can see, the bullet now has to travel a much longer path and it would in a no wind condition. As the bullet path distance increases, corrections have to get larger and larger for each correction, something you would expect from an exponential (or trigonometric) function.

For small wind values, 20mph or less, obviously a linear approximation is accurate enough. But don't confuse a linear approximation of an exponential for linearity.

Jimro
 
Were in the hell do you guys shoot were the wind blows at the same speed and direction all the way to the target?]
Click to expand...

Guess you have never shot in Wyoming!

A better question would be "Were in the hell do you guys shoot were the wind only blows 5-10 mph?" :D:p
 
Madcratebuilder asked were in the hell do you guys shoot were the wind blows at the same speed and direction all the way to the target. There's four rifle ranges I've shot at where the winds under 5 mph are very consistant in speed and direction and the terrain's very flat:

Camp Perry, Ohio, Viale Range on the 1000 yard line when the wind's from the northeast coming in from Lake Erie.

Puuloa Rifle Range at Ewa Beach west of Honolulu, HI, at what's now a Naval Magazine area when the wind's from the southwest.

Colorado Rifle Club range about 10 miles north of Byers, CO when the wind's from the east.

Sho-Bon Rifle Range east of Shoshoni, WY, that's no longer there. Any wind from the south was very consistant across its 1000 yard range.

There's lots of antelope hunting areas in the flatlands of northeast Colorado as well as south east Wyoming where this happens.
 
Last edited:
I was hunting coyotes last weekend between Shoshoni and Casper. The wind was from the west at a constant 30 mph. I couldn't hit anything with my .204 with those 32 gr Hornadys! Should have brought my .30-06, I might have connected on a few!

Reading wind drift seems more of an art than a science, to me.
 
Best guessing for a wind correction I've seen was at the 1988 World Long Range Palma Matches in Sydney, Australia. Practice day before the matches started had mild winds in spite of the range being 200 yards away from the beach. On the day of the big team match, the wind Gods had turned on their after burners. I measured wind speed from 8 o'clock on the range at the 800 yard line on my gauge at 30 to 35 mph. All four US team line coaches as well as the head coach felt the first sighter should be made with 29 minutes of left wind so we all went 116 clicks left for openers. That pointed the barrel over 24 feet to the left of the target when our sights were on the bullseye. I and one other guy on the first relay shot first and our shots were about 3 seconds apart; mine struck the 4 ring on the left side, his the 4 ring on the right side. Both missed dead center in the 5 ring by about 20 inches. Such is life when the wind gusts as I fired and his bullet caught more of it than mine did.
 
Bart B. --- If I misquoted David Tubb...I want to make my apologies to David Tubb. No doubting, what you said is true ---that is --- hunting for mirages with your spotting scope at 1,000 yards. You can tell...I'm a novice, in long range shooting sports --- for the furthest I've shot --- is 200 yards, at the AGC gun range located on Marriottsville Rd, in Baltimore County, Maryland.

Thanks for the input.

Cheers,

Erno86
 
Madcratebuilder asked were in the hell do you guys shoot were the wind blows at the same speed and direction all the way to the target. There's four rifle ranges I've shot at where the winds under 5 mph are very consistant in speed and direction and the terrain's very flat:

Camp Perry, Ohio, Viale Range on the 1000 yard line when the wind's from the northeast coming in from Lake Erie.

Puuloa Rifle Range at Ewa Beach west of Honolulu, HI, at what's now a Naval Magazine area when the wind's from the southwest.

Colorado Rifle Club range about 10 miles north of Byers, CO when the wind's from the east.

Sho-Bon Rifle Range east of Shoshoni, WY, that's no longer there. Any wind from the south was very consistant across its 1000 yard range.

There's lots of antelope hunting areas in the flatlands of northeast Colorado as well as south east Wyoming where this happens.
Click to expand...

There are exceptions to everything, but most ranges are build facing hill sides or have breams for safety. The majority on my long range shooting done hillside to hillside on blm land. Occasionally I well cross the mountains to the flat scrub lands. You well seldom have the same conditions from the firing line to the target.
 
It gets drafty at 29 Palms.

I shot a service rifle (M1A/308s) 1000 yard match one year in some wind that woud make Wyoming proud.

Took me a bit to get on, but when I did I was shooting lots of right wind and aiming at the neighbor's target. Had a good string going until.....

The range officer told the line, to notify the pits if you finished or quit shooting so they can pull the targets to keep the wind from tearing them uo.

As I said I was doing good, then someone pulled target. I call to have my target put back up and my scorer says, "Your Target is Up".

I had to start all over, lost quite a few points.

It's all fun.
 
kraigwy, I spend little time at 29 Palms and I spend about 2yr working at the Wheatland Power Plant then almost yr at Ft Warren the few project from Laramie to Rock Springs and you guys have wind. We have wind here in Co but nothing like you guys. Don't mean to disagree with you
 
Old Roper, Wheatland, FE Warren, Laramie, I-80 corridor, Rock Springs! Man you have lived in all the best WYoming has to offer...as far as wind goes!:eek:
 
I have been doing some thinking about how to make wind drift more understandable.

When you are driving a car down the highway and you spit out of the window, it looks like the wind outside the car takes whatever you spat out and blows it backwards.
But there is no wind out there, the "wind" you feel when you stick your hand out the window is due to the motion of the car. What you really saw was the velocity of the spit, which started off going forward just as fast as the car was going, slowing down and your car, which was not slowing down, leaving it behind. That spit actually went in a straight line from a stationary reference point.

OK, instead of the air moving, let's assume the shooter and target is what's moving. We have a shooting station on the deck of a ship and a target on another ship 200 yards away and both ships are traveling parallel to each other in the same direction at 10 mph in a dead calm. The ship's speed makes this dead calm look like a 10 mph crosswind.
The bullet obviously travels a straight line because the wind is actually calm.
Because the target is moving, the shooter has to lead the target just like when shooting at flying birds with a shotgun.
But the shooter is also moving and that motion gives the bullet the lead needed to hit the target. Gunners will tell you that when you are strafing ground targets out of the side of a helicopter gunship, you have to lead those ground targets just as if the helicopter was stationary and the ground was moving under you.
So these two things cancel each other out, as long as the bullet does not arrive late. The later the bullet arrives, the more behind the target the bullet hits.

Now consider a .17 HMR with a muzzle velocity of 2550 fps.

At 2550 fps, it takes .235 seconds to travel 200 yards, but the bullet slows down, at 100 yards it's only going 1900 fps and at 200 yards, it's down to 1380 fps and as a result, it takes it .324 seconds to go 200 yards. Subtract .235 from .324 and we see that the bullet arives at the target .089 seconds late. Since 10 mph is 14.667 fps, 14.667fps X .089 seconds is 1.3 ft or 15.6 inches more that the target moved while waiting for the bullet to get there.

Now let's look at a Whisper 300 shooting a 220 grain hpbt with a BC of .608 with a muzzle velocity of 1040 fps.
At 1040 fps, it should take .577 seconds to reach that target.
But at 100 yards, this bullet has slowed to 1002 fps and at 200 yards it has slowed to 970 fps and as a result it took it .598 seconds to go 200 yards.
This bullet is .021 seconds late and .021 seconds is enough time for that moving target to go an extra 3.7 inches.

The more a bullet slows down during its flight, the later it gets to that target and the more it misses the bullseye of that moving target.

Now here comes something that's totally counterintuitive. Let's say the bullet speeds up during its flight. Now the bullet gets to the target early instead of late and instead of underleading this moving target, we are overleading the target and the bullet seems to drift against the wind instead of with it. Of course, bullets never speed up during flight unless you are shooting rocket assisted artillary rounds.
I dunno, maybe rocket propelled projectiles actually do climb the wind instead of drifting with it while the rockets are accelerating the projectile.
 
I dunno...
Maybe I'm oversimplifying it...
Gravity's effect/bullet drop on the bullet is linear as we all know...Newton...

But the reason wind drift is not, is simply because as the bullet loses velocity, the lateral movement increases exponentially per unit of distance traveled simply because it's being "moved" or "pushed" the same distance per unit of flight time, (call it seconds, if you want) but it's covering less and less distance (per second) as it flies downrange so the relationship becomes exponential.

I think.
 
I dunno...
Maybe I'm oversimplifying it...
Gravity's effect/bullet drop on the bullet is linear as we all know...Newton...
Click to expand...

Gravity accelerates stuff that falls. The distance fallen in ft = 1/2 * 32.2 * T^2 where T = seconds.
If the bullet doesn't slow down, you can expect 4X the drop at 200 yards as at 100 yards.

Exponential functions result in a curved path, like a bullet travels.
Linear functions result in a straight path, that's why we call them "linear".
 
The reason wind drift isn't linear is because the speed of the wind is being added to the bullet, sideways. If the wind hit the bullet at 25mph and then completely stopped, the bullet would still be sliding sideways under the momentum imparted by the wind.

Basic physics. An object in motion tends to stay in motion.

The bullet begins to pick up its own horizontal speed.

If the bullet wasn't picking up horizontal speed of its own, drift would be linear.

But the bullet is picking up speed, it's accelerating. That's why the path is curved.
 
Right, the crosswind accelerates a bullet sideways. If the bullet actually kept up with the crosswind, a 10 mph (14.667 fps) crosswind would displace that .17HMR bullet 57 inches instead of 17 inches during the .324 seconds it took that bullet to go 200 yards.

How 'late' a bullet is getting to the target is called the lag time and the moving shooter and target in a calm situation I detailed shows why wind drift is proportional to lag time, not time of flight.
That 220 grain .30 caliber bullet with a muzzle velocity of only 1040 fps took nearly twice a long to reach the target, yet it drifted a whole lot less than that .17 caliber bullet.

BTW, the drifts that my "moving target and shooter" model estimated agree with the wind drifts that ballistics calculators spit out in case no body got that.
 
Exponential functions result in a curved path, like a bullet travels.
Linear functions result in a straight path, that's why we call them "linear".
Click to expand...

Thanks for correcting me. I knew what I meant to say, but stated it incorrectly. What I meant to say was that bullet drop stays the same, regardless of wind velocity.

But isn't it correct that the "curved" horizontal trajectory (drift) of a bullet is due to the fact that it decelerates as it travels downrange?

IF a bullet traveled at a constant rate of speed, the flight path would be a straight line- albeit at a sharp angle to the target to hit point of aim if there were a stiff full-value wind, no?
 
If the bullet could travel far enough, it would eventually be "sliding" sideways at the same speed as the wind. From that point on, the drift would be linear, more or less, depending on which variables you ignore for simplicities sake.

It wouldn't quite be linear because it would be slowing in the forward direction with a constant sideways slide but it would be a lot closer to linear than it was during the time that the wind was accelerating it.
 
B.L.E. said

Actually, wind drift is exponential with distance in a constant wind.

Here's the calculation of a standard velocity .22 long rifle bullet in a 10 mph cross wind.

25 yards 0.3 inches
50 yards 1.3 inches
100 yards 5.1 inches
200 yards 19 inches

It's linear to wind strength, exponential to distance.
Click to expand...


I agree - that's what my programs indicate.
 
A bullet traveling through the air never feels a side wind hitting it. If you are traveling at 1000 mph, what you experience is 1000 mph wind hitting you from the front. The natural wind of the air you are moving through adds, subtracts, or shifts the angle that this wind hits you by a fraction of a degree.
This "apparent wind" slows you down in the direction that the apparent wind hits you so if its direction shifts by a fraction of a degree, you slow down in that direction instead of the direction of your ground path.

Think about it this way and it becomes obvious why it's how much you slow down and not the time of flight that determines your course deviation.

As a bullet slows down, that wind angle also gets bigger, going from a small fraction of a degree to maybe a degree or so. The fact that slow bullets experience a larger headwind angle shift than fast bullets do explains why slow bullets drift more when the decelerations are equal.
 
You must log in or register to reply here.
Back
Top