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-   -   Change in wind affecting the vertical drop in the bullet (http://www.calguns.net/calgunforum/showthread.php?t=495752)

wildog8812 11-02-2011 6:54 PM

Change in wind affecting the vertical drop in the bullet
 
I was wondering, if I had my rifle zeroed with a 10 mph wind left to right at a certain distance and I shot at the same location on a different day with all of the same conditions (ie: temperature, humidity, barometric pressure, ect) except on this day there is no wind, would this effect the drop of the bullet? If so how much? My thought is that if when I shot with my rifle zeroed it may have been a little bit farther because the wind made the bullet have a horizontal arc when being shot as well as a vertical arc and when wind is not a factor it would only have a vertical arc and no horizontal arc. For this example lets say I was taking a 600 yard shot at 10mph my windage adjustment would be 5.3 MOA for a 33" drift. When I tried to calculate for this same shot with no wind my calculations showed that the bullet would travel a fraction of an inch shorter than if there was wind which should not really effect the bullet drop, but I only have so much of a math background and do not know if I did my math correctly. Any information is greatly appreciated.

CSACANNONEER 11-02-2011 6:58 PM

For a true 90^ cross wind, there should be no affect on drop. But, as the wind dirrection changes you will see a drop or rise in your POI.

G-forceJunkie 11-02-2011 7:50 PM

Mathmaticaly, a bullet pushed by a cross wind is traveling a longer distance, but the amount is so tiny you can ignore it with a perfect 90 deg crosswind. But a perfect 90 degree crosswind does not exist.

bubbapug1 11-03-2011 1:00 AM

get a ballistic calculator for your computer and run the scenarios....

RuggedJay 11-04-2011 7:29 PM

If it was tailwind or headwind, depending on how far you are shooting it might make a difference, or so I've been told.

CSACANNONEER 11-05-2011 8:40 AM

Quote:

Originally Posted by RuggedJay (Post 7443133)
If it was tailwind or headwind, depending on how far you are shooting it might make a difference, or so I've been told.

And since most winds are not exactly 90^ cross winds, it's a constant issue. I know that during a match, I've shot in a 2-3 mph cross wind and when the wind stopped, I ended up catching some kind of thermal and the bullet dropped 18" or so at 1000 yards. It wasn't just me experiencing this. Every shooter who fired at the same time experienced the same drop.

Tacticalintervention 11-05-2011 9:49 AM

No comp will give ou the answer. Welcome to the shooting world outside of what models say.

Here is what you need to know. The wind flows over land just like water over land. It is not a flat right to left thing. If the wind hits a berm and goes over it it creates an up draft. If it flows down the other side of the berm it will cause a down draft. In short it all dpeends on when your bullet crosses the wind. Some of it is luck and some is just waiting until the weird stuff stops and shoot in the average.

If you shoot some high level events, on NRA range you will see as conditions start to change the better shooters will normally hold up until the wind settles. Guys just banging away miss this and get more up and don shots than the guys who watch and wait.

PUFF 11-13-2011 10:59 AM

You also have to consider a boil in the mirage. Very few experienced F Class or High Power shooters will shoot during a boil in the mirage. It will cause a distortion in what you see like when you stick a pole in water. The center of the target will appear higher or lower depending on the boil in the mirage. Benchrest shooters also consider the amount of verticle change due to rotational spin drift, but that gets a little too deep in explanation.

buggsb 11-20-2011 8:50 AM

Quote:

Originally Posted by CSACANNONEER (Post 7431592)
For a true 90^ cross wind, there should be no affect on drop. But, as the wind dirrection changes you will see a drop or rise in your POI.

Really??? I'd love to see the math behind some of the comments here.

First, the effect of gravity on bullet drop is completely unrelated to the distance traveled.

Second, any "updraft" substantial enough to counter the gravitational drop would need to be huge.

The best instructors will tell you that if it can't be proved mathematically it's just opinion. There are plenty of myths and urban legends in this discipline which are assumed be fact just because they are repeated often enough.

Tacticalintervention 11-20-2011 1:49 PM

Quote:

Originally Posted by buggsb (Post 7531205)
Really??? I'd love to see the math behind some of the comments here.

First, the effect of gravity on bullet drop is completely unrelated to the distance traveled.

Second, any "updraft" substantial enough to counter the gravitational drop would need to be huge.

The best instructors will tell you that if it can't be proved mathematically it's just opinion. There are plenty of myths and urban legends in this discipline which are assumed be fact just because they are repeated often enough.

Brother based on lots and lots of bullets down range under all kinds of conditions and levels of events

G-forceJunkie 11-20-2011 7:17 PM

It has nothing to do with gravity, that is a constant. We are dealing with distance the bullet travels. A straight line is the shortest distance between two places. When correcting for wind, your bullet is no longer traveling in a straight line (left to right wise) since you have to aim into the wind since it it going to blow it over. Thus your bullet trajectory (again, left to right) is not straight, it is curved. A curved line is longer than a straight one, thus the bullet had to travel a longer distance, thus its flight time was longer. This results in a lower impact, by a tiny amount. But again, its splitting hairs, the flight time is milisconds different, generally small enough to ignore.
Quote:

Originally Posted by buggsb (Post 7531205)
First, the effect of gravity on bullet drop is completely unrelated to the distance traveled.


brian01tj 11-24-2011 10:34 AM

Quote:

Originally Posted by buggsb (Post 7531205)
Really??? I'd love to see the math behind some of the comments here.

First, the effect of gravity on bullet drop is completely unrelated to the distance traveled.

Second, any "updraft" substantial enough to counter the gravitational drop would need to be huge.

The best instructors will tell you that if it can't be proved mathematically it's just opinion. There are plenty of myths and urban legends in this discipline which are assumed be fact just because they are repeated often enough.

Tailwind and Headwind will cause a POI chage because it has an effect on the velocity of the bullet. Since the bullet is seeing an increase or decrease in drag from the wind that means that the bullet is getting there faster/slower.

Here is a section from exterior ballistics:
" In Section 2.0 we discussed the two physical forces, gravity and air drag, which act on a bullet traveling through the air. The trajectory of a bullet is completely determined by these forces after it leaves the gun barrel. The gravitational force does not depend at all on wind conditions, but the air drag force does, and it has a very important influence on trajectory. Drag on a bullet is determined by the velocity of the bullet RELATIVE TO THE AIR THROUGH WHICH IT TRAVELS. When the air moves, the drag on the bullet is different from what it is when the air is still. It is just this drag force difference that causes the bullet trajectory in a wind to be different from what it is in still air.

This is quite easy to see when the bullet flies in a headwind or tailwind only (no crosswind). Suppose that you fire a bullet with a muzzle of 3000 fps and a tailwind of 10 mph. When the bullet leaves the muzzle its velocity is 3000 fps relative to the ground, since you are holding the rifle still relative to the ground. The wind at your back blows toward your target with a velocity of 14.67 fps (10 mph). Then, at the instant the bullet leaves the muzzle, its velocity RELATIVE TO THE MOVING AIR is 2985.33 fps. If there were no wind blowing, the bullet's velocity relative to the still air would be 3000 fps. Since the relative velocity is lower, the drag is a little lower when the bullet leaves the muzzle. As the bullet rides the tailwind, the drag is lower than it would be if the bullet flew in still air all along the trajectory. With less drag, the bullet reaches the target earlier (time of flight decreases), it has more remaining velocity when it gets there, and it suffers less drop (impacts a little high).

If you were firing into a 10 mph headwind instead, just the opposite situation would happen. The bullet velocity relative to the air would be 3014.67 fps at the muzzle. Since the relative velocity is higher than it would be in still air, drag is higher when the bullet leaves the muzzle. As the bullet bucks the headwind, the drag is higher than it would be in still air all along the trajectory. Consequently, the bullet reaches the target later (time of flight increases), it has a smaller remaining velocity when it gets there, and it drops more (impacts a little low). "

Ahhnother8 11-25-2011 2:37 PM

Quote:

Originally Posted by wildog8812 (Post 7431576)
I was wondering, if I had my rifle zeroed with a 10 mph wind left to right at a certain distance and I shot at the same location on a different day with all of the same conditions (ie: temperature, humidity, barometric pressure, ect) except on this day there is no wind, would this effect the drop of the bullet?

Yes, it can. With a right hand twist barrel, the bullet will tend to hit low with a left wind and high with a right wind. Not sure why, but I have seen it on target enough to know to correct for it when the wind changes sides.


Quote:

Originally Posted by buggsb (Post 7531205)
Really??? I'd love to see the math behind some of the comments here.

Yes, really.


Quote:

Originally Posted by buggsb (Post 7531205)
First, the effect of gravity on bullet drop is completely unrelated to the distance traveled.

Except that distance traveled affects time-of-flight, which gives gravity more time to do its thing.


Quote:

Originally Posted by buggsb (Post 7531205)
Second, any "updraft" substantial enough to counter the gravitational drop would need to be huge.

Don't know how "huge" it would have to be, but we see it all of the time on the target.


Quote:

Originally Posted by buggsb (Post 7531205)
The best instructors will tell you that if it can't be proved mathematically it's just opinion. There are plenty of myths and urban legends in this discipline which are assumed be fact just because they are repeated often enough.

Just opinion? That would imply that "science" is omniscient. And there are plenty of facts in this discipline that likely cannot be explained, but after tens of thousands of rounds on target, they also cannot be denied.

Twinspool 11-30-2011 6:56 PM

Loft, drop and slice of golf balls all occur due to rotation and relative velocity differences between surfaces and the fluid they're squishing through. Bullets are in a different Renoylds range, but I can see it happening quite easily.


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