I'm currently watching "The SHooter" the premise of the movie is they recruit a retired Marine Sniper to help stop an assasination attempt on the the movies president from "over a mile away" or some such. The Shooter Mark Wahlberg explains that a shot at that distance takes in to affect (effect, I can never get this right) distance, heat, wind, spindrift, corialis effect etc. and "even a slight breeze could mean a miss". Could two big fans arrange perpindicular to the target spaced 10 yards apart screw up such a shot?

It's hard to explain what I mean but I think you guys will understand.

no

quote:

Originally posted by hrcjon:
no

Oh come one, play the game. Why not. I really wish I could illustrate what I'm trying to decribe. SO, say two V8 airboat props wouldn't deflect the round?

A bit of wind might make a few millimeter change in path. At 10 yards that's nothing - magnified over 1,000 yards and it becomes feet.

Based on every ballistics calculator I’ve ever seen, that “slight breeze” is assumed to be acting on the bullet for its entire flight to the target. That’s not always true, of course, and competitive shooters frequently complain that the range flags arrayed to the target are blowing in two different directions. That’s one of the reasons reading the wind is such an art, and the ultimate tool for calculating its effects is where the bullet hits the target.

To answer your question, perhaps one of the good rifle shooters will correct me, but I would be very surprised if the very narrow airstream produced by any sort of fan(s) would have any great effect on a bullet, and especially if they were placed close to the target. If they were close to the shooter, any air nudge to the bullet’s trajectory would be magnified with increasing distance, but it would be pretty small if the wind push was at the end of its flight.

The same principle is involved with shooting through a barrier like glass. The probability of hitting the target is greater the closer it is to the barrier. If, for example, the bullet was deflected at a 10 degree angle, it would miss the point of aim by about 4 inches if the target was 2 feet from the barrier, but it would miss by about 21 inches if the target was 10 feet back; if the deflection was horizontal the first would probably still hit a person, but the second would not.

Added: I just did a quick calculation.
Using my agency’s 308 Winchester duty round and a 60 mph crosswind, at 500 yards the bullet would be deflected a total of about 0.5 (1/2) of a degree. That’s a lot at 500 yards (145 inches), but because wind drift varies with the approximate square of the distance, it would have only 1/2500 of the effect over a distance of 10 yards, or about 0.06 inch.

quote:

Originally posted by sigfreund:
Based on every ballistics calculator I’ve ever seen, that “slight breeze” is assumed to be acting on the bullet for its entire flight to the target. That’s not always true, of course, and competitive shooters frequently complain that the range flags arrayed to the target are blowing in two different directions. That’s one of the reasons reading the wind is such an art, and the ultimate tool for calculating its effects is where the bullet hits the target.

To answer your question, perhaps one of the good rifle shooters will correct me, but I would be very surprised if the very narrow airstream produced by any sort of fan(s) would have any great effect on a bullet, and especially if they were placed close to the target. If they were close to the shooter, any air nudge to the bullet’s trajectory would be magnified with increasing distance, but it would be pretty small if the wind push was at the end of its flight.

The same principle is involved with shooting through a barrier like glass. The probability of hitting the target is greater the closer it is to the barrier. If, for example, the bullet was deflected at a 10 degree angle, it would miss the point of aim by about 4 inches if the target was 2 feet from the barrier, but it would miss by about 21 inches if the target was 10 feet back; if the deflection was horizontal the first would probably still hit a person, but the second would not.

Thank you. That makes a lot of sense. I fully realize this is indeed an off the wall question. I sometimes rhink up weird shit likes this...and I don't even drink.

How fast can you get the fans going? You can make some real strong wind with a Merlin engine on a stand and reversed pitch prop. Might have an effect...

quote:

Originally posted by phxtoad:
How fast can you get the fans going? You can make some real strong wind with a Merlin engine on a stand and reversed pitch prop. Might have an effect...

Now you're thinking.

The are numerous factors in determining the overall effect of wind on the flight of a bullet. Speed, direction and value all play a part. Speed is the easiest to figure out. Direction comes next. Value is the sleeper. If there is a 10 mph wind 90 degries to the firing line at the firing line, the bullet will start it's drift as soon as it leaves the muzzle. If the same wind is 600 yards down range, and the bullet only passes through it in the last 100 yards to the target, the 'value' of that wind is a lot less.

Not a sniper, nor a particularly accurate rifle shooter. But I do have a passing acquaintance with Mr. Newton's laws, and it would hard to imagine a practical fan setup having any major change to a bullet's path.

Omitting math, here's the problem.

To accelerate the bullet off target, you need to apply a force. That would be the side drag applied by the fans, which would of course only apply for the duration the bullet spends in the fan's airflow.

Bullets won't spend a lot of time in the fan's airflow to get side drag blown off-target. They would get a small bit of side displacement while affected by the fan, and then continue on a ballistic path.

This may seem counter-intuitive, so here's a thought experiment - imagine an environment with zero gravity but with atmosphere so the fan could have something to blow - like a space station.

Put the bullet motionless, hanging in space in front of the fan, with the fan aimed sideways to the orientation of the bullet. Turn the fan on for a few milliseconds ( about as long as you'd expect the fired shot to spend in the fan's airstream on the ground), and measure how far sideways it moved in those few milliseconds.

That's the sideways displacement your fan achieved on the target on the ground.

Most likely, not much.

Yeah, that's not the way it works.

When a bullet travels in the atmosphere, the biggest wind it encounters is the wind generated by its forward travel. Because the bullet is spinning it will travel point on, into the wind.

When there is another wind involved, that wind will be added as another vector in the travel of the bullet and the bullet will turn its point a little bit in the direction of that added wind vector. Remembering that a bullet travels at thousands of feet per second, the addition of a side wind vector for 20MPH or even 200MPH is going to pale in comparison to the main wind the bullet is encountering.

So the wind doesn't "push" the bullet per se, it just influences the direction of travel and the drag takes care of the rest to move the bullet from its initial trajectory.

A nice way of testing this is as follows. Get into your car and start driving on the highway. Stick your hand out the window at 60MPH and tell me if you can feel the 5MPH wind coming from the side. Now do that at 2000PH and see if you feel the 5MPH wind.

For the purposes of this thread here, there would be no effect on the bullet with whatever fan(s) you can put in front of the speaker.

quote:

Originally posted by SgtGold:
The are numerous factors in determining the overall effect of wind on the flight of a bullet. Speed, direction and value all play a part. Speed is the easiest to figure out. Direction comes next. Value is the sleeper. If there is a 10 mph wind 90 degries to the firing line at the firing line, the bullet will start it's drift as soon as it leaves the muzzle. If the same wind is 600 yards down range, and the bullet only passes through it in the last 100 yards to the target, the 'value' of that wind is a lot less.

I'm still learning how to deciphering the conditions so bear with me, but I find that figuring out the wind velocity downrange, say at 800 yards from the firing line, is much more difficult than determining the wind direction, from which I can figure out the value on my trajectory. So my question to you is how do you determine the wind velocity (speed) downrange, yet still have a hard time figuring out direction and value.

quote:

Originally posted by NikonUser:

quote:

Originally posted by SgtGold:
The are numerous factors in determining the overall effect of wind on the flight of a bullet. Speed, direction and value all play a part. Speed is the easiest to figure out. Direction comes next. Value is the sleeper. If there is a 10 mph wind 90 degries to the firing line at the firing line, the bullet will start it's drift as soon as it leaves the muzzle. If the same wind is 600 yards down range, and the bullet only passes through it in the last 100 yards to the target, the 'value' of that wind is a lot less.

I'm still learning how to deciphering the conditions so bear with me, but I find that figuring out the wind velocity downrange, say at 800 yards from the firing line, is much more difficult than determining the wind direction, from which I can figure out the value on my trajectory. So my question to you is how do you determine the wind velocity (speed) downrange, yet still have a hard time figuring out direction and value.

I usually use range flags. Each firing line had at least one so you can gauge speed direction, and value. There are tall reeds and other foliage that you can read off as well. One downside is the last 150 yards to the target is a lake, and that kinda kills reading the mirage. It's not like shooting in the desert or on a well manicured range like Perry.

I should have elaborated a bit on partial wind conditions. The range I shoot high power on is one of the worst ranges in the US for consistency as far as wind goes. The wind enters the valley from two directions at once, then swirls a bit just to screw with you. From 200 and 300 it's not that difficult to read the conditions, but the 600 yard line is elevated about 30' and offset a few degrees to the west. The wind you shoot through is not the wind the flags see. You can end up with two or three different wind conditions on your way to the target, and each one has a different value based on how far from the target they are.

As to where mistakes come in it's in not seeing how wide a footprint the wind condition is effecting. If you have two flags 100 yards apart flying in different directions, where is the exact boundry between the different wind values? Does the wind shift direction just behind the 300 yard flag, or right in front of the 200 yard flag? This is what makes this sport interesting. If I always shot in completely predictable conditions, I'd be a high master in everything.

I see. I'm just a little quizzical on how you can read the velocity of the wind more accurately than you're able to get the direction of the wind and value from the same flag.

I travel to a lot of ranges for competition and I find that each range has its own claim to fame for some aspect or another.

I usually find that mirage + flags are a good way to go, but interpreting mirage can be tricky. Especially when the mirage goes one way and the flags go the other way.

OK, playing the game, and blindly believing in my Ballistics AE smartphone app

For a 6mm Creedmoor round out of the wife's rifle, shooting to 1775 yards, in a windless environment and ignoring Coriolis Acceleration, the horizontal deflection ("wind hold") would be .5 mil, to account for spin-drift.

Positioning two wind sources at 100yds and 111yds blowing perpendicular at 100mph (air boat prop wash, no idea how realistic my wind speed pick is, but I'm playing), yields a required wind hold of -21.55 mil, or a total required correction of 22.05 mil.

Rerunning ballistics with the same wind sources moved to 1502 yds and 1514 yds results in a wind hold of -16.7 mil, or 17.2 mil total deflection.

Which goes to show that wind exposure in the early phases of bullet flight will have greater impact than later in flight.

To help with the math: 22.05 mil at 1775 yds are approx. 1409 inches, or 117 ft. The difference between positioning the "wind" at 100yds vs. 1500yds is a change in wind deflection of 310 inches.

(I have no idea how Ballistics AE models "point wind sources" in its advanced wind setup. I have no idea how fast the prop wash from an air boat is. I'm sure real-world results will differ from what I outlined above. I also know that 1 mile is 1760 yds, not 1775 )

quote:

Originally posted by NikonUser:
I see. I'm just a little quizzical on how you can read the velocity of the wind more accurately than you're able to get the direction of the wind and value from the same flag.

I travel to a lot of ranges for competition and I find that each range has its own claim to fame for some aspect or another.

I usually find that mirage + flags are a good way to go, but interpreting mirage can be tricky. Especially when the mirage goes one way and the flags go the other way.

To put it another way many shooters can read a flag, but fail to take into account that the 4-6 MPH wind isn't blowing across the entire length of the range. They miss little signs and dial in to much or not enough windage, with predictable results.

One more thought to ponder, that actually may answer your original question better than the air boat experiment above:

Imagine ideal shooting conditions: constant wind across the full distance, no landscape features that could channel the wind, or change its impact on bullet path, and your ability to read/determine exact wind speed (which would be easy, as it's the same in your position, and across the full mile between you and the target). You have the perfect solution from your ballistics tables. You pull the trigger.

A microsecond later, wind speed increases by 1 mph. Again, conditions stay ideal: wind speed is the same across the full mile, no unusual landscaping to affect the bullet. You didn't pull the shot.

Using data for my load (6CM, 108gr bullet), at this location (elevation approx. 5000ft.), impact on the target 1 mile away would shift by roughly .4 mil, or 2 feet. Effects at sea level would be greater than at my altitude. Quite significant, if you ask me.

quote:

Originally posted by Rotndad:
The Shooter Mark Wahlberg explains that a shot at that distance takes in to affect (effect, I can never get this right)

Would take into account work here? Anyways, my question, is there any one, good book that explains everything that influences bullet trajectory and how to adjust for them? The Ultimate Sniper, perhaps?

I believe the Litz books do a great job

"the Litz books": https://store.appliedballistic...hResults.asp?Cat=103

Applied Ballistics for LR Shooting, 3rd edition covers "external ballistics". Accuracy and Precision looks at Precision, Accuracy and Weapon Employment Zone analysis, i.e. takes it beyond external ballistics to include the weapon system and the shooter.