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The Effect a Raindrop Has On a Bullet

by Win_94
Tags: bullet, effect, raindrop
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Win_94
#55
Mar24-13, 09:57 PM
P: 35
Another thing, the point of aim must be constant. The first test had the same point of aim even though I intended to hold for wind; which I understand now would have been a mistake.

So either viewing the wind flags will need to be part of the video, so one can see how the wind is affecting the shots; or only the size of the groups should be taken into account.
In other words, noting the water impact's proximity to that of the non water hits, would be irrelevant due to the probability of differing conditions.

A 10mph wind from 9 o'clock at 200 yards drifts 3.8 inches. That is about the same drift as the 6mph wind from 10 o'clock in the earlier 300 yard test. So wind at 200 yards is greatly reduced, but still a factor.
OmCheeto
#56
Mar24-13, 10:03 PM
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Quote Quote by Win_94 View Post
I don't know if you're messing with me or what. I have no idea what that means.
He's not messing with you. His laugh was at himself.
"Paint" is the poor mans doodle tool for PC's.
Many turn their noses up at it.
I use the mac version.

His doodle is a graphical representation of the target area experiment I described.
The more water the bullet comes in contact, uni-laterally, the larger the deflection.
Win_94
#57
Mar24-13, 11:16 PM
P: 35
Quote Quote by OmCheeto View Post
He's not messing with you. His laugh was at himself.
"Paint" is the poor mans doodle tool for PC's.
Many turn their noses up at it.
I use the mac version.
Yes I get the "paint" reference; I just didn't understand the drawing.


Quote Quote by OmCheeto View Post
His doodle is a graphical representation of the target area experiment I described.
The more water the bullet comes in contact, uni-laterally, the larger the deflection.
Ok, I understand what he means now... but trying to hit a single drop is what I need to try for. Because even in a heavy rain, the odds of hitting a single drop is great.
So are you implying that I need to hit more water than one drop? A single drop hit, two at the most is what I need to attempt for the experiment to be consistent with moderate to heavy rain shooting conditions.

I'm confident I'll hit the drops I need to.
Aero51
#58
Mar25-13, 12:21 AM
P: 546
From an aerodynamics stand point there are a few things to take into account

1) The raindrops do not change the macroscopic shape of the projectile
2) They will "wet" the surface with a microfilm of drops and water
3) The mass of the bullet will increase slightly

These three properties lead me to the following conclusions:

1) The form drag and induced drag will not be changed. In other words, drag due to separation of the air from the surface of the body and drag due to lift created by the body will not be affected by the rain.

2) If the mass increase is non-negligible, then the rate of rotation of the bullet will decrease proportionality to conserve angular momentum. This will decrease the overall accuracy and stability of the bullet.

3)This leads me to the conclusion that the raindrop and moist air will increase the skin friction coefficient of the bullet (or drag due to the air shearing over the surface) and result in a lower average velocity and a decrease in trajectory.
mfb
#59
Mar25-13, 04:31 AM
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@Win_94: A single drop hit is fine, and I don't see where multiple hits were mentioned here. What my graph is describing: Not all tests "with water" will hit a drop, so you have some shots without a hit (giving a narrow cluster of impacts at the target) and some with (giving a broader distribution).
I am not really convinced that the camera can accurately see the hits, so it is good if the study can give results even without that information.
mikeph
#60
Mar25-13, 05:09 AM
P: 1,212
A tracer round in low light with a long shutter speed camera placed behind the gun might capture it. E.g. if the bullet is deflected downwards, a camera positioned at the same height but ~1m to the left/right of the gun should give you an angled trajectory. Might be tricky to get a deep enough depth of field.


mfb- I don't see how the distribution approach will work, hitting the water is not binary, some bullets may glance a droplet and be slightly deflected, and those glancing bullets will form a distribution with an intermediate half-width.
mfb
#61
Mar25-13, 05:11 AM
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Quote Quote by MikeyW View Post
mfb- I don't see how the distribution approach will work, hitting the water is not binary, some bullets may glance a droplet and be slightly deflected, and those glancing bullets will form a distribution with an intermediate half-width.
They are all part of the broader distribution. That is the reason why this is a broad distribution - the details of the impact vary.
A.T.
#62
Mar25-13, 05:58 AM
P: 3,899
Quote Quote by DaleSpam View Post
This would be an awesome Mythbuster's episode. Especially with the high speed camera.
In the below video at 2:00 the bullet collides with some white balls, which disintegrate like a fluid, but seem solid before impact. They move faster than the bullet. What could that be? Lead?

mikeph
#63
Mar25-13, 06:35 AM
P: 1,212
Quote Quote by mfb View Post
They are all part of the broader distribution. That is the reason why this is a broad distribution - the details of the impact vary.
Gotcha, I think my brain stopped working when I wrote that.
Andrew Mason
#64
Mar25-13, 12:49 PM
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Quote Quote by A.T. View Post
In the below video at 2:00 the bullet collides with some white balls, which disintegrate like a fluid, but seem solid before impact. They move faster than the bullet. What could that be? Lead?
It is likely bullet lead (an alloy containing trace elements of antimony and other metals). The high speed impact creates an enormous pressure within both bodies. Since this pressure deforms the metal bodies, they heat up (think of the pressure multiplied by the volume change as energy added to the body). When they heat up enough, the metal melts and, because of the pressure, explodes into tiny fragments.

AM
Win_94
#65
Mar28-13, 02:28 PM
P: 35
Here are the results from the second test.

http://www.youtube.com/watch?v=UusiTSu1tSU

Specifics:
Howa 1500 30-06
Hornady 150gr FMJ, 2600fps
Varget 46.6gr
CCI 200
Winchester case
300 yards
Dropper devise 260 yards from target

Shots 3, 4, 5, 6, 8, and 9; hit water drops. They make an 8 inch group.
Shots 1, 2, 7, and 10; did not hit drops. They make a 1.5 inch group.
The group that hit water drops, is over 5 times the size of the group that didn't.

Note:
I thought shot 8 missed a drop, otherwise I would have taken shot 9 without water as I did shot 10. I couldn't see the water hits on the camera so I speculated from the POIs on how many hits on drops I had accomplished.

I think it is obvious that a raindrop can affect a bullets trajectory.
mfb
#66
Mar28-13, 03:04 PM
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P: 11,576
Thanks for the test. The result looks very nice.
Win_94
#67
Mar28-13, 03:39 PM
P: 35
Quote Quote by mfb View Post
Thanks for the test. The result looks very nice.
You're welcome! I'm glad now that I did another test; it was much better the second time around.
mikeph
#68
Mar29-13, 04:56 AM
P: 1,212
I'm convinced! I wonder why most of the hit bullets end up higher on the target. Must be a random fluke, hitting water droplets on the top half more than the bottom? I'd expect the hits would end up lower if they lose speed during the collision.
Win_94
#69
Mar29-13, 11:05 AM
P: 35
Quote Quote by MikeyW View Post
I'm convinced! I wonder why most of the hit bullets end up higher on the target. Must be a random fluke, hitting water droplets on the top half more than the bottom? I'd expect the hits would end up lower if they lose speed during the collision.
I think it is a random fluke. The other test has one low hit, then the first video has a 2 low hits if you consider I aimed high on the second shot. But yes, it is odd there weren't as many low shots or more.


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