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Effects of rain on bullets flight?

2K views 27 replies 26 participants last post by  russel5150 
#1 ·
I'd like to know what effect can have the rain - from light to the heavy one - on the bullet flight behavior. I did a research in my books and on Internet, finding only an Internet thread referring to Gen. Hatcher's work; but I have its beautiful "Notebook", and I didn't find nothing there about the argument.
Would you so kind to help me in my research?
TIA,
Maxm
 
#3 ·
I doubt any realdata exists. Too many variables. How big are the drops, how fast, how close together. Wind can be quantified. Direction and speed. There are even tables out there. I do not think that you could come up with anything usefull for rain. Wind 15mph from SW objective. Rain, how hard and drop size subjective.


Len
 
#4 · (Edited)
You would think the military would have some sort of data. I'm sure snipers take everything else into account, wind speed, direction, temperature, anything that can effect trajectory. If rain effects bullet travel, they would probably know. Even if data is subjective, or can't be quantified, it doesn't me there is no effect.
 
#6 ·
First thought: Impacting the droplets absorbs energy from the projectile. Since the impacts would be random (at all/any points on the ogive), the principal effect would be reduction of velocity. This reduction most likely would be minimal at ranges to 300M, but would begin to accumulate beyond that.
Second thought: The shock wave at the nose of the bullet may prevent it from actually touching any droplets, so velocity reduction may be extremely minimal.
 
#7 ·
Here's a link to the US Army sniper field manual. No mention is made of rain effects, but other environmental conditions such as altitude, humidity and wind are treated in some detail. If rain has a measurable effect, I would think it would have been addressed. I'll be surprised if it turns out that it does not have some significant effect since things like humidity do. I find it odd that the Army does not address it in the manual, but maybe I'm wrong and the effect is truly negligible.


http://www.globalsecurity.org/military/library/policy/army/fm/23-10/ch32.htm#s3p6
 
#9 ·
Pretty much irrelevant, but I'll add it any way...;)

I've seen paintballs do some weird things in the rain. Basically, their very inaccurate. However, I don't know if the rain effects the ball itself or if the water effects the barrel ports causing the problems.
 
#11 ·
If you calculate mass/velocity/vector of raindrop(s) vs mass/velocity/vector of bullet, the effect is nil at normal handgun ranges. More effect for lighter bullets, more for lower velocity...

Doc H. :cool:
 
#12 ·
When humidity approaches 100%, air density is greater. That will affect velocity but only nominally. The rain's affect on barrel temperature may make a small difference. In rainly conditions, compromise to human variables such as visibility (as mentioned by mike'sgooddeal) and shooter control may have a much greater effect.
 
#13 · (Edited)
Raindrop size is really a statistical distribution of sizes in a particular storm. The size distribution can be determined using a disdrometer, a device measuring rain impact. A general sense of the distribution can be found using measurements of radar scatter. Once the size distribution is determined, the terminal velocity of the average raindrop can be calculated.
Terminal velocity is a function of raindrop diameter:

Drop Diameter, mm -----Terminal Velocities, ft/s (from Lenard)
0.5--------------------11.5
1.0--------------------14.4
1.5--------------------18.7
2----------------------19.4
3----------------------22.6
4----------------------25.3
5----------------------26.2
5.5--------------------26.2
6----------------------25.9
6.5--------------------30.2

Now comes the first of the REAL problems: determining the spacing between the drops and the probability that the bullet is hit by a drop. If that can be determined, then you can sum the forces of the raindrop impact with the forces associated with the movement of bullet out of the gun in a vector summation. But, as suggested in another post, a bullet moving at 1000 ft/sec (681.8 mph), is moving close to the speed of sound and therefore should have a shock wave that would displace the raindrop, perhaps causing the drop to miss the bullet altogether.
What we can see is that the largest drops move at a velocity of 3% of the velocity of the bullet (30 ft/sec/1000 ft/sec) and therefore should have little influence unless the bullet is hit by many raindrops.
The question remains: if you run to get out of the rain, will you get more or less wet than if you walk?:scratch: :D
Ron
 
#15 ·
Trigger Creep said:
When humidity approaches 100%, air density is greater. That will affect velocity but only nominally. The rain's affect on barrel temperature may make a small difference. In rainly conditions, compromise to human variables such as visibility (as mentioned by mike'sgooddeal) and shooter control may have a much greater effect.
I don't think this is the case. Water vapor is less dense than air. This is why low pressure areas indicate a storm or one brewing and high pressure areas are clear.

I do have one experience in this area. Many years ago I helped run a three gun match at a local club. After we had set up the rifle stage (steel plates out to 250 yds) we tried them with our .45s. I was having pretty good luck out to 200 yds, hitting perhaps half of the time.

The day of the match was as moist as it could get without actually raining. Moving your hand rapidly through the air would cause water to condense on it. The match was shot wearing your pistol rig throughout all of the stages.

As luck would have it, the extractor on my M1A broke in the early stages of the rifle event. Since I had a pistol and about 40 rounds of ammo, I finished the match with the .45. I did OK at 100 yds but couldn't hit a plate at 150 or 200 yards, and ran out of ammo before I got close to engaging the 250 yd plates. A friend who was atching me closely later told me that everything seemed to be on target or close but low. I know this isn't a scientific observation, but is seemed like the moist air was offering a little more resistance to the bullets travel than clear, dry air. Perhaps the large diameter of the .45 bullet and its relatively low velocity (900 fps) were factors.
 
#17 ·
Hey there, Gammon. Yes, water vapor is lighter than air at standard temperature and pressure, but when it's raining the water isn't vapor any more. It has condensed into a liquid, which is denser than air. Almost as dense as me sometimes. Nevertheless, I doubt it makes much difference one way or the other.
 
#19 ·
RonC said:
The question remains: if you run to get out of the rain, will you get more or less wet than if you walk?:scratch: :D
Ron
Mythbusters did this one. According to them you get wetter if you run (BARELY).
 
#21 ·
I have shot smallbore competition rifle for years. At 100 meters, I did not see any effect on a .22 bullet due to rain, with that said. When there is rain there is wind and that will effect the bullet to a large degree.
 
#23 · (Edited)
Figure out what the chances of even having a drop of rain in the bullets path.
I remeber doing it by simulation with various drop sizes and rainfall rates years ago.
The odds of a rain drop and the bullet being in the same place at the same time are vanishingly small until the rainfall rate gets huge.
Anything acting on the front of the shock wave can have an effect on the object travelling at supersonic speed. At supersonic speed the control surfaces of an airplane are moving the shock waves, and the forces required are huge.

Just to get you thinking, a .22 diameter bullet sweeps out a volume of about 140.5 cubic inches per 100 yards traveled, or a cube about 5.2 inches on a side. During the bullets flight what do you think the odds of finding a drop of rain in that volume is? Remember flight time is in tenths of a second per 100 yards.
 
#25 ·
One reason rain is not factored into sniping is the simple fact that a light drizzle will to all intents and purposes obscure any target much beyond 300 - 500 meters, if you can't see it, you can't shoot it. Humidity and temperature and wind has the most effect on the flight of a bullet.

There is some paper on the effects of rain on a bullet at extreme range, but it is more a mathematical discussion, than one that has any real value, I do believe it was a group of extreme range shooters in Scotland that were involved in it, they had a nice website several years ago, but I can't remember the name of it, I will look to see if I still have it bookmarked on my old laptop..
 
#26 ·
What I have heard from long range benchrest shooters is that rain will open groups up a little. What truth there is to that I cant say. To them though a little is a lot more precise than I can shoot. I also remember hearing that the little .17HMR shows a vast opening of a group when shot in a decent rain. Here the thought behind it was that the little bullet was pushed off course by the rain much easier than a heavy bullet. Again I have no proof to back any of these claims up but it was what I have seen written. It could just be shooters not paying as much attention and needing something to blame group size on.
 
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