shooting in the rain

[Dr. Tad Hussein Winslow]

I do find it extremely odd that even heavy rain doesn't materially change the point of impact. You would think it would knock your bullets down, and have a much lower point of impact. It does cause some erratic shots, and hinders accuracy. But overall, accuracy can be acceptable in the rain, provided the wind is not crazy.

 

[EShell]

I will very quickly agree that the facts are counterintuitive to what we would all assume.

I would also venture yet one more potential explanation for drop blamed on rain that I had forgotten to mention above: Vertical spin drift due to crosswind. In rainy weather, prevailing winds often reverse, which *will* have a very pronounced effect on trajectory.

How many here are aware that at longer ranges, 1,000 yards for example, a left wind of even 5 to 10 mph will drive a bullet downward as much as 1 to 2 FEET, and that a right wind of the same value will raise impact?

Not to be argumentative, but, when it comes to this subject of a bullet "beating it's way through rain" theoretically slowing it and making it drop noticeably more, fact and field observation seem to contradict our shared intuition.

I too had "thought" that rain would slow down the bullet as it plowed through an infinite number of raindrops on it's way to the target. I came to see that I had been mistaken, based on both my own experiences and the experiences of other long range shooters. While we, due to the refresh rate of our eyesight, perceive rain to be "streaming" downward, it is actually a series of discrete droplets that may or may not be intersected by any given bullet on it way to the target.

The technical explanation has to do with the forward shock wave displacing any raindrops prior to the bullet's arrival. Erratic flight would then, by necessity, be caused by some other factor, since the bullet *never touches* a raindrop.

Intuitively (again), I would suggest that we cannot get something for nothing, and that a certain amount of forward inertia *must* be sacrificed to "move" the (minuscule) mass represented by raindrops, but, in practice, this minute amount of inertia lost is very small in comparison to the bullet's kinetic energy. So small as to be completely buried in the "noise" and not worth factoring into any trajectory equation.

The obscuring "noise" consists of variations in muzzle velocity, aiming error, trigger control, crosswind, bullet weight and meplat shape.

Just taking muzzle velocity as an isolated example, we have both constant shot to shot variation and an overall reduction in MV upon temperature drop.

So, if we shot yesterday at 85oF and zeroed at 1k, but today (it's raining and) our ambient temps are down 10o, to what do we attribute the extra drop?

Many people shoot loads that exhibit extreme velocity spreads of 25 fps, even 50 fps. Only 25 fps MV with a 175 SMK at .308 velocities (2,600 vs. 2,575 fps) equates to over 8" difference in drop at 1k - actually quite a bit of "noise".

LOL, as minor as it may seem, it has been conclusively proven that uniforming (trimming) meplats provides more consistent long range performance by reducing vertical variations due to bullet shape (BC) differences. The same experts that agree that this step is worth the time, effort and tool costs tend to disregard the effects of rain. Who here trims their long range bullet noses? Not me. . .

I *will* find and post the extensive military study that *proves* that rain's effect on bullet flight is not worthy of consideration in our context.

 

[General Geoff]

The technical explanation has to do with the forward shock wave displacing any raindrops prior to the bullet's arrival. Erratic flight would then, by necessity, be caused by some other factor, since the bullet *never touches* a raindrop.

This is simply incorrect; the shockwave created by a bullet is generated by the tip of the projectile, not some imaginary point in front of it. If a rain drop is in the way, the bullet's going to hit it. The shockwave will not somehow shelter the bullet from the water, any more than a bullet fired into a pool.


Even if the drop of a particular round in heavy rain is negligeable, that doesn't mean that it's displacing the rain with some sort of voodoo precursing shockwave. It just means the few rain drops that it strikes on the way to the target don't have a profound effect on its ballistic path.

 

[30Cal]

From what I've seen, it has no effect, at least until the target becomes heavily obscured.

 

[taliv]

even in a frog-strangler, the odds of hitting a drop would be quite low

 

[EShell]

This is simply incorrect; the shockwave created by a bullet is generated by the tip of the projectile, not some imaginary point in front of it.

If you say so . . . but what I see is not at all imaginary:


Less obvious here, but still barely discernible:


Here's another:


This is my own favorite:

 

[packnrat]

i hate the rain...

try needed glasses and it starts to rain. very hard to see much of anything.

frend or foe. can not tell....maybe that was just a tree......





.

 

[MTMilitiaman]

Anymore, time and opportunity for me to go shooting is so rare that Hades himself couldn't stop me. I'll shoot in the sun, rain, or snow.

 

[BammaYankee]

Taliv raises an excellent point...

Many on this forum talk about what they would do in which situation using this gun and that ammo. Many others talk about shtf, disaster scenarios, etc etc. Well, what if these situations really do come to pass, but it's not 70 degrees, sunny, with no humidity when it comes time to use your gun?

I have competitively shot & hunted in the snow, feezing rain, and the sweltering heat of the deep south and it really does challenge one's shooting ability! No one would say it is fun, but I think it is good experience.

How can anyone on THR seriously discuss or prepare for situations that may require putting one's gunmanship to the test without at least experiencing less than ideal shooting conditions? To me that is down right irresponsible!

 

[Bartkowski]

It seems that EShell has lots of experience and knows many others with similar levels of experience, whereas General Geoff is just saying what he thinks is true. I haven't shot very long distances, but I have shot in the rain and have not noticed any effect.

 

[jjohnson]

Rain, Snow, Dark of Night

Well, I'm not sure I like shooting in foul weather just because I like the weather that way, but:

1) The range definitely empties out in bad weather.
2) If other people ARE there, they're the serious shooters, not Mall Ninjas such.
3) Ya know, when you HAVE to shoot, it's probably not going to be in your choice of weather, anyway, so you may as well get in proper training.

 

[Funderb]

the effect is humidity, not rain, humidity greatly affects bullet traj.

 

[Howard Roark]

I've shot high power in the rain several times. 600 and 1000 yards. I had no elevation changes. I did blow a lot of primers due to increased chamber pressure.

 

[EShell]

the effect is humidity, not rain, humidity greatly affects bullet traj

Well, not as much as one might think, and probably opposite what one would *think*.

Of the major environmental factors affecting trajectory; barometric pressure, temperature, altitude and humidity (the combined effects of which accounted for in density altitude), humidity is one aspect actually not worth calculating. When humidity increases, H2O actually displaces heavier/denser atmospheric components and net air density declines. When air density declines, drop is reduced, yet another counterintuitive concept that was traditionally misunderstood even by the US military. The military has since revised doctrine to reflect scientific truth, our goal here.

The reason air seems "thicker" (and assumed more dense) when humidity increases is simply because we are air cooled beings, and we depend on evaporation to cool, which is impeded by excess atmospheric humidity.

If we calculate the drop of a .308/175/2,600 fps at 1,000 yards from a 100 yard zero at, say 10% humidity, we arrive at 39.4 moa (Sierra Infinity). If we change nothing else but increase humidity to, say 95%, and rerun the numbers, we now have only 39.3 moa.

Two things become apparent: First, the scant .1 moa difference in drop is yet another factor buried in the "noise" and so not worth fooling with, and second, increased humidity results in decreased drop . . . go figure.

I realize that this too is not what is expected, but is what happens, and I would again suggest that other unnoticed factors would be responsible for any change in drop that would seem attributable to humidity.

 

[taliv]

not to pick nits in my own thread, but wouldn't that make us water-cooled?

 

[MGD 45]

Well, I have shot my .308 168 gr. BTHP in the rain to collect data for my sniper log book. Of course, on the day it was raining I was only able to shoot out to 100 yards. The rain had no effect what so ever on the bullet dropping. It did however rise up 1/2 an inch in height from POA to POI. However, I contributed this to a drop in Pressure in the atmosphere.

Now, the rain was more like a steady light rain vs. a heavy fat downpour.....

 

[telomerase]

How can anyone on THR seriously discuss or prepare for situations that may require putting one's gunmanship to the test without at least experiencing less than ideal shooting conditions? To me that is down right irresponsible!

Is it more irresponsible than keeping one's children in a country which is involved (via foreign aid) in every conflict in the world (usually on both sides), yet has no civil defense?

Responsibility is un-American, and I for one won't stand for it!

Well, OK... is it all right if I take an umbrella?

 

[boilingleadbath]

The photos you showed of bullets with notably detached bow shocks were scarcely supersonic - if you look at the rifle bullet, you'll notice that the bow shock is pretty much ON the point of the bullet.

Besides, I wouldn't expect those shocks to move the rain very well.

However, that doesn't mean the rain effects the bullet. Let's do some math.

Lets say that:
the rain storm drops one inch of rain in two hours
a raindrop is 1/100th of a ml (pretty small for that type of rain, I'd expect, but we are being cautious here)
those raindrops fall at 25 mph
That those raindrops are infinitely small (makes them hard to hit)
That you are shooting a .3" diameter bullet
At 1000 yards

So, the flight path of the bullet has a volume of 41,000 cm^3
And a cubic centimeter of air contains 2.85*10^-5 raindrops at any given point in time
So the average bullet encounters 1.2 raindrops on it's way to the target... over 1000 yards... in an incredibly dense rainstorm of unusually (?) small raindrops.

I can't find my stats notes righht now, so I can't tell you the probability that the raindrop will hit 0/1/2/... raindrops.

 

[Dr. Tad Hussein Winslow]

Good analysis, Ed - thank you.

 

[oldgold]

I ran and shot in a .22 silhouette match for ten years. We had a nice covered shooting building so matches were held regardless of the weather. Many matches were held in the rain. I never noticed any effect the rain had on point of impact. Many of our top scores were posted in a light rain.

Back in the sixties I broke my first 50 straight at trap in a driving snow storm. I was so cold and miserable I was not keeping score in my head. Just wanted to get inside. Shoot, shiver and shut up?

 

[EShell]

not to pick nits in my own thread, but wouldn't that make us water-cooled?

Good question.

The photos you showed of bullets with notably detached bow shocks were scarcely supersonic - if you look at the rifle bullet, you'll notice that the bow shock is pretty much ON the point of the bullet.

Point taken, but, it sure did appear that we were suddenly dealing with absolutes, and ALL of the pics suggest that the shock wave does precede the bullet, albeit to a greater or lesser extent.

Regarding degrees fo supersonic flight, FWIW, most .308 bullets (an easy to reference and well known set of ballistic data) are near trans-sonic at 1k anyway, and some, like the 168 SMK, often go completely subsonic even before 800, depending upon density altitude. Of course, as soon as we go trans-sonic, the front shock wave collapses and the rear shock wave and turbulence overtake the bullet.

Besides, I wouldn't expect those shocks to move the rain very well.

"Move" or "vaporize"? All we need to do to negate influence is to reduce density to something less than "water". The reason I would suggest "vaporize" is that the bullet trace is often quite evident on rainy days, resembling smoke . . . or vapor. Simple displacement would cause no appreciable change in trace, which is often visible even on a sunny day.

So the average bullet encounters 1.2 raindrops on it's way to the target... over 1000 yards... in an incredibly dense rainstorm of unusually (?) small raindrops.

I defer to your statistical analysis, but will maintain/agree that rain has very little to no effect on bullet flight, my original premise.

 

[Hoplophile]

"Never really did much target shooting in the rain, but I've sat in my share of tree stands during downpours. Deer usually bed down when there's a frog-strangler, but when the rain stops it is good to be on the stand. I usually try to sit it out unless there's no end in sight. I usually carry one of those plastic rifle bags for my gun in case it starts raining. What do you guys do about rust?"


...Wow, someone used the term "frog-strangler". Thought I was the only one.

 

[wanderinwalker]

My first season of competitive Highpower shooting, we shot a match in the mid-40s-low-50s and drizzle/rain, in May. Gotta love New England weather! Actually, I didn't think there was any other way to shoot a Highpower match by the time we were through the spring and early summer that year. It just didn't seem right if my AR wasn't spitting water on my with every round!

Honestly, I've never noticed enough POI/POA shift in rain or snow to worry me, especially out to ranges you can still see a target.

Actually, back to my first HP season, I used to practice in February when I had to shovel out a firing point through the snow drifts. If you can shoot well at 20 degrees, fingers and toes out of contact, in blowing snow, rain in July is easy.

I have also fired many rounds of 9mm down into the single-digits, and can assure you that ammo just barely powerful enough to cycle at 60-70 degrees, will likely give you some issues at those temperatures. Boost things into a more normal spec, and you'll be fine.

 

[taliv]

oddly enough, almost all of my HP shooting has been in 90* or higher sun. i can only remember shooting one rapid fire string in the rain.

i can't imagine shooting HP in the snow.

 

[boilingleadbath]

"'Move' or 'Vaporize'"

I'm not sure it's consequential - ultimately, even if the bow shock breaks up the raindrop, the mass is still there, and has to be moved.

I don't know enough about the situation to be able to tell if moving that mass is:

1) Even possible through purely shockwave effects deflect the rain
1B) Going to produce unbalanced loads on the bullet even if it is.

#1 is a complete unknown to me. I'm kindof doubting it, given how THIN shockwaves generally are, but I have no formal or informal training in the matter.

As for as #1B goes - it certainly possible that the shock redirects the "increased density zone" that was formerly the raindrop without communicating any (as much) force to the bullet... but again, I know very little about shocks.

******

I'm not doubting your conclusion that rain doesn't affect bullet flight to any appreciable degree.

******

Anyways, lets look at a more-or-less worse-case scenario, were the raindrops aren't influenced by the shock at all. How much will the rain deflect the bullet?

Bullet is assumed to be 10 grams, 2500 fps, with a conical front .6" long and .3" in diameter, and it hits a .01 gram raindrop.

Again, I have no formal fluid dynamics training, so I'm just doing calculations which seem reasonable to me.

Let's assume that when the bullet impinges on the water, the force is normal to the face of the bullet. Further, let's ignore the deflection of the water drop and bullet. So they are both essentially frictionless points/surfaces.

The inverse tangent of the angle perpendicular to that of the bullet's cone is 4. So I think the raindrop will acquire 4 times as much sideways movement as forwards movement.
And the raindrop has to acquire a sideways velocity equal to 1/4th of it's relative velocity.

If I did my physics right...
For the raindrop:
deltaV.radial = 606 fps
deltaV.axial = 75 fps

Of course, divide by 1000 because of the weight difference, and you get .6 and .075 fps change to the bullet's velocity.

Which, even compounded over the 1.5 second flight time, isn't very significant. (though I'm sure it is an inaccurate idea to ignore the other aspects that result from bumping a bullet.)