Rain affecting bullets

[MarkCO]

There are two questions really.

With a moderate speed .308 match bullet, humidity going from 0% to 100% will equate to 1.5 to 2" difference in drop on the bullet at 1000 yards. In reality, it is minimal, but it does have an effect.

With a .22 caliber match bullet, the difference at 1000 yards is on the order of about 1 inch. Still not a huge affect.

As for actually hitting a rain drop, not going to happen while supersonic. The air at the tip of the bullet is heated and is a laminar wake. Displacement and sublimation of the rain drops occurs making actual contact with the bullet a mathematical improbability so high that it should not even be considered.

Testing has shown that air loaded with water (high humidity) has beneficial fluid dynamic properties to a bullet in flight. Shooting in 50% or higher RH will actually produce slightly smaller groups than perfectly dry air.

Wanted to add this. High humidity does very minimally reduce the MV at which the bullet leaves the bore, on the order of a few fps. But once we leave interior ballistics and go to exterior, the humidity is beneficial.

[Ricklin]

We shoot trap in the rain every now and again. Seems to have no effect at all on the shot. Has a great effect on the shooter tho.

The rain seems to do nothing and we have lots more, lots smaller projectiles and they are traveling far slower. Say 1100-1200 FPS vs. 3000 FPS
Now the wind.....that's a different story.

[Brian Pfleuger]

Originally Posted by MarkCO

As for actually hitting a rain drop, not going to happen while supersonic. The air at the tip of the bullet is heated and is a laminar wake. Displacement and sublimation of the rain drops occurs making actual contact with the bullet a mathematical improbability so high that it should not even be considered.

Technically true but it's sort of a distinction without a difference. Since the bullet is producing the pressure wake, anything that effects the wake will also effect the bullet. In other words, if the wake in front of the bullet "vaporizes" a water droplet, the energy source is the bullet.

The actual effect may be slightly different, if the bullet actually hits the water directly rather than being "shielded" by the wake but whatever energy gets transferred to the water can only have come from the bullet, meaning hitting a water drop will slow it down and/or deflect it by some amount.

I agree that the odds are astronomically small but the effect would be real if it happened.

There are videos that show a rain drop getting hit:
https://www.youtube.com/watch?v=HWSES47YkyM

[MarkCO]

Heated air, enthalpy of vaporization of water...If you choose to actually run the equations, you can see how the humidity, cooling, helps the bullet in flight, not hinder it. Yes the energy comes from the bullet, but it is already wasted in heating so vaporization of rain drops has no effect (unless you have a REALLY big rain drop).

I did the calculations in grad school and no, I am not doing them on the internet.

[B.L.E.]

The fact that you can see the target through the rainstorm is an indication that light rays made it to your eyes without hitting a single raindrop.

[kilimanjaro]

So, as long as you keep your powder dry, no excuses arise due to rain.

[Ralgha]

Originally Posted by Brian Pfleuger

Lots of analysis

Your calculation is not correct, you do not have the proper volumes involved.

The .308 bullet in question is .308 inches wide (diameter) so we will consider a plane that is .308 inches by 36,000 inches (1,000 yards). Any point on this plane will be struck by the bullet as it travels, to be completely accurate, we'd have to consider the full circumference of the bullet, but that's too complicated and would make it even more likely to hit a drop anyway.

Our plane has 36,000*.308=11,088 square inches of area. We will assume a rainfall rate of 1 inch per hour (quite heavy) and that gives us a total volume of 11,088 cubic inches of water on that plane per hour, or 11,088/3,600=3.08 cubic inches per second.

We will assume an average raindrop size of 3mm in diameter, which is probably a reasonable assumption since drops generally split when they exceed 4mm. That is 0.118 inches in diameter, or 0.059 in radius, which gives us a volume of 0.059^3(4/3)*3.141=0.00086 cubic inches per drop.

This means that each second, 3.08/0.00086=3,581 drops will pass through that plane. So, over the bullet's 2 second flight time, 7,162 raindrops will cross its flight path.

The math to calculate the probability of how many drops it will actually hit is quite a bit more complicated, but just from the number of drops, you can reasonably assume that it's going to hit quite a few of them.

Now, multiply that by 5 for the 5 inches per hour that the first analysis did (which is a hurricane).

[briandg]

I have now reached the point of saturation.too much rain and not enough coffee.

I would like to suggest that one of the sharpshooters here lay out a jug of trickling water, and put a dozen rounds through that stream with a 17 harm. Use backer boArds to record effects.

[James K]

I think folks are saying that the next time I shoot a 10" group at 100 yards I can't blame that rain cloud over the hill a mile behind me. Darn it, and it sounded like a good excuse!

Jim

[FrankenMauser]

I think folks are saying that the next time I shoot a 10" group at 100 yards I can't blame that rain cloud over the hill a mile behind me. Darn it, and it sounded like a good excuse!

Nope, but you can rest assured that if you talk about a 0.103" group here, there will be someone piping up with, "But that was just because of the 98% humidity! Do it again on a dry day!"

[g.willikers]

So, how many angels can actually dance on the head of a pin?

[B.L.E.]

Originally Posted by mapsjanhere

While rain doesn't do anything on shooting a small bullet short distances it's interesting in what it does to a high speed interceptor missile fired in a storm. At 6000 ft/s it looks like the nose is getting sandblasted, losing fractions of an inch in material.

I have heard that flying through a rainstorm can really chew up the tips of a wood propeller on an airplane.

[tobnpr]

The math to calculate the probability of how many drops it will actually hit is quite a bit more complicated, but just from the number of drops, you can reasonably assume that it's going to hit quite a few of them.

I've followed up to this point, and the calc's are simple and seem to be logical and correct to me...far as dispersion of the raindrops, and probability...

The rest is over my head. My son's an aerospace engineering major that does calculus for "fun"...maybe I'll run this by him

[ThomasT]

I was at the range one day when there was a very heavy rain storm. At 100 yards I could not see any difference in the group fired by my 30-06.

On the other hand while shooting a crosman model 1377 pellet pistol at 20 yards my group went from around one inch to over 5" with a moderate rain. As soon as the rain quit the groups went back to normal size.

So the bullet speed with a cushion of air ahead of it may be the difference. I'll leave all the math up to you brainiacs.

It always makes me smile when I read about guys wanting a stainless/synthetic rifle so they can hunt in the rain. Not me, if its raining I stay in camp and play cards. Contrary to popular opinion I am made out of suger and I will melt.

[FrankenMauser]

ratshooter,


As for rain impacting shooting...
This was at 100 yards, shooting PPU 5.56x45mm 69 gr "Match" ammo, in about 1" per hour rain with a 15 mph tailwind, after 45-50 minutes of rainfall, and the targets were nearly dripping off the backers:
(I shared this photo for other reasons a few months ago)



Five rounds stacked up for 0.347".
Number six more than doubled it, for 0.703".

Number six was ALL me. The rain had nothing to do with it.
...And still one of the best groups ever fired by that rifle.

(Point of aim was the blue globe on the right side. That load impacts ~3/4" left, for some reason.)

[ThomasT]

Nice shooting Frank. I have shot a few groups like that but not many. I just sight in and its time to go hunting.

I have some loads like that or at least close to that for my 243 using Hornady 100gr bullets. Nosler 100gr bullets will shoot close to that but slightly high and left. I have to resight to use the nosler loads.

As for shooting in the rain I just don't do it. That one time at the range with the 30-06 was just a fluke. I am a fair weather shooter no two ways about it. But it was an interesting experiment.

[kraigwy]

You really want to see the difference or lack there of, go to a HP rifle match during a rain storm.

I've been shooting high power for nearly 40 years (started in '77). They don't call matches for rain. The only one I ever saw called was the Short Range Team Match at the Wilson Matches in '78. There was a flash flood behind the pits, they weren't worried about the shooters but didn't want the pit crew washed away.

Anyway go to the match in a rain storm. You'll notice for the good (Master-High Master) shooter's scores don't change compared to fair weather days.

The rain does effect the newer shooters, (not bullets but shooters).

The main difference is the Masters/High Masters practice in the rain and every other conditions.

The rain drops aren't gonna disrupt the bullets.

[RaySendero]

kraigwy wrote:
.....

The rain drops aren't gonna disrupt the bullets.

The rain does effect the newer shooters, (not bullets but shooters).

Yep, Second that - This has been my experience, too.

Rain has not effected trajectory or accuracy for any of my rifles out to 500 yards.

[6.5swedeforelk]

ratshooter wrote:

...It always makes me smile when I read about guys wanting a stainless/synthetic rifle so they can hunt in the rain. Not me, if its raining I stay in camp and play cards. Contrary to popular opinion I am made out of suger and I will melt...

But the absolute best elk hunting/stalking is in the rain,
I would say to the tune of 400% better than sunshine.

[MrBorland]

Originally Posted by kilimanjaro

Denser air will slow the bullet and cause greater drop

It's counterintuitive, but AFAIK humid air is less dense than dry air: A molecule of water will displace a molecule of air, and the molecular mass of water is much less than the average molecular mass of air; ergo the mass of a given volume of humid air (i.e. density) is less than the same volume of dry air.

[B.L.E.]

It's counterintuitive, but AFAIK humid air is less dense than dry air: A molecule of water will displace a molecule of air, and the molecular mass of water is much less than the average molecular mass of air; ergo the mass of a given volume of humid air (i.e. density) is less than the same volume of dry air.

On the other hand, there is not as much water vapor in the air as many think there is. Air that has a 68 degree dew point, (100% relative humidity @ 68F) is only about 1.7% H2O by weight.
But, yes, water vapor is less dense than air. The reason a steam locomotive's steam whistle rises in pitch as it blows is because the heavy air in the whistle's resonating tube is being replaced by steam as it sounds a note, just like inhaling helium makes you sound like Donald Duck when you try to talk.

[Lwh4207]

Thanks for the answers guys. But I'm kinda having a hard time grasping all these formulas since rain is an uncontrollable variable.

[T_PRO_Z]

First off, I've never seen a difference between shooting in the rain, and shooting on dry days. The biggest issues I've had, are long shots during the middle of summer. The "heat waves" causing refraction can play hell with seeing your target.

Rain makes up 0.2% of air volume during a 2-inches-of-rain-per-hour storm. (With 0.016 gallons of water falling through a cubic foot {7.5 gallons} of air per second.) It makes up far less than that during normal rain storms.

You have a 1:500 chance of hitting water in a one cubic foot air space (2"/hour) during a 1 second time interval.

Remember - The human brain makes us see things that are not necessarily real. It may look like a wall of water, but it's a bunch of individual rain drops. The streaking is a processing effect, done by our brains, so we have time to "see" the rain - rather than the brain only acknowledging it subconsciously.

To look at the odds of hitting water, let's look at only the bullet's path.

Imagine the bullet will travel through a "cylinder" of air.
With a .308" bullet, we need to find out how long this cylinder will be, to have a volume of one cubic foot.

1 Cubic Foot = 1,728 Cubic Inches
The volume of a cylinder is calculated as:
Pi*radius^2 (of circle)*length (of cylinder)

The radius of a .308" bullet is .154".
Pi(3.141)*.154^2 = 0.234 square inches.

1,728 cubic inches / 0.234 sq in = 7,382.5 inches

So, a .308" diameter cylinder needs to be 7,382.5 inches long to contain one cubic foot of volume. (7,382.5 inches / 12 inches per foot = 615.2 feet)

Which means.... your .308" bullet can travel 615 feet or 205 yards with a 1:500 chance of hitting water. Move closer to the target, at 100 yards; and you have a 1:1025 (0.0975%) chance of hitting water.

If it's only raining 1"/hour ... those odds go to 1:2050 (0.0488%) at 100 yards.

And that's not even figuring the adjustment for bullet flight time. Most bullets won't take a full second to reach the target. Therefore, they won't have a full second's worth of exposure, and the odds of hitting water are decreased even further.

For example (simple calculation with constant velocity):
A 2,100 fps bullet will reach a 100 yard target in 1/7 of a second (2,100 feet per second/300 feet = 1/7 second).
That means the odds of hitting water drop to a 1:7175 (0.0139%) chance of hitting water.

the above quote is from Frankinmauser's previous post on the subject^^^

I have gotten the information in bold letters from google, the rest of the calculations are ones that I have done:

The volume of a sphere is 4/3 * 3.14 (pi) * (d/2)^3 [that last term
is the radius cubed]

So the volume of a small drop is 4/3 pi (.01)^3
= 4/3 * 3.14 * 10 ^-6 [that last term is one-millionth]
= 4.2 * 10^-6 cubic inches
And the volume of a big drop is
4/3 * 3.14 * (.1)^3 [that last term is one-thousandth]
= 4.2 * 10^-3 cubic inches
my calculations:

A 1-foot cube is 12 x 12 x 12 = 1728 cubic inches.

So it takes 1728/(4.2 * 10^-6) = 412,700,000 little drops
or
1728/(4.2 * 10^-3) = 412,700 big drops to fill the cubic
foot.

A heavy storm provides about an inch per hour of rain, so the cubic
foot is about 12 hours worth of heavy rain. this is assuming you are getting 1" and hour

Therefore the odds of filling that cubic foot with water in the time it would take the bullet to travel to the target would increase at a distance but at 100 yards, the only thing you might see is mist from a super sonic round tearing through the air and disrupting the rain drop.

These statistics would be cut in half at 200 yards etc.

[T_PRO_Z]

Thanks for the answers guys. But I'm kinda having a hard time grasping all these formulas since rain is an uncontrollable variable

I am not being bitter in this reply, but unless it was raining in a completely straight line within the diameter of the bullet then you shouldn't have any trouble.

But GOD can do great things, so that may happen!

I do not shoot in the rain because I love my guns and want the best for my guns. I cannot bear to even see one that has been leaning up against a wall fall over 6" into the corner lol.

[kraigwy]

Thanks for the answers guys. But I'm kinda having a hard time grasping all these formulas since rain is an uncontrollable variable.

Its really simple, forget all those formulas and concentrate on fundamentals and not on the rain. Fundamentals (and the bullet) is no deferent in the rain, snow or fair weather.

What will affect you is worrying about the rain and formulas instead of your shooting.