Does rain effect bullet flight path.??

[native hunter]

G"day All
Just wondering does the rain effect bullet flight path.?
If the rain was heavy enough could you see it(projectile) travel through the air over a long distance.??
At what range would it effect it more if so.???
I imagine the projectile would hit a few drops of rain over any given distance, would it not.????
Has anyone had any experiences.?????
Regards

[Rinso]

Native,

I am no expert but my observations and opinions are ..

Just wondering does the rain effect bullet flight path.?

Rain effects bullet flight but not in the way you would think. The rain itself does little however the thicker atmosphere has a marked effect as does cooler air over longer distances.

If the rain was heavy enough could you see it(projectile) travel through the air over a long distance.??

You can see the pressure wave that the bullet creates as a V shape as it forces the air and water away.

At what range would it effect it more if so.???

like all things ballistic the effects are from start to end of bullet flight. The longer the bullet flies the more the effect.

I imagine the projectile would hit a few drops of rain over any given distance, would it not.????

The bullet is actually pushing a force cone of air, this combined with the size of the bullet would make actual rain drop strikes minimal if at all.

Has anyone had any experiences.?????

Had a shot drop half a target at 500M after a sudden drop in temperature and sleet falling.

This may be all wrong but I am sure I will be corrected.

cheers
Rinso

[Mick]

Fluid dynamics explains something called detached shock, which would most likely stop rain from contacting the bullet while it was supersonic. It is a pressure wave that forms just ahead of a supersonic body and curves around it. That is also what causes the bullet trail you can see if you are watching down a spotting scope.

But in general, the more dense air because of humidity would most definitely have a noticeable effect on the drop of the bullet.

[zzsstt]

I agree that denser air (due to temperature or humidity) will affect the bullet. Basically it is (obviously) all down to energy. The bullet starts out with an amount of energy (kinetic energy) that depends on its mass and velocity. As it moves it must transfer some of that energy to whatever it has to push it's way through (air, rabbit etc.). As it's mass is constant it's velocity must decrease to "supply" the energy that is transferred to whatever has to be pushed out of the way.

Now gravity is constant, and therefore the vertical acceleration of a bullet (or anything else) is constant. If you drop a bullet at exactly the same time as firing one (horizontally) from a rifle, they will both hit the ground at exactly the same time*. And they will both drop by 3" (or any other measurement) in the same time. What this means is quite simply that the longer a bullet is in the air, the greater will be it's vertical speed and the further it will have dropped. So anything that slows down the horizontal speed of the bullet will cause it to take longer to reach a target at a given distance, and therefore it will have dropped further by the time it gets there.

The detached shock theory may stop a rain drop from contacting the bullet, by the bullet is still providing the energy to move the water out of its way, so it is still slowing more than it would in air of the same humidity and temperature (ie density) but without the liquid water droplets that have to be moved.

Therefore the denser air (higher humidity, lower temperature) will slow te bullet and increase its drop, but additionally how much liquid water has to be moved out of the way (i.e. how heavy the rain is) will also make a difference. The ultimate extension to this is the fact that if a bullet is fired in to water (perpendicular so as to penetrate not skip off) it doesn't go very far, as it very quickly expends its limited amount of energy moving water out of the way!

*Actually if you drop a house brick at the same time as firing the bullet, they will also hit the ground at exactly the same time, as will anything else that is not affected by too much air resistance.

[Ned Kelly]

G'Day all,
please remember that water vapour (humidity) weighs about 5/8ths that of 100% dry air all else being equal.

So high humidity days also means the atmosphere the bullet must pass through weighs less and it wont slow down as much as it would in 100% dry air.

All in all it would come down to the actual weight of air needed to be displaced by the bullet inside the barrel. This can have an effect on the harmonics since the time the bullet spends in the barrel will change due to the air pressure in front of it; higher atmospheric pressure, means more air/water vapour molecules (and weight) to push, a longer barrel time for the bullet and accuracy could change as a consequence. Some shooters in the US are looking at temperature corrected air pressure (density altitude) to see if there is a correlation to tuner settings in BR rifles FWIW.

As for the rain having an effect on the bullet in flight, I do believe if you hit a droplet you will lose a shot as I've had unexplained flyers in heavy rain in BR matches and no it wasn't a droplet inside the muzzle (Portland, Victoria has a fully covered firing line out to 4m in front of the barrel) which definately will throw a shot.

Cheerio Ned

[Mick]

G'Day all,
please remember that water vapour (humidity) weighs about 5/8ths that of 100% dry air all else being equal.

So high humidity days also means the atmosphere the bullet must pass through weighs less and it wont slow down as much as it would in 100% dry air.

Weight isn't a concern. The friction it provides is the determining factor, and humid air is more dense than dry air, so creates more friction.

[Ned Kelly]

G'Day Mick,
Weight is a concern, ole Mr Newton said about equal and opposite forces, well that bullet must push that air out of that barrel and if it weighs more it will be slower. You may be referring to humid air flow being stickier, but at these speeds the air flow is supersonic inside the barrel and the heat from compression immense. Supersonic air flow uses different rules to subsonic flow. And the relative stickiness of humid air is fairly irrelevant to a bullet doing 3000fps me thinks!

Actually, the speed of sound is relative to the air temperature so the speed of the exiting air from inside the barrel may be 3000fps, but due to the temperature from compression, may still be subsonic.......any ballisticians out there want to wade in?

I've checked my old aircraft mechanic text books, water vapour weighs, as i said earlier 5/8th that of dry air, as the water vapour displaces dry air, for ANY given volume, the air then must weigh less than a 100% dry day, for the same air pressure and temperature.

You will find humidity (amount of water vapour) is expressed as a percentage of what the air can hold for a given temp. Higher temp, a greater amount of water vapour can be held before it reaches 100% saturation compared to a cooler day. A 100% humid day at 15degC will hold less water vapour than a 35degC day with 100% humidity

But water vapour is always 5/8ths the weight of dry air, or put another way, a water molecule is 5/8th 's the weight of an oxygen molecule.

The bullet must push the weight of the column of air (and water vapour) that is in front of the bullet out of the barrel and if it is heavier weight or higher air pressure that when the load was developed, the bullet must do more work (lose energy) and stay in the barrel longer which affects the harmonic vibrations of the barrel.

A good load is one that is not affected by temperature variations and as a consequence varying humidity.

cheerio Ned

[Mick]

Supersonic air flow uses different rules to subsonic flow. And the relative stickiness of humid air is fairly irrelevant to a bullet doing 3000fps me thinks!

Basic laws of physics, motion and thermodynamics would disagree.
The bullet has to cut a path through the air, no matter what speed it travels at. More dense air requires more energy be expended to cut that path. Yes, relative humidity varies with temperature, so the amount of energy will vary if the relative humidity is 90% on a 10 degree day to that of a 30 degree day.

Maybe the term humidity is a bad one to use, I guess saturation is probably a more correct term for what I'm talking about.

[zzsstt]

Woohoo chemistry!!

Water = H20 ( that's 2 H's plus and O)

The molar mass of Oxygen (O2) is 32, hydrogen (H2) is 2

So the molar mass of water H2O is 18, whilst O2 is 32

But "air" consists of many things, O2, CO2, N, He etc. etc. The molar mass of "air" (given the normally accepted composition of "air") works out to be about 29. So indeed, the more water vapour in the air the lower it's density.

However, at 50% relative humidity, 25C, there is only about 10grams of water vapour per kg of air, which is 1%, and at 100% RH the figure rises to 20grams (2%). So the actual difference made to the mass of air with changing relative humidity, now that I bother to calculate it, is (for a change of RH from 50% to 100%) 1 - 18/32 of 1%. About 0.4%, or "bugger all", as it's known technically.

Realistically the change in density of air due to change in temperature or altiitude is probably far more than this, with , for example, a temperature increase from 20C to 30C causing a 3% reduction in air density.

[Model70]

I am no expert on the matter but whilst at silverdale it started pissing down and I noticed you could, I guess 'hear' the bullet or the path it was taking. Im gueassing its the pressurised air forward of the bullet pushing its way through??
As a matter of interest, as for seeing the bullet, at St Marys indoor range in the right light you can actually see the projectile travelling forth, or atleast the reflective light off the copper jacket.
I only noticed it in the heavier .303 and the mongrel 7.62x54r Nagant carbine (i hate that gun!!)

[DC]

at St Marys indoor range in the right light you can actually see the projectile travelling forth, or atleast the reflective light off the copper jacket.

Yea while scoring at my range ive seen the sun reflecting off the ass of the projectile a few times... very cool

[Mick]

Woohoo chemistry!!

Water = H20 ( that's 2 H's plus and O)

The molar mass of Oxygen (O2) is 32, hydrogen (H2) is 2

So the molar mass of water H2O is 18, whilst O2 is 32

But "air" consists of many things, O2, CO2, N, He etc. etc. The molar mass of "air" (given the normally accepted composition of "air") works out to be about 29. So indeed, the more water vapour in the air the lower it's density.

However, at 50% relative humidity, 25C, there is only about 10grams of water vapour per kg of air, which is 1%, and at 100% RH the figure rises to 20grams (2%). So the actual difference made to the mass of air with changing relative humidity, now that I bother to calculate it, is (for a change of RH from 50% to 100%) 1 - 18/32 of 1%. About 0.4%, or "bugger all", as it's known technically.

Which is why in my last post I changed the term I used. Humidity is really the incorrect term for the point I was trying to convey. Saturation, ie. condensing or condensed water in the air, is more relative to the question being asked.

Realistically the change in density of air due to change in temperature or altiitude is probably far more than this, with , for example, a temperature increase from 20C to 30C causing a 3% reduction in air density.

Indeed it does. Fairly common knowledge that loads may have to be varied with decent altitude or temperature changes.

[Ned Kelly]

G'Day All,
from what I've read about the US army sniper training, they do not worry about humidity; only altitude, air pressure and temperature as these are the three main variables that have a direct effect on the bullets flight. The temperature part of the equation relates directly to the amount of water vapour (level of saturation if you like) in the air, so by allowing for temperature you have automatically allowed for the humidity.

Cheerio Ned

[DC]

hey ned,

Alot of the stuff here is a bit far out for me but I do know that the list of things you need to account for when taking a shot gets bigger, the longer the shot is.. I dont know if the snipers you are refering to are using a M40 or a "M107 .50BMG" but I saw the record for.... longest successful target shot with the M107 being around either 2500yards or 2500meters (I forget which)

And At that range the List variables worth accounting for includes the rotation of the earth! along with elevation(in relation to target), barometric preasure, humidity, projectile spin drift or "The Magnus Effect", temperature aswell as all the other trajectory thingamajigs we hold so dear

[DC]

The more i thought about it the more i couldnt think where i heard it haha (old age)
I think this is the shot i heard about........

"The longest range recorded for sniper kill is 2,430 metres (2,657 yd), accomplished by a sniper from Newfoundland, Corporal Rob Furlong, during the invasion of Afghanistan, serving the Canadian Forces, using a .50 caliber BMG (12.7 mm) McMillan TAC-50 bolt-action rifle. This meant that the bullet had a flight time of ≈ 4.5 seconds, and a drop of ≈ 70 meters (230 ft)."

haha got the Cal right.. at least i know i didnt dream it now