Rain and effects on ballistics today

[Ryo]

OP, did you account for the change in density altitude (environmental changes)? Changes can effect the POI. If you didn't then that possibly explain the POI shift. Depending on your area, some places can change more than others. In OR I was in a class where in the morning one guy couldn't hit crap until I told him the density altitude had shifted. He adjusted his settings in the ballistics calculator and voila, he was back on target.

 

[Graham]

OP, did you account for the change in density altitude (environmental changes)? Changes can effect the POI. If you didn't then that possibly explain the POI shift. Depending on your area, some places can change more than others.

Hmmmm....... It's an environmental change: Either it has; or it hasn't.

Run the numbers: What's the effect of a 5000foot DA change on the trajectory at 100 yards?

In OR I was in a class where in the morning one guy couldn't hit crap until I told him the density altitude had shifted. He adjusted his settings in the ballistics calculator and voila, he was back on target.

Would you be open to considering that his problem, and the result, might have been due to causes other than density altitude, or was he shooting at 700+ yards?

 

[jbailey]

Is there a rule of thumb for telling windspeed from the angle the rain is falling at? For example, rain is at 20* angle from horizonal, indicating some wind, but what mph? I was wondering if there is a similar rule to that of the wind flag rule (I use angle/4 = mph) or the mirage rule? Also, is there one for smoke? I think smoke is similar to mirage. I was actually shooting at a match that feature BOTH rain and smoke - land owner burns his trash and had it burning during match and rain.

 

[George63]

even if the shockwave prevents the bullet from contacting the rain drop the density of the fluid (air) that the bullet is traveling through changes when water in the liquid state ( rain, mist, fog ) is present -

high humidity very slightly decreases the density of air because a water molecule (atomic mass 18 ) claims a similar amount of real estate as an O2 molecule ( atomic mass 32 ) or an N2 molecule ( atomic mass 28 )

liquid water is a whole different story:

liquid water has about 800 times the density of air ( 1000 grams/ liter vs 1.2 grams / liter ) so even a small amount of water in the liquid state will greatly increase the average density of the fluid that the bullet is traveling in - therefor it must slow the travel of the bullet ( the same way the denser air at lower elevation slows the travel of the bullet )

this is really a factor more to be considered for artillery than rifle shooting - as others have said: during periods of precipitation, the difficulty of the shooter focusing on the task and being able to see the target without distortion is likely changing the point of impact more than the difference in air density

as far as some of the explanations given in this thread - the science is weak or wrong - I would encourage the posters to go back to school and take ( or retake ) some science classes - if I can do it at my age so can you - hell, a lot of what I am taught was not even known when I was last in school

 

[_Windrider_]

even if the shockwave prevents the bullet from contacting the rain drop the density of the fluid (air) that the bullet is traveling through changes when water in the liquid state ( rain, mist, fog ) is present -

high humidity very slightly decreases the density of air because a water molecule (atomic mass 18 ) claims a similar amount of real estate as an O2 molecule ( atomic mass 32 ) or an N2 molecule ( atomic mass 28 )

liquid water is a whole different story:

liquid water has about 800 times the density of air ( 1000 grams/ liter vs 1.2 grams / liter ) so even a small amount of water in the liquid state will greatly increase the average density of the fluid that the bullet is traveling in - therefor it must slow the travel of the bullet ( the same way the denser air at lower elevation slows the travel of the bullet )

this is really a factor more to be considered for artillery than rifle shooting - as others have said: during periods of precipitation, the difficulty of the shooter focusing on the task and being able to see the target without distortion is likely changing the point of impact more than the difference in air density

as far as some of the explanations given in this thread - the science is weak or wrong - I would encourage the posters to go back to school and take ( or retake ) some science classes - if I can do it at my age so can you - hell, a lot of what I am taught was not even known when I was last in school

Rain, or the presence of liquid water in the air, does not increase the density of the air. What does increase the density is the atmosphere cooling to the dew point where the air becomes saturated and thus we get rain. So it's the lowering of the temperature that is actually affecting the density. In times of high humidity, the air is actually denser not lower because the temperature/dewpoint spread is less. Remember, density altitude is just pressure altitude adjusted for non-standard temp, humidity no effect on density altitude.

In my experience and schooling, meteorology was my minor in college, I would say that the only time that rain could perhaps have any effect on bullet trajectory is after it has slowed to the point where it is destabilizing. In the early stages where it is actually increasing speed up to its maximum velocity, it has what is known as a laminar flow region around it due to the aerodynamics of the projectile (its what we call the trace). Unless the water is more solid, such as freezing rain, sleet or snow, it would have little effect.

"this is really a factor more to be considered for artillery than rifle shooting - as others have said: during periods of precipitation, the difficulty of the shooter focusing on the task and being able to see the target without distortion is likely changing the point of impact more than the difference in air density"........yes, totally agree.


Posted via Tapatalk HD for iPad

 

[George63]

Rain, or the presence of liquid water in the air, does not increase the density of the air. What does increase the density is the atmosphere cooling to the dew point where the air becomes saturated and thus we get rain. So it's the lowering of the temperature that is actually affecting the density. In times of high humidity, the air is actually denser not lower because the temperature/dewpoint spread is less. Remember, density altitude is just pressure altitude adjusted for non-standard temp, humidity no effect on density altitude.

In my experience and schooling, meteorology was my minor in college, I would say that the only time that rain could perhaps have any effect on bullet trajectory is after it has slowed to the point where it is destabilizing. In the early stages where it is actually increasing speed up to its maximum velocity, it has what is known as a laminar flow region around it due to the aerodynamics of the projectile (its what we call the trace). Unless the water is more solid, such as freezing rain, sleet or snow, it would have little effect.

Posted via Tapatalk HD for iPad

you have a few faulty science issues in this reply:

as stated above - air is 1.2 grams / liter - liquid water is 1000 grams / liter --------- the presence of liquid water ( fog, mist, rain ) suspended in, or falling through the air must absolutely increase the density of the fluid the bullet is traveling through and therefor increase drag/ decrease velocity ---- some of the confusion may be the issue that air by definition is a gas and it is being mixed with liquid water, the density of the gas (air) may not change but the mixture of gas/ liquid will be more dense than the gas itself --- if this is not clear ...........well, as stated above the chem teacher may have a better way to make it clear

in your 2nd paragraph you imply that velocity is increasing outside the barrel .......... uh, no - that is outside the scope of this thread, but there is definitely have some fundamental confusion going on

also remember that frozen water is slightly less dense than liquid water ( why ice floats )

 

[Lowlight]

The higher the humidity ( not talking rain just humidity) the air is less dense than lower humidity. Hence the bullet feels less drag and velocity increases ever so slightly.

That less or more has nothing to do with density altitude as we use it. The idea the air feels heavy in high humidity is a human reaction and not a factor felt by the bullet.

Go to JBM or use any other ballistic calculator, put in 0% humidity and get the dope for 1000 and then increase the humidity to 100%, the dope will be slightly lower.

 

[_Windrider_]

you have a few faulty science issues in this reply:

as stated above - air is 1.2 grams / liter - liquid water is 1000 grams / liter --------- the presence of liquid water ( fog, mist, rain ) suspended in, or falling through the air must absolutely increase the density of the fluid the bullet is traveling through and therefor increase drag/ decrease velocity ---- some of the confusion may be the issue that air by definition is a gas and it is being mixed with liquid water, the density of the gas (air) may not change but the mixture of gas/ liquid will be more dense than the gas itself --- if this is not clear ...........well, as stated above the chem teacher may have a better way to make it clear

in your 2nd paragraph you imply that velocity is increasing outside the barrel .......... uh, no - that is outside the scope of this thread, but there is definitely have some fundamental confusion going on

also remember that frozen water is slightly less dense than liquid water ( why ice floats )

Okay, I am not a ballistician. However, I do know about aerodynamics and when we design, for example, aircraft and their wings humidity isn't something we are concerned about when we discuss the effects of lift and altitude (unless it begins to adhere to the airfoil, then due to induced drag and weight, lift is reduced). When water in the atmosphere freezes or begins to solidify the air does not become less dense. That's because the space that was occupied by that water vapor is replaced by more air. In a vacuum, I would agree with the assumption that the air is less dense with the presence of the rain. But the atmosphere is not a vacuum and neither is the ocean, which is why I agree that's why icebergs float. This is the property of buoyancy, which is way outside of this thread.

My statements on the increase of velocity outside of the barrel is incorrect, I should have said as it slows to the point where the laminar flow begins to break down. Perhaps outside of this thread, but directly related to the density of the air.

We could get really technical and start talking about the saturation vapor pressure of air that is above different materials, but I think it's irrelevant in our applications. If you change humidity values in a ballistic chart and leave everything else constant, you will see minimal change, if any. This is why my personal SOP is just use 50% and split any errors due to humidity in half. Of all the variables, humidity might just be the least important.

Anyway, rain has little to no effect. It's the shooter, and it's the change in temperature that affects the density of the air. Even in a desert where the RH is 10%, if the temp goes down the air becomes more dense.


Posted via Tapatalk HD for iPad

 

[Lowlight]

Air temp and humidity are two separate factors, like your desert reference.

Humidity on its own makes the air less dense, if you have a pressure change with a front coming through, cold air, etc that is separate from the effects of humidity.

Run the numbers, a 175 going 2650 under standard conditions but with 0% humidity will need 11.4 mils. Change just the humidity to 100% and the dope changes to 11.3 at 1000 yards.

 

[_Windrider_]

Air temp and humidity are two separate factors, like your desert reference.

Humidity on its own makes the air less dense, if you have a pressure change with a front coming through, cold air, etc that is separate from the effects of humidity.

Run the numbers, a 175 going 2650 under standard conditions but with 0% humidity will need 11.4 mils. Change just the humidity to 100% and the dope changes to 11.3 at 1000 yards.

I think we are talking about the same thing here. Kind of a cause and effect issue here or chicken and the egg. Temperature is the ultimate variable as it affects pressure, Density and as a side effect, humidity due to chnages in temp and dewpoints.

In its simplest terms, RH is a ratio of temp/dewpoint (alhough much more technical, if you want the real stuff, look up the August-Roche-Magnus approximation, it only gets worse from there). Here is a link to a imple RH calculator, Temperature, Dewpoint, and Relative Humidity Calculator.

When shooting, there are some rules of thumb to help you in your calculations (these i got from Wiki, but have had them in various forms throughtout the years, much like standard temp lapse rate of 2 C per 1000 ft of elevation):

1. For every 1°C difference in the dew point and dry bulb temperatures, the relative humidity decreases by 5%, starting with RH = 100% when the dew point equals the dry bulb temperature

2. a relative humidity of 100% means dew point is the same as air temp. For 90% RH, dew point is 3 degrees Fahrenheit lower than air temp. For every 10 percent lower, dew point drops 3 °F.

If anything, as I cant remember if the Kestrel gives it or not, the above rules will help you calculate your dewpoint when you are only given ambient air temp and the RH. That way you know when its getting closer and closer to the saturation point.

 

[Lowlight]

Who cares...

at 1000 yards it's the difference between 0% and 100% is .1 mils... can you hold .1 mils at 1000 yards ? 1/3 of an inch...

Ultimately if you have DA as a number, that is all you need, the one number and you can figure that fast and easy without any math or convoluted BS.

Even a Casio watch can give you Temperature close enough for shooting, to also figure DA if you know your current Altitude.

The tiny little pieces that go into the "atmosphere" is irrelevant to the shooter. A 3 degree change in Temp is having 0 effect on your shot, so why bother.

This is how people over think it and ultimately fail, or best case use it an excuse as to why they missed.

If you look at Density Altitude alone, we only need to worry about a change of 500 to 1000 ft DA and really just 1000 is fine. So anything that moves under 500/1000ft DA on the Kestrel is a waste of the shooter's time.

You can't hold what you are talking about...

 

[_Windrider_]

^^^^^^^^^^^^^Yes, agreed.

I culdnt hold that on my best day at 500 yds. Just talking it out is all. One could almost completely disregard humidity as long as the other environmentals are accurate. Maybe only on the long ranges beyond a 1000 where you are trying to hit a 1"x1" space on a target should you take the time to consider it, but like you said, even then you couldnt hold the correction if you tried, but it could be dialed in if need be.

set it at 50% and leave it, works for me in my applications.

 

[Graham]

Lindy said it best: Practical precision rifle shooting is about discerning what matters... from what doesn't.

 

[M40_A1]

.1 mil at 1000 yards is 3.6".

Anyway, the problem with George63's theory is that he is back to the idea that a bullet actually hits the liquid medium suspended in the air, which had previously been discussed as not being relevant due to shock wave vaporization.

--------- the presence of liquid water ( fog, mist, rain ) suspended in, or falling through the air must absolutely increase the density of the fluid the bullet is traveling through and therefor increase drag/ decrease velocity ----

 

[Bubb]

Did anybody think about heavier atmosphere conditions during rain? Heavier air could caused more drag about 1/2 to 1 mil at 300 yards??? I don't know but seems that could happen?

 

[Graham]

Did anybody think about heavier atmosphere conditions during rain? Heavier air could caused more drag about 1/2 to 1 mil at 300 yards??? I don't know but seems that could happen?

What are 'heavier atmosphere conditions during rain'? There's a reason that clouds don't come crashing down to earth.

 

[j-huskey]

Anybody else pay attention to the fact that when it rains, humidity does not reach 100%??? Anybody pay attention to the fact that dewpoint and relative humidity and spend time out there while the dewpoint arrives and the grass gets wet but no water is falling. Your feet get wet but there is no visible water coming down.... And on those nights with a thermal, you can see the moisture level coming down and get to the ground, and once again, it ain't water coming down. Its damp air, that reasonable proved education has shown is thinner than dry air. And the bullet will fly flatter in it but you need distance to see it. Not at 100 yards.... Smarter people than most of us have already proved it. 90-95 people just don't believe it and don't grasp it, question it, and don't shoot enough to SEE it for themselves. Lowlights posts are 100% correct and 70% of what else is in this topic is uneducated thought. People who know, BTDT, and have the education are ignored. Jered Joplin said once "shut up and shoot." Good advice. Keep records and repeat the events until you can SEE consistent results. Then what the knowing, BTDT, and educated peoples comments are then clear...

 

[_Windrider_]

Anybody else pay attention to the fact that when it rains, humidity does not reach 100%??? Anybody pay attention to the fact that dewpoint and relative humidity and spend time out there while the dewpoint arrives and the grass gets wet but no water is falling. Your feet get wet but there is no visible water coming down.... And on those nights with a thermal, you can see the moisture level coming down and get to the ground, and once again, it ain't water coming down. Its damp air, that reasonable proved education has shown is thinner than dry air. And the bullet will fly flatter in it but you need distance to see it. Not at 100 yards.... Smarter people than most of us have already proved it. 90-95 people just don't believe it and don't grasp it, question it, and don't shoot enough to SEE it for themselves. Lowlights posts are 100% correct and 70% of what else is in this topic is uneducated thought. People who know, BTDT, and have the education are ignored. Jered Joplin said once "shut up and shoot." Good advice. Keep records and repeat the events until you can SEE consistent results. Then what the knowing, BTDT, and educated peoples comments are then clear...

There is a lot more to it than what you say regarding "rain". if it is raining, the RH is 100%. BUT, just because the RH is 100% does not mean you will get rain, but you will get visible moisture of some kind. It also has a lot to do with atospheric stability, barometric pressures, inversion layers, blah blah blah. But why the grass gets dew when it isnt raining has to do with saturation vapor pressure. the air can become saturated at different temperatures above different types of materials. Im not talking like a thousand feet above, but in the very low heights like over a field of grass and why you get very low layers of fog over grassy meadows but its clear blue just a 100 ft above it. Its the same reason why the bridge ices before the road, concrete gives up its heat energy must faster than asphalt and during rain, even without the presence of snow or freezing rain and if its cold enough, ice will form on the bridge while the roads are just wet.

But we have taken this topic way too far and is no longer about the what the OP was trying to talk about. I agree with what Graham said above, "Lindy said it best: Practical precision rifle shooting is about discerning what matters... from what doesn't"

Nothing of what i have said truly matters to the OP's original post. My opinion...it wasnt the rain.

 

[M40_A1]

Hey, I found the forum where this thread should have been posted, since it is about ballistics, not marksmanship- Range Report & Exterior Ballistics
Range Report & Exterior Ballistics

 

[George63]

.1 mil at 1000 yards is 3.6".

Anyway, the problem with George63's theory is that he is back to the idea that a bullet actually hits the liquid medium suspended in the air, which had previously been discussed as not being relevant due to shock wave vaporization.

no, I never gave any feedback one way or the other about the bullet contacting liquid water -

the bullet does contact and push aside all the molecules that make up the air, when the total atmosphere is denser these molecules have more resistance to being pushed aside, resulting in increased drag

this is true regardless of the cause of increased density ( lower elevation or the presence of liquid water in the atmosphere)

if you think the bullet can be unaffected by the rain drops because you feel that it has no direct contact then you should also think that a person in a car is not affected when the car impacts a guard rail, because there was not direct contact

again this is all esoterics, because when enough liquid water is in the air ( rain, fog, mist) low visibility and optical distortion will affect the shooting much more than the increased drag

I only comment on this because the lack of basic scientific knowledge / understanding irks me

 

[Graham]

if you think the bullet can be unaffected by the rain drops because you feel that it has no direct contact then you should also think that a person in a car is not affected when the car impacts a guard rail, because there was not direct contact

Wow: You have a supersonic car?

 

[George63]

you may be reading a bit to much into the analogy

and avoiding the point:

supersonic or subsonic - drag is affected by the density of the fluid that the projectile passes through