Hi,

I'm hoping someone can clear this up for me.

If 2 identical projectiles are launched at identical speeds in the same air temperature and elevation above sea level.

Which projectile will have the flatest trajectory.

The first projectile travels through humid air.

The second projectile travels through dry air.

Has anyone done any testing as opposed to theory on this.

My testing favours the dry air with the flatest trajectory, am I correct or is there some other factor at work.

Thanks for any help

Yeah, you are tracking. Try Bryan Litz's book Applied Ballistics for Long Range Shooting. It's a good read.

quote:

Originally posted by x-rings:

If 2 identical projectiles are launched at identical speeds in the same air temperature and elevation above sea level.

Which projectile will have the flatest trajectory?

My testing favours the dry air with the flatest trajectory, am I correct or is there some other factor at work.

Thanks for any help

x-rings,

I've not done that particular testing, but applaud your efforts and would like to see your data.

Think what your really trying to test are changes in air density and bullet drag with changes in humidity.

As you noted, air temperature and altitude would have to the same to get at the effect of humidity. But barometric pressure would also have to be constant! Since weather changes in humidity also come with barometric pressure changes (and wind changes that can effect trajectory) - This could be a problem trying to get shooting days with different humidity at the same barometric pressure and wind.

I don't know anything about how humidity would effect bullet drag, but if you'll google "humidity chart" you should find one that shows the air density. Air density is effected by the following in decreasing order:

1) Barometric pressure
2) Temperature
3) Altitude
4) Hunidity

PS: Don't ignor effect of wind on trajectory and barrel condition on muzzle velocity.

Humid air is less dense, but I can tell you I have never measured much of a difference.

Temperature has the largest affect on trajectory. Even in AZ I have to take an MOA off between winter and summer conditions at 700 yards.

If you want to minimize the effects, shoot the highest BC bullet you can find. That is why I love heavy bullets in my .220 Swift.

AZ wouldn't the humidity in the air cause drag on a bullet. I know you live in one of the driest places in the US does your guns shoot diffrent when you go to a humidt place to hunt or around large bodies of water? Just a question.

Humid air is less dense than dry air, but like I said, I have never noticed much of a difference. For that matter, I haven't noticed a big diff with barometric pressure, unless the altitude is high. I do notice a difference winter to summer.

Humidity is a really tricky one to isolate as a trajectory parameter.
- humidity is normally stated as relative humidity in weather reports.
ie
its the percentage humidity relative to saturated air at the particular temp.
- the absolute amount of water that saturates air is directly proportional to the air temp.
ie
the same humidity at 2 different temps has a significant difference in the amount of water absorbed in the air.
ie ie
the same amount of water absorbed in the air has lower relative humidity at the higher temp.

So when you are talking humidity you really need to be talking the % moisture in the air rather than relative humidity to have moisture as a parameter that is temp independent.

otherwise you have a situation where the relationship you develop for moisture content as relative humidity at one temp is a different scale of effect at another temp.

High relative humidity is most often encountered in a low pressure environment .........not withstanding local effects of proximity to major water bodies.
In that context AZ is correct about relative density, both at constant temp and in the conditions you typically find it in the field.

Regretfully XR you backed the wrong horse .
The trajectory is flatter with higher water vapour in the air.........with other parameters held equal.
your contrary observations are probably explained by not referencing air pressure as a constant..........given that air density is higher at higher pressure and influences velocity reduction & therefore bullet drop the most.

The physical theory identifies the parameters that need to be held constant to effectively answer your proposition about flattest trajectory in either a theoretical discussion or practical examination.

'93..............
unfortunately water vapour ( as humidity, as unsaturated air) is lighter than both Oxygen & nitrogen molecules ........which between them make up the vast majority of the air content.

As AZ identifies humid air is less dense than dry air.
This is not an intuitive concept when you think of H2O as a water molecule rather than as a vapour.

when we get to the extreme end of humidity where we have moisture suspended as a light mist the density of the air does increase and dry air will produce a flatter trajectory.

Ohh what a tangled web such a simple question can lead to.

Bottom line is..........its damned difficult to find in the natural environment the natural conditions with the necessary constant parameters to physically & adequately test the question asked.......within a timeline that the internal ballistics associated with the test can be guaranteed to be constant too.

He He........its almost a lifetime project.

a good ballistics program can answer the question theoretically PROVIDED the program is actually converting relative humidity at temp & pressure to actual % water vapour content & its influence on the air/water vapour mix density in its ballistic calculations.
That is something you will only know if you interrogate the appropriate program algorithm deep inside its programming.

the simple approach is that temperature at other constant parameters trends exactly the same direction ( but to a different extent ) as actual humidity as a vapour% does.
So the effect of temp change on trajectory will have the same trend as change in humidity.

Its much easier to find the conditions in the natural environment where the other parameters are constant but with varying temp.
remembering that the actual water vapour % will be relatively constant in still conditions while the relative humidity will change with temp, otherwise in those same conditions . a much easier proposition to test in a practical sense on a given day.........IF you accept the base line physics that air density trends the same way for temperature as for humidity (expressed as % moisture vapour content ) as single variable parameters in its affect on projectile trajectory.

Designing tests to adequately isolate them to the influence of a single parameter is typically a lot harder than executing the tests in an inadequate manner that leads you up the garden path with a myth that you will swear is true , because you did the test ( but unintentionally inadequately). Many are the scientists that have created myths in good faith ...........let alone laymen.

darn good question , but not one I would attempt to devote time to answering in practical results.......just too hard to find the right conditions to answer the question validly with actual results.

My 2 cents thats worth 2 cents only, I know for a fact that winter air( cold) has a profound effect on the lift that an aircraft wing can produce. If i remember correct its almost 1/4 more potential lift. Drier tighter packed air=more lift. Summer evening air thats heavy with moisture causes much drag and much less lift. 2 cents worth .

This is not so difficult to explain. I live in Houston so I am something of an expert in this area.

High temps and corresponding high humidity tend to make bullets feel very sluggish. They simply don't have the energy to perform as well as they can in nice brisk dry air. This effect is most pronounced in the bigger bores. Their large mass makes them heat bombs, unable to shed internal temps as efficiently as their smaller kin.

We have unacceptable rates of bullets falling out of the air from heat exhaustion. Saturday and Sunday mornings are the worst with the morning after Lady's night following a close second. This can be minimized or avoided altogether with a little discipline the night before but you know, bullets will be bullets.

Anyway, I hope this helps.

Tiggertate: That is funny!

The only time I saw climate conditions making a difference on ballistics worth noting was when going to/from extremes. For example: Going from Fort Bragg, NC or Panama to La Paz, Bolivia (13,000' altitude). If you find minute differences note worthy, everything affects ballistics and accuracy differently everytime you pull the trigger.

The best data you can have is your own. Use all of the "instant sniper" information out there as a very basic guide (or amusement). You want to know what you, your gun and loads can do? Keep a detailed log everytime you shoot. You should eventually see patterns and will have educated knowledge of what you, your gun and load will do under similar conditions based on trigger time experience.

I like that verbage..."instant sniper"... like so much in our culture right now, everything is instant and disposable.

"Density and humidity, how they affect BC"

Well, as explained above humidity affects density slightly, but neither of these affect BC. At colder temperatures humidity is less of a factor because the vapor pressure of water is much less. So at low temperature 0% vs. 100% relative humidity is really about the same thing. But at high temperatures, say like 100 degrees, 100% humidity would be straight water vapor which is about half as dense as air.

Speaking of weather forecasts, it seems like all of the pressures they report are not absolute, but corrected for sea level. So then you need to think about altitude, which is usually a much bigger difference than humidity anyway.

quote:

Originally posted by SFRanger7GP:
The best data you can have is your own. Use all of the "instant sniper" information out there as a very basic guide (or amusement). You want to know what you, your gun and loads can do? Keep a detailed log everytime you shoot. You should eventually see patterns and will have educated knowledge of what you, your gun and load will do under similar conditions based on trigger time experience.

I keep a log and enter data into it every time single bullet that I shoot. I shoot at either gongs up to 500 yards or painted rocks. Both provide feedback after each shot.

In any case, the practical effects of RH on bullet drop can be just about ignored.