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The angle of the dangle is directly proportionate to...

Oh, never mind.

Altitude is only one factor in air density. If air density effects shot cloud behavior (and physics says it should), we’d have to use air density, which depends not only on altitude, but also temperature and humidity, to make real performance comparisons. Calculating air density quickly is a bit complicated, and the units in which air density would be expressed might make it difficult for a person to attach significance to it. It might be a little more handy to use density altitude. Density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the air density at the place of observation. There are quickie formulas to determine approximate density altitude, which we aviators use to estimate aircraft performance during the planning of a flight.

First, you need to find Pressure Altitude for your given point of observation. Get a local barometer reading in inches of mercury (inHg). Call a small airport for that, or measure it yourself. Subtract it from 29.92 (std sea level baro pressure). Multiply that sum by 1000. (Atmospheric pressure is reduced by approximately one inch of mercury for every 1000 feet increase in altitude. That’s a pretty good approximation for altitudes up to about 10,000 feet. That's called "the standard pressure lapse rate".) Then add that product to the true altitude of the point of observation:

Pressure Altitude = altitude at point of observation + 1000 x (29.92 - local barometric pressure)

Then, to estimate Density Altitude:

Density Altitude = Pressure Altitude + [120 x (OAT - ISA Temp)]

There are a few little definitions to account for in this simple calculation: The Temps are in degrees C. ISA stands for the International Standard Atmosphere, a standard of temperatures and pressures as functions of altitude that closely match those of the real world on a situation selected as a standard -- the "Standard Day". The standard atmosphere was set up to give a reference for aeronautical performance concerns. ISA Temp in the above formula is for the altitude of the point of observation mentioned above. ISA Temp at zero altitude (Mean Sea Level, abbreviated to MSL) is 15 degrees C (59 Degrees F). For every thousand feet above MSL, the temperature profile of the Int’l Std Atmosphere goes down by very close to 2 degrees C. That temperature "lapse rate" is a good approximation all the way up to about 36,000 feet above MSL, an altitude at which you are unlikely to be shooting, I’d wager. OAT is the Outside Air Temperature – i.e. the temperature at the above-mentioned point of interest. The constant 120 makes the approximation work, and I won’t bother to go into its derivation. OK? (Thank goodness!)

So let’s try a sample calculation. Let’s say we’re in sunny Minneapolis MN in July. Elevation (true altitude) is 1000 feet, and it’s 95 degrees out, and the barometer says 29.42. That’s realistic. It happens all the time. It’s likely quite humid also, but we’re going to ignore that for the moment as it is a secondary (though deleterious) effect on air density. Its effect is somewhat compensated by the above approximate formula, by the way.

29.92 – 29.42 = 0.5

0.5 x 1000 ft. = 500 ft.

Pressure Altitude = 1000 ft. + 500 ft. = 1500 ft.

Since the altitude of observation is 1000 feet above MSL, the ISA std. temp for that altitude is 15 Deg C minus 2 Deg C or 13 Degrees C. Local temp is 95 degrees F, which is 35 Degrees C. so . . .

Density Altitude = 1500 ft + (120 x (35 – 13) ft = 4140 ft.

If the temp was 104 F and the baro was 28.92 (not atypical at all), density altitude would be about 5240 ft. – like Denver!

If, in the winter, it was 32 degrees F (zero degrees C) and the baro was 30.92, the density altitude would be minus 1560 ft! That's below sea level.

So in a year of typical shooting, we in Minneapolis might experience a density altitude span of around 7000 ft -- without so much as one step toward the oceans or the mountains! Try not to let the 6 or so inches of stuff between your ears get wrapped around the density altitude while you’re trying to crush those trap shots from the 27 yard line . . . .

Cheers!
Tony

P.S. Where is that patterning guy? Campbell, I think his name is. Let's put him to work on this!

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

My 2 cents......please don't take offense.......

No one is missing birds or killing birds because of altitude, UNLESS you are looking for excuses.

Temperature and humidity have very little effect on patterns. We learned this a long time ago from E.D. Lowry.

I am sure that if you were shooting at sea level one day and then at 10,000 ft the next, there might be a difference, but how many folks shoot at those extremes?

Get out of your heads, it's a bad place to be.

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

Cabin fever must be setting in!!

I'm with you, Mark. I posted what I did so people can have some perspective on the range of air densities and altitudes in which they are likely to have been shooting, so they can give some thought to the likely effects relative to their experience. As of now, I don't think air density has been a big factor in percentages for the clay target games or in hunting, but I am not against some data that shows it is, and what, if anything, I might do about it.

Shooting is like golf -- lots of theories on how things work, endless speculation, mostly on things far, far less important than the fundamentals of technique, and most of which comes from those unable to quantify the effects, equipment manufacturers quick to emphasize equipment over technique so they can sell new stuff, and we users of the equipment, conditioned by our modern times to be quick to grasp at instant solutions to perceived problems.

I hope none of you feel insulted with this next statement, as that isn't the intent, but be truthful with yourself on quantifying or even discerning the effects of some of the things done on the basis of all the speculations and theories you hear.

I'm definitely not against theories. Humanity would be nowhere without the emergence of theories to explain how the world works. The scientific method is to develop a theory based on observations or ideas, and then do the utmost in experimentation to disprove the theory. If the theory holds up to the experiments designed to defeat it, then we are closer to modeling the way the world actually works. After extensive experimentation, we might then, for the time being, be so bold as to call our as yet un-disproven theories laws! Newton did, and his laws still stand up quite well. But the pressure to disprove theories in order to gain deeper understanding of the world is never over. Einstein and many others took things a little further than Newton probably imagined. Their discoveries did not invalidate Newton's theories in all circumstances, and for most practical things in life, we can go by Newtonian physics, but Newton's ideas were unable to explain some other things.

I don't know exactly how much effect air density has on pattern spread, but from my experience and education in physics and mechanical engineering it seems reasonable to think it does have an effect. I can't say my shooting experience has revealed anything definite on that effect, but I'm just one guy, and maybe I haven't been looking closely enough. I would welcome any experimental data to support the theory and quantify the effect. Then maybe we could move closer to "the truth" and see what if anything could be done to give best chances for shooting success. For now, you could say though I'm not a "doubter", I'm just one of those guys with my head in the sand, working on making good shooting moves. Very Happy

Joined: 09 Mar 2016 Posts: 753 Location: Mn.

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

So now I will ask.......with the exception of Wyochukar, who on this forum hunts at both 900' and 7,300' of altitude?

OK so how many of us have to even think about this?

Guest

Joined: 09 Mar 2016 Posts: 753 Location: Mn.

FourTrax lives at 700 ft. elevation and is spending 5 weeks at ~5,000 ft. he is there right now. With surrounding elevation of +9k feet. Another member on here is showing him the ropes in that area. Waiting on a report from him to see if it something I want to start doing next year during the coldest parts of winter. Although I am not much of a quail hunter. But beats shoveling snow.

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

I never run for cover. EVER.

I am also not one that changes chokes at the drop of a hat.

My point/question is......how many people actually have to take this into consideration?

There is only one person on the 16 ga. Society, that I know of, that hunts at varying elevations where a choke change might be in order.

There is no question that there is a difference in patterns, but the differences in elevation need to be relatively large in order to start changing chokes.

Guest

Can I hide behind you? Very Happy

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

go right ahead, not promising anything!! Mr. Green

Joined: 09 Mar 2016 Posts: 753 Location: Mn.

I have , but not like you guy's .

Dumb Ole hillbilly had better watch what they talk about , whew can't say a word in passing conversation for nothing.

Guess I shouldn't say this , but I just got 2 cases of Fiocchi hulls from Mike Graf , loading 5/8 oz of #9's we shall see if a hundred straight is in the future with all those hulls.

Regards Nick