Barometric pressures at altitude

Some measured values people might find useful for setting up drop tables. These are just from a barometer app on my phone.

For my 7mm08 the drop at 300m is about 3cm less and the wind drift for 5m/s full crosswind is 6cm less at 1500mthan at sea level.

I make up my chart for 500mASL and include a note with the correction for 300m at 1500m.


Waihohonu hut
Alt 1150m
Temp 10.5C
Baro 888hPa
Wind 2m/s

Rangipo hut
Alt 1550m ASL
Temp 8.8C
Baro 841hPa
Wind 4 m/s

Mangaehuehu hut
Alt 1280m ASL
Temp 12.8C
Baro 873 hPa
Wind 2.5 m/s

If someone could post measured pressures at 2000m and 2500m or a link to an online reference table that would be interesting,thanks.

https://keisan.casio.com/exec/system/1224579725

Altitude alone can be a very inaccurate indicator of air pressure

Relative air pressure is what you need to focus on, measure it with a device that doesn’t convert altitude into air pressure readings

PS: Most hunters can use an average of 28inhg and harvest a lot of deer

Attachment 152063

Thanks @Puffin that calculator agrees with all three of my measurements closer than 5 hPa.

Whats the device youve got in that pic Saum ?

Im pretty sure phones will be measuring station pressure ie actual pressure on site not calculating from GPS altitude. The appis supposed to be used to track trend over time too (although ive never been patient enough to get a good trace of it).

It’s a Skywatcher Explorer 4
Relative Baro , temp, air speed etc, metric and imperial readings

Ok you've made me ask. Whats “relative air pressure” ? Is it density altitude, percent of sea level etc ? Where do you put it in a ballistic calculator ?

Station pressure is the awnser ,
What was the question?
This is why I love the kestrel as it's all done for you.
My samsung phone has station pressure sensor but no thermometer.
You can just guess that

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Quote:

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Originally Posted by andyanimal31

Station pressure is the awnser ,
What was the question?
This is why I love the kestrel as it's all done for you.
My samsung phone has station pressure sensor but no thermometer.
You can just guess that

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This is on the samsunghttps://uploads.tapatalk-cdn.com/202...9619f773a0.jpg

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There are a bunch of ways to skin this cat depending on your app and skill set

Probably the easiest way is to measure your absolute air pressure with a barometer and enter that into your app. Often the app will then set the altitude to zero as alt is irrelevant after knowing the absolute air pressure

Absolute air pressure is the measured air pressure right where your standing, the reading taken with an actual hand held barometer.

Air pressure can change three times in an hour quite easily, without you even moving an inch

At the end of the day use what works for you

Andyanimal has extensive experience and has a system that’s reliable

Ultimately it is air density is what affects bullet drag.
This article is one of the best I have read that simply explains what happens and what inputs were needed.
Absolute air pressure is station pressure.

https://bisonballistics.com/articles...cs-calculators

A phone with an in built barometer measures station pressure nothing else.
With temperature and relative humidity values, density altitude can then be calculated.

Watches with barometer in them are getting cheap... Used one for years, also gives you a back up compass depending on the model

Use my watch for air pres(station pres) guess temp within 10 deg is close enough(but most people can guess within 5deg.) if you have correct air pres. and set humidity to 50%.

Quote:

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Originally Posted by blair993

Use my watch for air pres(station pres) guess temp within 10 deg is close enough(but most people can guess within 5deg.) if you have correct air pres. and set humidity to 50%.

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Yep I agree that using your phone or watch for station pressure and guessing temp and 50% humidity is exactly what i would be doing if i didnt have the kestrel.
For $400 you can get the kestrel 2700 which has every thing you need for getting an accurate elevation and wind solution out to 875yds as has the compass and applied ballistics that you can purchase custom drag curves.
The only other good option i have used predominantly in the past is the 2500 kestrel and put that into your phone app manually which essentially gives you the same info except it's a lot slower than the 5700 and 2700.
If you really want to do your head in start looking at spin drift, aerodynamic jump and coriolis!

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If you really want to do your head in start looking at spin drift, aerodynamic jump and coriolis!
Why bother? Its hunting distances. If you miss due to aero jump or coriolis you need to think of better excuses.

Quote:

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Originally Posted by blair993

If you really want to do your head in start looking at spin drift, aerodynamic jump and coriolis!
Why bother? Its hunting distances. If you miss due to aero jump or coriolis you need to think of better excuses.

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Yep your dead right there!
It's the rabbit hole you have to watch that you can fall in once you've mastered your predetermined hunting distance and get the bug for really stretching things out.
I have the tshirt.

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I'v stretched things. still didnt use aero jump or coriolis

Quote:

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Originally Posted by blair993

I'v stretched things. still didnt use aero jump or coriolis

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The 5700 gives it to you for free.
At 2.2kyou need eveything you can get.

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Ok. I didnt use it at 2k and worked out ok. other apps/solutions also do it. Doesn't mean you need it.

Quote:

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Originally Posted by blair993

Ok. I didnt use it at 2k and worked out ok. other apps/solutions also do it. Doesn't mean you need it.

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Spin drift yes you can turn it of as your wind call is more important than spin drift but as AJ effects elevation that should be used in your calculations.
As for coriolis I havnt got the brain power to work that out with out my kestrel.
It's very simple for the kestrel as it has the latitude put in and the compass with DOF input.
I like using all the fruit as then I am familiar with it when I need it.
Different strokes I reckon

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Hi here are the air pressure over the range of altitudes we are likely to shoot in NZ.
These are from the Casio Web Calculator which Puffin kindly showed in his post.
I've set the sea level pressure to 1013 hPA (it can vary from about 980 to 1030 depending on the weather system on the day).
I've set the temp to 10C but of course this generally falls about 10C per 1000m and you can put this into the calculator and see if it makes a difference for you.

Attachment 152423

I think next time I do this I'll note what the sea level pressure was at the time.
However, it looks as if the web calculator gives close enough values for my purpose, which is making up a drop table so I don't have to refer to a barometer for each shot. Undoubtedly, the best way to get an accurate adjustment for a shot longer than 500m is to measure the pressure where you're shooting and put that into a ballistic calculator at the time.

I'm finding my kestrel most useful for the simple fact it holds all my mates calibres and setups and i can flick between them very quickly. It gives you something constructive to do when ranging and glassing.
Also reminds you what the temp actually is which you can lose track of if you've been moving about.

Things i hate about phones: they can be your lifeline so you feel reluctant to be playing around with AB till it flattens your battery. Also the screen backlight, half the time the thing is set too light for mid day viewing in the field. cant use it with gloves.

but back on air density. I used to be madly into tracking DA when i was into field target air rifles. I used to use dew point, actual elevation, temperature and baro. There an old App for phones you just put that in and it works out DA

Here are drop tables I made up for my 7mm08 for altitudes 100m up to 2000m ASL.
They're from Strelok Pro using the pressures in the chart above, holding temp at 10C.
I've colour coded the situations where the predicted adjustment from the 100m ASL value is more than 3 clicks (0.3 mRad or 1 MOA approx). Of course, every click counts specially at longer ranges but for most hunting less than 1 MOA error can be ignored. The ICFRA 5 (bull) ring is 2 MOA across and so is a 12" steel plate at 600 yd so if your MPI is 1 MOA out, your score will suffer a lot even if your grouping is only 2 MOA. I was interested to find that altitude won't require more than 0.5 mRad adjustment for my system, out to 600m and that out to 300m I can use a sea level drop chart without adjusting a single click. If I make a drop chart based on 500m or 1000m ASL that will be pretty close for most situations.

Attachment 152645

Representative altitudes in NZ.


North Island
Kaimai plateau 500m
Clements Rd 700m
Venison Top 1450m
Waipakihi flats 940m
Totara Flats 200m
Mangahuka Hut 1280m

South Island
Cupola Basin 1580m
Rakaia riverbed 800m
Sealey Tarns 1300m
Garden of Eden 2000m
Greenstone flats 500m
Teichelman Ck Tahr ballot site 1450m

Ranges
Whatawhata 30m
Tokoroa 340m
TECT park 500m
Trentham 50m
McLeans Island 50m