Kestrel Altitude Reference Zero? Location change from PA to CO

[Drewdemon]

I live just outside the Philadelphia area and do 99.9% of my practicing surrounding the city. I bought a Kestrel (AB) but also use JBM ballistics to create manual charts. I used my charts to confirm/trust the Kestrel and it didn't let me down...until recently. My dad and I had planned a hunting trip to Colorado that was five years in the making. I had planned to use the kestrel as my primary ballistic method then use manual JBM ballistic charts as a backup. To create my JBM charts i used pressure, altitude, etc, that i found online for our hunting location one week in advance.

Once we arrived at our cabin i pulled out my kestrel and the pressure readings were way outside (low) of any weather/airport/etc readings i had checked online beforehand. I spent the 1st few days of the hunt scratching my head and playing with Kestrel settings. In the pic 27.82 was what I expected but had to change the reference altitude to our location to get that number. Pressure at 22.56 was with altitude reference set at zero and what i though was the correct setting. In the end I drove to a place where i could fire off a few practice rounds and confirmed my charts were good (Kestrel not good). Im only about a year into precision rifle shooting but what am i doing wrong with my Kestrel? I doubt i'll travel to Colorado anytime soon but would really like to kow just in case.

Thanks

 

[Nik H]

I used to go to Crested Butte a lot and the pressure your Kestrel is providing is close to what I would expect for the altitude shown by the Kestrel. You can check for yourself at

http://keisan.casio.com/exec/system/1224575267

 

[Sogan]

I'm pretty sure that the Kestrel in AB mode uses the correct baro, pressure and alt reference settings regardless of what you set them to in the main settings. It does this to guarantee it gets the correct measurement without people accidently messing up the AB settings, or so ive heard.

 

[Drewdemon]

The altitude in our area was more like 5,600-6k but the expected BP was considerably lower. If I had used the kestrel I would have missed my buck. Maybe I'll try contacting kestrel

 

[timintx]

Drew ,Have you calibrated your Baro on the Kestrel? The altitude will not be correct all of the time because it is referenced off of your baro. To calibrate the Baro you can go to their website and they have instructions on how to do so.My kestrel was way off when I got it new so I went to the local school and they have a noaa weather station there and I pulled it up the baro on my phone and then set the kestrel. It has been on every since Good luck to you.

 

[Drewdemon]

Thanks, I will try that...

 

[ZiaHunter]

Drew:

I believe the Kestrel AB at least the 4500 uses station pressure in its calculations regardless of what the barometer reading is on the screen. The airport pressures listed for any particular area are generally shown adjusted for sea level and not station pressure. Did you use station or barometric pressure when preparing you charts? General recommendation is not to adjust the elevation on the BP screen so the unit will always show station pressure and when inputting atmospherics into JBM use station pressure.

 

[delfuego]

Make sure you select/de-select the correct box in JBM. You would need to uncheck the "Pressure is Corrected" box in JBM. you are inputting the un-corrected pressure from your kestrel. The corrected for altitude pressure for Colorado will be 29.xx, where as the uncorrected pressure (station pressure) with be much lower.

 

[Drewdemon]

ZiaHunter, I used a host of website and apps. The rational was to see differences from one site to the next to verify they matched my kestrel at home (PA). I primarily used the online (not the app) weather underground site. I have the 5700 kestrel.

Delfuego, my charts were created with "pressure altitude" unchecked. Once I found a spot to practice I confirmed my zero then shot out to 450 meters. If I had used the kestrel ballistic info I would not have hit at 450 meters.

Hope that helps

 

[Nik H]

That is totally bizarre. Maybe your Kestrel is not working correctly

My Kestrel 5700 is spot on to 700 yards including CO at 9250 feet.

 

[davsco]

sounds like you're using the density altitude components separately, but my understanding is you can do whatever you want to the kestrel settings and it will always provide an accurate density altitude. if that is incorrect, someone please let me know.

 

[delfuego]

JBM Trajectory doesn't use DA. I would recommend this. It is super easy and gives good data as long as the correct info is entered. I can print a JBM card using just altitude and "STD atmosphere at Altitude" and be good out to around 1k. If I need real time data, I use a kestrel for DA and Shooter App on my phone. If you're coming back out to CO; you can create some verified dope cards and print cards with DA's from 5k to 10k. This should take care of you for most everything here with the exception of chasing Big Horn sheep in the tundra. Honestly you will only start to see a real difference in drop after around 600y.

I see more people struggle with AB/Kestrel than anything else. You can also send your Kestrel in and they will calibrate it, or go to your local airport, they will have a station pressure reading and you can verify it against yours. Also turn that stupid aerodynamic jump thing off. It will give you bad data here in CO.

I would recommend simplicity. Good luck!

 

[DocUSMCRetired]

DA is ok for minute of man, but it can be fooled by different combinations of pressure and temp which makes it unreliable. I can get 2 completely different atmospheric conditions to read the same DA.

The Kestrel Elite uses the physical pressure at your location. Which is what you have. You do not need to adjust anything unless your pressure sensor is slightly off. In which case you can calibrate it. Do not worry about the Altitude on the weather side, unless you are needing it for backpacking or such. Only look at the environmentals under the environment section of the ballistics side.

 

[Drewdemon]

Thanks everyone

 

[colorado_native]

For what it is worth, my Kestrel 5700 consistently puts out the most accurate info of any of the other ballistic programs I have used. I have shot regularly with it in Colorado and New Mexico and then took it to close to sea level with the same rifle in Virginia and it adjusted my charts appropriately.

 

[regency]

DA is ok for minute of man, but it can be fooled by different combinations of pressure and temp which makes it unreliable. I can get 2 completely different atmospheric conditions to read the same DA.

The Kestrel Elite uses the physical pressure at your location. Which is what you have. You do not need to adjust anything unless your pressure sensor is slightly off. In which case you can calibrate it. Do not worry about the Altitude on the weather side, unless you are needing it for backpacking or such. Only look at the environmentals under the environment section of the ballistics side.

I was under the impression that density altitude was the end all, be all for PRS shooting when using a kestrel or plugging an environmental factor into say Ballistic AE or JBM... I'm new to my kestrel, any thing I need to change or do differently when inputting data for the environment?

 

[DocUSMCRetired]

I was under the impression that density altitude was the end all, be all for PRS shooting when using a kestrel or plugging an environmental factor into say Ballistic AE or JBM... I'm new to my kestrel, any thing I need to change or do differently when inputting data for the environment?

DA is less than ideal for precision. It works ok for minute of man and fast calculations. However Temp + Station Pressure is going to be more accurate. Not to mention I can take two completely different combinations of atmospherics to read the same DA. The problem here is that the speed of sound is determined mainly by the temp of the air -40 deg F (1002 fps) to 140 deg F (1200 fps). This changes the point at which the bullet reaches the transonic barrier, and the amount of drag at that time/velocity that the bullet experiences.

This is why in our mobile app, even if you use DA we still require you to input the temperature. So the drag can be correctly calculated for.

For short range shooting you can get away with using DA simply because you won't be encountering the Mach 1.1 - 0.9 zone.

 

[KestrelMeters]

When using a Kestrel with ballistics, now the Kestrel 5700 (though photo shows the 4500) https://kestrelmeters.com/products/kestrel-elite-weather-meter-with-applied-ballistics, you don't have to adjust the altitude... even if you mess with the altitude in the weather side of the meter, it will not effect the ballistic side. And yes, on a baro weather meter, even if you are sitting at your desk, it will move around with pressure changes. Here is a great article on understand baro / altimeters as well as some videos on setting your Kestrel meter: https://kestrelmeters.com/pages/understanding-pressure-altitud-and-density-altitude