Calculating BC with LabRadar. It works!

[Howland]

Yesterday was not a very good day. We got good atmospheric data - or so I thought. We had both a Kestrel and Sig 2400ABS running. If the Sig "corrects" the data to sea level like your post from yesterday describes Kestrel doing, then none of it may be valid.

The worst problem is that we had two rifles. 15 recorded shots on rifle #1, 12 on rifle #2. There were a lot of shots the Labradar did not pick up. Even worse, on the 12 shots it did pick up from my rifle #2, only two measurements picked up 100 yard velocity and none picked up anything further. All captured muzzle and 50 yard velocity.

So the questions are;
Are you familiar with the 2400ABS measurement of atmospheric pressure and is it actual or corrected pressure?
If corrected can the data be used given the elevation is known?
Is muzzle velocity and 50 yard velocity only of any use to you?

Edit to add, all shots were with Hornady .338 285 gr. ELD-M out of two rifles with slightly different twist. Labradar is not mine. If the data is of any use to you, it might take a few days to obtain.

 

[cohunt]

There may be a confusion stemming from Kestrel's "creative" terminology.

There are two types of pressure measures (actual barometers can sometimes show both).

One is the actual pressure measured by the sensor at the location -- usually called "station" or "absolute" pressure -- this is what we need (because this is what defines air density at the shooting spot).

The other is "sea level" pressure. This is a calculated value, basically meaning "what would the pressure have been, if we were at altitude zero / sea level". If you actually are at sea level, station pressure and sea level pressure are the same. If you are at a certain altitude, your effective / station pressure is always lower than at the sea level, but if you know the exact altitude, you can calculate the "would be sea level" figure.

This second "sea level" pressure value is used in meteorology to compare measures of air pressure in different regions / altitudes. It is, however, totally useless for shooting. Bullets only "care" about what's happening at the shooting location.

The problem with Kestrel "creative" terminology is that they are using the term "barometric" (measured with a barometer) to designate the sea level calculated values (and not what is actually measured by the sensors).

The pressure figure that you have posted in the picture, if I correctly read the over-the-pond units, corresponds to station/absolute pressure in Colorado Springs.

(Sorry if all this stuff sounded obvious to you.)

Ok, good--- that is from a handheld weather meter at the actual shooting site, sounds like it would be useful then

 

[shinbone]

Labradar MK II Deluxe will have a built in weather station and will spit out a measured BC every shot.

just dreaming

 

[ptosis]

@ptosis Are you going to integrate this with Taran at some point?

I do not see much value in such integration. Also, Taran was my first experience with CSS and JavaScript, and a few years down the road it looks just horrible, even by my rather loose coding standards.

If/when I get to rewrite Taran, I'd rather integrate it with my trajectory / hit probability calculator (still in development) -- http://plan33.geladen.ch/plan33.html -- to directly feed it the "shooter+rifle+cartridge" dispersion.

 

[ptosis]

Ok, good--- that is from a handheld weather meter at the actual shooting site, sounds like it would be useful then

Still, Kestrel by default shows the sea-level adjusted pressure, which is perhaps one of the biggest source or errors I see on ranges in our not-so-flat country. I think models, which are purpose-built for shooting, correct this idiocy, but cheaper entry-level ones (which work just as well) default to mountaneering/aviation/phishing applications.

Anyway, I guess the key thing is to be aware of this peculiarity, and not to miss it during setup of the "user screens".

 

[ptosis]

Labradar MK II Deluxe will have a built in weather station and will spit out a measured BC every shot.

just dreaming

If my experiment proves successful, we would not need one. I tend not to trust "all-in-one" devices (otherwise people end up making Stgw57s). One tool = one task.

 

[ptosis]

Yesterday was not a very good day. We got good atmospheric data - or so I thought. We had both a Kestrel and Sig 2400ABS running. If the Sig "corrects" the data to sea level like your post from yesterday describes Kestrel doing, then none of it may be valid.

The worst problem is that we had two rifles. 15 recorded shots on rifle #1, 12 on rifle #2. There were a lot of shots the Labradar did not pick up. Even worse, on the 12 shots it did pick up from my rifle #2, only two measurements picked up 100 yard velocity and none picked up anything further. All captured muzzle and 50 yard velocity.

So the questions are;
Are you familiar with the 2400ABS measurement of atmospheric pressure and is it actual or corrected pressure?
If corrected can the data be used given the elevation is known?
Is muzzle velocity and 50 yard velocity only of any use to you?

Edit to add, all shots were with Hornady .338 285 gr. ELD-M out of two rifles with slightly different twist. Labradar is not mine. If the data is of any use to you, it might take a few days to obtain.

Awesome! Thanks for thinking about me!

The SIG Kilo device measures should be just fine; it is purpose-built for shooting, so it does not confuse the user and shows honest station pressure. It does not even have an altitude input.
(And to answer your second question for the sake of completeness -- yes, it is possible to deduce the actual station pressure back from the "sea-level reduced", but we would need to know the altitude value which the device "thinks" it is at. In my experience with Kestrels, the process would be very prone to error, as the device tries to track altitude for mountaneering and aviation applciations, and tends to "drift off" when pressure changes.)

And yes -- the data would be very very useful for me. I am not actually using the 5 distances that Labradar shows data at. Especially since the further it goes, the less reliable information is. What the calculator actually uses is the raw track files -- measure of speed and distance taken every millisecond. Labradar writes these to the SD card (and maybe also temporarily stores them in internal memory). You can get them from the smart card or through the USB cable (Labradar itself then appears as external USB storage in the computer).

I would very much appreciate if you could recover these tracks for me. Hornady will be a very welcome addition to the testing set; I mostly shoot Swiss ordnance and Lapua.

Thanks again!

Cheers,
P.

 

[ptosis]

Is muzzle velocity and 50 yard velocity only of any use to you?

As a follow-up to my response, most of the very encouraging results that I got with my calculator were obtained with 5.56mm projectiles and a EU-rated radar (which has significantly less juice than the original CA/US/AU version). The track files hardly go up to 50 meters, and the signal-to-noise ratio near the end is getting just ridiculous. So -- yes, 50 m or so of actual measures is definitely very valid data.

 

[Howland]

Data is still on the internal memory. We need to get an SD card to be able to transfer the csv files to the computer first. Stores are closed today for the Thanksgiving holiday. Hopefully by the beginning of the week we will be able to get it.

 

[ptosis]

Data is still on the internal memory. We need to get an SD card to be able to transfer the csv files to the computer first. Stores are closed today for the Thanksgiving holiday. Hopefully by the beginning of the week we will be able to get it.

Super! In the meantime, you can simply plug the USB cable which came with the appliance -- it could act as the data interface, in case track files were not erased from internal memory yet (in which case the SD card would not help anyway). BTW, just get the smallest volume card -- the track files (and everything else Labradar writes there) are really small in size. 2GB are enough for a lifetime.

But I also understand that on Thanksgiving weekend you guys may have cooler things to do than catering for some Swiss geek's desires

Thanks again, and happy Thanksgiving!

 

[entoptics]

... digging out this old thread, to add to the original topic.

I am now developing a fully automated Web-based tool (free and open source) to do precisely that: calculate BCs from Labradar tracks.

The calculator uses the G7 model to match the recorded velocities (there's an actual ballistic engine behind), and takes into account the signal-to-noise values provided in the raw track files, to assign more or less weight to more or less trustworthy measurements.

At the prototype stage, results are very encouraging, but -- as drastic anti-COVID-19 measures here in Switzerland kicked in a month ago -- the shooting season ended rather earlier than expected. I do not have enough data to validate the approach or estimate the precision of the tool.

If you have Labradar records of your bullet tracks (the TRK folder on the SD card, "Shot XXXX Track.csv" files), recorded in known atmosphere, I would very much appreciate if you could share them.

In return,

If all goes well, I will make available a calculator producing a BC value from Labradar track files, for all to use under a free and open source license. (If all does not go well, I will produce some text describing the error sources and limitations of the approach, so that others don't waste time where I would have already wasted.)

What is needed:

1. Atmosphere: pressure, temperature and (if available) humidity. This is absolutely paramount, without proper atmo data, the rest of it is useless. An indication of the method used to measure atmo (e.g. "Kestrel 4500") would be very helpful to estimate error margins.
2. The bullet used. Preferable Lapua or Hornady, as they run their products through Doppler radar testing and provide an excellent reference (I believe Barnes and Berger do so too), but any other manufacturer with well-established verified BCs should be good too.
3. The actual track data, a ZIP archive of the whole "TRK" folder (or the whole Series folder) – at least 10 shots of the same bullet recorded in the same atmosphere. The speeds do not have to be consistent or uniform, e.g. loads testing/development data is just fine, as long as projectile and atmosphere are the same.
4. If known, the rifling twist (according to a paper published by Hornady, a rifling twist, which is very different from what is considered "average" for the calibre/speed, could explain a BC deviation of up to 2%).
5. The model of your Labradar: (a) full juice US/CA/AU or (b) castrated EU.

You can send it all by PM here on the forum (it should be possible to attach a file to a message)
or by e-mail to "guns [at] <my user name> [dot] ch"
or simply post here as attachment

Early access to the prototype will be provided to contributors.

Of course, feel free to ask any questions.

Thanks and cheers,
p.

Zip files of today's session with my virgin barreled 264 Win Mag attached below. 147 ELD-M, 143 ELD-X, and 156 Berger EOL. X-Caliber, 5R, 1:8 Twist, 24".

I've also attached the compilation file (Chrony Data 264WM.xlsx), which has the Temp/Hum from a Kestrel 3500 and station pressure from iPhone X barometer app, collected every 10-15 min or so. I used JBM ballistics, and the attached LabRadar data culling tool (LabRadar Rescue V2.xlsm) to calculate the G1 BC for each shot, which is recorded in the "Chrony Data" spreadsheet as well.

Let me know if you have any questions.

 

[ptosis]

Zip files of today's session with my virgin barreled 264 Win Mag attached below. 147 ELD-M, 143 ELD-X, and 156 Berger EOL. X-Caliber, 5R, 1:8 Twist, 24".

I've also attached the compilation file (Chrony Data 264WM.xlsx), which has the Temp/Hum from a Kestrel 3500 and station pressure from iPhone X barometer app, collected every 10-15 min or so. I used JBM ballistics, and the attached LabRadar data culling tool (LabRadar Rescue V2.xlsm) to calculate the G1 BC for each shot, which is recorded in the "Chrony Data" spreadsheet as well.

Let me know if you have any questions.

That is ÜBER-COOL!

Thank you very, very much for sharing your data!

A longread was sent in response by MP, incl. the link to the prototype calculator and the output it gives for your tracks (please let me know what you think).

We just got one step closer to the Victory of Science!

If anybody else has some tracks to share - - -

Cheers,
P.

 

[Howland]

With apologies to OP, my shooting partner finally got an SD card and installed it with the Labradar powered up which apparently deletes the strings in the memory. The data from that session is lost.

Neither of us had a great day that session so another is planned soon.

 

[akmtnhnt]

There may be a confusion stemming from Kestrel's "creative" terminology.

There are two types of pressure measures (actual barometers can sometimes show both).

One is the actual pressure measured by the sensor at the location -- usually called "station" or "absolute" pressure -- this is what we need (because this is what defines air density at the shooting spot).

The other is "sea level" pressure. This is a calculated value, basically meaning "what would the pressure have been, if we were at altitude zero / sea level". If you actually are at sea level, station pressure and sea level pressure are the same. If you are at a certain altitude, your effective / station pressure is always lower than at the sea level, but if you know the exact altitude, you can calculate the "would be sea level" figure.

This second "sea level" pressure value is used in meteorology to compare measures of air pressure in different regions / altitudes. It is, however, totally useless for shooting. Bullets only "care" about what's happening at the shooting location.

The problem with Kestrel "creative" terminology is that they are using the term "barometric" (measured with a barometer) to designate the sea level calculated values (and not what is actually measured by the sensors).

The pressure figure that you have posted in the picture, if I correctly read the over-the-pond units, corresponds to station/absolute pressure in Colorado Springs.

(Sorry if all this stuff sounded obvious to you.)

Just like you can take absolute pressure and change it to sea level, if you have the sea level pressure, and know the altitude you're at, you can change that to absolute pressure. So none of the atmos data you got was useless. Just do the math and correct it to what you need.

Like the 1011 hPa at 800m would be 918 hPa absolute.
Formula - Station pressure * ((1 - 2.25577*10^-5)*(height))^5.25588
Pressure in Pascals, height in meters.