Labrabaco: a G7 BC calculator from Labradar tracks

FromMyColdDeadHand

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Wow, really interesting.

Specifically talking about 22lr subs, 1040fps, 40gr. There is a move towards higher twist barrels- and it is beyond me, but I thought that the twist would/could affect the BC. We are looking for 200yards+. To me at least, at about 175yards a beast comes and starts to flick those rounds. I think by the stability calcs, the 1x16 is too slow theoretically. Maybe for shorter and supersonic it works fine. I just have anecdotal differences right now, but it seems the 1x9 holds better groups At 200.

Also, if i set up one of those optical velocity readers at a longer distance, like 100 or 150 yards, Would that help?

I was just looking to find a BC to put into ballistic calc. The effect of the twist was just an interesting question.

What are the units that the labadar should be run? Feet or meters distance/speed?
 

ptosis

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re: precision of 16" vs. 9" rifling – honestly I could not detect any significant difference. I mostly shoot the subsonic 40 gr ammo (to avoid the unpredictable transonic), and up to 500 m different good .22 rifles shoot pretty much the same. In terms of precision, different rifles seem to prefer different bullets (yet they all seem to agree on the bloody expensive Lapua), but I am not sure I am a good enough shot to really make a qualified statement.

re: another chrono at a longer distance – that is how I used to obtain and verify BCs in the past (quite successfully, albeit tediously). A magnetospeed under the barrel, and another velocity value at a known distance = the recipe for success. It is slightly less accurate than velocity decrease with time of flight, but largely good enough for all practical applications.

Problem is: sooner or later the far chrono dies by bullet wound. The only exception is the Steinert SuperChrono, which you can put behind something bulletproof, but it is extremely finicky to set up correctly (because it is extremely sensitive to angles of sight and of trajectory). Another possible solution is the shotmarker (cf. "one shot ST"’s experiments higher in this thread), which I personally did not test, but I am not hearing particularly convincing things about the velocity measurements precision.

The only reason why I started coding this whole Labrabaco thing is because of simplicity and reliability – you point the device to the target, you make sure your barrel is at the right distance from the radar box, and you simply shoot. And BC comes out of it.

re: units of measurement – it really does not matter (as long as distance is not measured in feet, which I did not properly test, because I cannot think in these weird units). Velocity in fps or in m/s, distance in m or in yd, the rounding errors are quite insignificant.

re: "just looking to find a BC to put into ballistic calc" – if you are talking specifically about .22 LR, you should perhaps wait for the next release. The G7 model is definitely not the way to go for round nose lead projectiles typically used in this calibre. The drag profiles, especially in the trans- and subsonic where the interesting .22LR stuff happens, are totally not the same. I have found some reasonably accurate Cd tables for the RA4 model (which is specifically tailored for typical .22LR ammo), and ordered a couple of bricks of [bloody expensive] Lapua ammo, which has the advantage of perfectly known trajectory. The next version will produce also RA4 BCs, which should address your (and mine) rimfire concerns way better than G7.
 
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ptosis

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v.0.8 is out, now with the taste of RA4, G1, and, while I was at it, G8.
(The default is still G7.)

Still at the same place: https://bc.geladen.ch/labrabaco/labrabaco.html

All you ever wanted to know about long-range ballistics of your rimfire trainer...

JBM and Strelok Pro (probably some others too) understand RA4 BCs.
Coming soon to Plan 33 (alas, not for the metric-impared).

Caveat: I did not test RA4 model results very extensively; would very much appreciate any feedback, especially from those who use Lapua ammo.

Enjoy.
 
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6.5SH

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v.0.8 is out, now with the taste of RA4, G1, and, while I was at it, G8.
(The default is still G7.)

Still at the same place: https://bc.geladen.ch/labrabaco/labrabaco.html

All you ever wanted to know about long-range ballistics of your rimfire trainer...

JBM and Strelok Pro (probably some others too) understand RA4 BCs.
Coming soon to Plan 33 (alas, not for the metric-impared).

Caveat: I did not test RA4 model results very extensively; would very much appreciate any feedback, especially from those who use Lapua ammo.

Enjoy.
Very nice!

With a 100 shot session of SK Standard Plus, 96 out of 100 valid tracks with the default filtering options.
Results for G1:
BC standard deviation: 0.011974951571587884
Average BC = 0.1302057202657062
SK's published G1 BC is 0.132
 

ptosis

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Very nice!

With a 100 shot session of SK Standard Plus, 96 out of 100 valid tracks with the default filtering options.
Results for G1:
BC standard deviation: 0.011974951571587884
Average BC = 0.1302057202657062
SK's published G1 BC is 0.132
Cool! That is very close to the manufacturer's data, and certainly close enough for all practical applications.

Did you have a chance to shoot longer distances (e.g. 300+ m/yd) with this cartridge? How does the trajectory compare to the BC numbers?
 

6.5SH

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Only on steel that I can't physically access. Using the SK stated value of .132 Strelok has been on to 400, at 512 impact was 1 full mil low IIRC.
 

one shot ST

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Some screenshot about some test, LS 136 BC one match perfectly other very close to published BC, other are for SK LR same considerations
 

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ptosis

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Only on steel that I can't physically access. Using the SK stated value of .132 Strelok has been on to 400, at 512 impact was 1 full mil low IIRC.

re: 512 -- I am very curious whether the RA4 model gives more accurate predictions than G1 ?
Would you mind checking it, by setting RA4 model in Labrabaco, and feeding it the same Labradar data. Then we could see if the resulting BC, introduced in JBM or Strelok Pro with RA4 model, better fits the observed dope?
 

6.5SH

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re: 512 -- I am very curious whether the RA4 model gives more accurate predictions than G1 ?
Would you mind checking it, by setting RA4 model in Labrabaco, and feeding it the same Labradar data. Then we could see if the resulting BC, introduced in JBM or Strelok Pro with RA4 model, better fits the observed dope?
RA4 gives:
BC standard deviation: 0.005967208339059481
Average BC = 0.10735645494962978

The 512 yard prediction adds another 0.8 mils of drop so in the ball park. Will have to try it and see how the closer distances line up.

ETA:
100 & 200 show the same numbers, 300 yards adds another 0.2 mils. I will have to make a trip to a local range that has 300 yard paper to get an actual measurement.
 
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ptosis

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Some screenshot about some test, LS 136 BC one match perfectly other very close to published BC, other are for SK LR same considerations
Sweet, thank you.

I must say I am pretty glad of the results that can be obtained.
(Of course, Labrabaco is by far not as accurate as industrial radars over longer distances, but for some manufacturers (did someone say Norma? Ruag?) that can be an easy fix, and a good starting point.)
 
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ptosis

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RA4 gives:
BC standard deviation: 0.005967208339059481
Average BC = 0.10735645494962978

The 512 yard prediction adds another 0.8 mils of drop so in the ball park. Will have to try it and see how the closer distances line up.

ETA:
100 & 200 show the same numbers, 300 yards adds another 0.2 mils. I will have to make a trip to a local range that has 300 yard paper to get an actual measurement.
Thanks!

On my side, I no longer have access to anything beyond 300m until March-April, when snow melts off the roads that lead to the mountain ranges. But I will run a few tests at 300, and also do some "armchair ballistics", to see how RA4 BCs compare to Lapua's Cd trajectories; will share it here.
 

one shot ST

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yesterday, same rifle, same bullet same conditions, 4 different loads, published BC .288
 

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ptosis

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yesterday, same rifle, same bullet same conditions, 4 different loads, published BC .288
That gives an average of 0.2856978, which fits the manufacturer's data to 0.8%

Sweet! What kind of cartridge it is? And, by the way, do you run a EU-castrated Labradar, or a full-power Canada/US version?