LabRadar Benefit: Estimating BCs

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Legionnaire

Legionnaire

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If you're using a ballistics calculator or app to calculate firing solutions or trajectory tables, you need the bullet's diameter (caliber), weight, and ballistic coefficient (BC). What if you don't know the BC?

I found myself in that situation. I have a bunch (and I mean a bunch) of old Remington .243 caliber 80 grain PowerLokt HP match bullets. They have been out of production for a long time and I couldn't find a ballistic coefficient listed for them anywhere. Then it occurred to me: my LabRadar captures a projectile's velocity at up to five distances beyond the muzzle; I should be able to use those data to calculate (or at least estimate) the ballistic coefficient.

I already had some .243 AI case-forming loads built with these bullets, so a short range trip produced the data I needed. I then sat down with JBM Ballistics' trajectory calculator. I plugged in all the data I could to get as accurate an estimation as possible. That included the info I had about the bullet, as well elevation, air pressure, humidity, etc. I set the calculator's range increments to match the reading distances in the LabRadar data--in this case 15 yard increments (15, 30, 45, 60, 75). I found the BC for another 80 grain bullet to use as a starting point. Then entered my measured muzzle velocity and hit "calculate."

The resulting table showed the projected velocities at each of my measured distances. They were slightly higher than the velocities measured by the LabRadar, indicating that the test BC was too high. So I played with the BC number until the projected velocities matched the measured velocities. I used the data from several additional shots to confirm. So now I have a pretty good BC to use in my ballistics app. I should have opportunity to shoot at 500 yards on Saturday, which will let me confirm.

I really like the LabRadar.
 
I've been dithering between the Lab Radar and the Magnetospeed, partly because both have the advantage of being set up at the firing line rather than downrange. I'm leaning toward the Lab Radar because it offers more features and would be suitable for handgun load development.

If you've tried this, could you tell me how well the LabRadar functions in an indoor range situation?
 
@Dave DeLaurant, sorry, no first hand experience using it indoors. Others report it works fine, but I can't confirm.

FWIW, I sold my Magnetospeed (which I liked) to help pay for the LabRadar. No regrets.

ETA: I bought one of JKL's LabRadar Triggers, which really cut down on missed shots and the hassle of setting up.
 
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I think it would be more accurate to call it calculated BC vs estimated... being that number is an average over the distance traveled due to an ever changing speed and wind resistance, close is good enough. Your shooting app or program does these advanced calculations and you will be able to make adjustments toward a better bc over time. Significant cold bore information collection would be of benefit in the most critical of these data sets.
 
Dave DeLaurant said:
I've been dithering between the Lab Radar and the Magnetospeed, partly because both have the advantage of being set up at the firing line rather than downrange. I'm leaning toward the Lab Radar because it offers more features and would be suitable for handgun load development.

If you've tried this, could you tell me how well the LabRadar functions in an indoor range situation?
Click to expand...


90% of my shooting is indoors with handguns and have zero issues even with all lanes shooting.
 
If you install an SD card in you LabRadar it will store an addition data file for each individual shot in a subdirector under the string data. This file contains range, velocity, and signal-to-noise ratio data for each shot at 1 or 2 milli-second intervals (depending on rifle vs pistol mode IIRC) going down range until it looses the bullet (return signal gets to weak). This data is very helpful for backing into a BC for a bullet.

http://jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi

This is calculator from JBM Ballistics takes two velocity at two know distances apart and will give you the best fit BC for a chosen drag model (G1, G7 etc). Basically the same thing OP did with JBM trajectory calculator but you only have to press one button and it does all the work to find the BC that fits the inputted data the best.
 
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You should keep in mind that BC is velocity dependent. The bc of a bullet from 0-100 yards isn’t the same as from 500-1000 or 1500-2000 yards.

it’s typically higher the faster the velocity. So labradar May measure your bc to 100 and it may be correct. But if you try to use that to predict flight at 500 yards your bc will be high which means your impacts will be lower than expected.
 
If you want to be accurate in your program you need to correct it to standard conditions as well.
 
Magnetospeed hangs off the end of the barrel -- with dramatic effect on barrel dynamics/POI/group size.
(Plus) it only handles weapons w/ barrel lengths/muzzle physical designs that support its mounting there.
That, and muzzle velocity only... vice continuous tracking downrange.

LABRADAR is expensive, but it opens the world up for very serious handloaders who work across multiple
loads, bullet designs, powders, and firing platforms.

,
 
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Idk I’ve been a pretty serious hand loader and competitive shooter in high power 3gun and PRS for twenty years and I’d take a magnetospeed any day over a labradar even if they were the same money which they’re not even close. I haven’t found a dramatic difference in group size either.
 
taliv said:
You should keep in mind that BC is velocity dependent. The bc of a bullet from 0-100 yards isn’t the same as from 500-1000 or 1500-2000 yards.

it’s typically higher the faster the velocity. So labradar May measure your bc to 100 and it may be correct. But if you try to use that to predict flight at 500 yards your bc will be high which means your impacts will be lower than expected.
Click to expand...

In theory BC was create so that it was a single number correctly scaled the coefficient of drag (that is a function of velocity) over the entire velocity range. The problem is we only created a handful of ballistic models (G1, G2, G5 etc) and if your bullet's form factor is too far from the Gx model's form factor than the coefficient of drag will not be correct scaled by the BC over the entire velocity range. For what ever reason most shooters have only ever heard of G1 and G7 models and with many of the new bullets these models (and the few others that exist) simply do not correctly capture the coefficient of drag over the velocity ranges. Rather than create new models for these new bullets everyone has instead simply shoe-horned it by using multiple G1 or G7 BC's over narrow velocity ranges to force fit the drag model. Not sure why the industry is so resistant to a new drag model especially for the new VLD bullets.
 
Legionnaire said:
If you're using a ballistics calculator or app to calculate firing solutions or trajectory tables, you need the bullet's diameter (caliber), weight, and ballistic coefficient (BC). What if you don't know the BC?

I found myself in that situation. I have a bunch (and I mean a bunch) of old Remington .243 caliber 80 grain PowerLokt HP match bullets. They have been out of production for a long time and I couldn't find a ballistic coefficient listed for them anywhere. Then it occurred to me: my LabRadar captures a projectile's velocity at up to five distances beyond the muzzle; I should be able to use those data to calculate (or at least estimate) the ballistic coefficient.

I already had some .243 AI case-forming loads built with these bullets, so a short range trip produced the data I needed. I then sat down with JBM Ballistics' trajectory calculator. I plugged in all the data I could to get as accurate an estimation as possible. That included the info I had about the bullet, as well elevation, air pressure, humidity, etc. I set the calculator's range increments to match the reading distances in the LabRadar data--in this case 15 yard increments (15, 30, 45, 60, 75). I found the BC for another 80 grain bullet to use as a starting point. Then entered my measured muzzle velocity and hit "calculate."

The resulting table showed the projected velocities at each of my measured distances. They were slightly higher than the velocities measured by the LabRadar, indicating that the test BC was too high. So I played with the BC number until the projected velocities matched the measured velocities. I used the data from several additional shots to confirm. So now I have a pretty good BC to use in my ballistics app. I should have opportunity to shoot at 500 yards on Saturday, which will let me confirm.

I really like the LabRadar.
Click to expand...
Since LabRadar can take the velocity of the same bullet continuously out to 100 yards, you (or the link below) should be able you calculate the BC directly.

https://www.jbmballistics.com/cgi-bin/jbmbcv-5.1.cgi
 
taliv said:
Idk I’ve been a pretty serious hand loader and competitive shooter in high power 3gun and PRS for twenty years and I’d take a magnetospeed any day over a labradar even if they were the same money which they’re not even close. I haven’t found a dramatic difference in group size either.
Click to expand...
Curious to know how a chronograph effects group size.
 
lysanderxiii said:
Curious to know how a chronograph effects group size.
Click to expand...
With most chronographs there is no difference but with a Magnetospeed, that hangs on the muzzle end of the barrel to take its measurement, it might have an effect. Anytime you hang a weight on the end of the barrel (brake, flash-hider, suppressor, Magnetospeed, etc) it is likely to effect barrel harmonics. Testing is as simple as shooting a few groups without the Magnetospeed, mount it on the barrel, and shoot a few more groups with it and compare. Barrel harmonics being what they are, group size is as likely to get tighter as looser. Point of impact might also move depending on barrel length and contour.
 
MEHavey said:
....and your reasoning ?
Click to expand...
While both give accurate results the magnetospeed has the following advantages

1. it’s lightweight and easy to pack to the range or wherever. Has a small case but you don’t need it. Just throw it in your backpack or range bag

2. Battery is just a couple Aa or aaa I can’t remember and life is usually 2 years or so with fairly heavy use. Compared to the labradar which sucks juice so bad it will last a few hours unless you buy an external battery pack to schlep around. Preferably rechargeable.

3. I Typically shoot several different target arrays that require traversing horizontally and vertically between berms and I can do that with magnetospeed attached. Don’t have to stop and point my chronograph towards a different target.

4. and of course there’s the price.

On the other hand, as I’ve said, the one thing the labradar could possibly do that the magnetospeed can’t is calculate bc. But to do that in a useful way it would have to track the bullet out to the distances you want to shoot at. Since the labradar can’t read your velocity at 1600 yards or even 500 yards, it won’t give you a useful number. I don’t know any serious shooter that bases their calc on a bc they derived from the 100 yard velocity they measured with their labradar.

So since the labradar won’t actually do anything useful that the magnetospeed doesn’t, it should really be incumbent on the labradar proponents to explain why one should pay 2-3x the price for the privilege of carrying a heavy bulky device to the line and burning through batteries. The only legit reason is just because you want to. And if that’s the case, rock on. I’m a gadget and technology geek too. It’s a cool device. I get it.

lysanderxiii said:
Curious to know how a chronograph effects group size.
Click to expand...
As was explained above, it can change barrel harmonics.
However, on my heavy contour barrels, with a suppressor on the end already, I very rarely get a measurable shift in POI or group size. And even then we’re talking .1 mil.
Ymmv if you’re using a pencil profile but is it really that much of an inconvenience to work up your load and then chrono it?
 
It's a heck of a lot easier to measure velocities from a handgun using a LabRadar. The MagnetoSpeed worked fine with my rifles; handguns, not so much.
 
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