True Ballistics Chrono--anyone?

[stagpanther]

I'm interested; especially since it claims to track further out than a labradar and doesn't depend as much on a good alignment to muzzle. I still haven't upgraded from my Labradar because I still value tracked ballistics beyond just the muzzle.

[taylorce1]

Going out to 300 yards would be nice, but I guess I'll just correct BC the old fashioned way. I bought the Garmin this year, and I love it. I never bought the Lab Radar because my friends that owned them were always cussing at them. I almost bought the new smaller Lab Radar, but found the Garmin for quite a bit cheaper.

I'm also interested in the Caldwell Velociradar, but it hasn't been available yet. It measures velocity at 20 yard increments to 100 yards. It trues up your bullets BC in the phone app.

[stagpanther]

Some people say Oehler is the only real way to get accurate measured BC from an instrument. I've looked at the 89--and despite all the "it's so easy" stuff--it looks pretty complicated to set up. And the bullet wave sensors at the target--I know just looking at the set-up "Yup--I'm going to hit one sooner or later."

[Unclenick]

Hornady has been doing it with commercial-grade Doppler radar for some time. Lapua did it with military Doppler radar before them. It works just fine. The Labradar’s .CSV file download function makes that easy to do if you take atmospheric instrumentation with you to the range. You need the air temperature (in shade) and relative humidity to get an exact velocity for Mach 1, and you will need the barometric pressure as well in order to calculate atmospheric density. You divide that density by the density of an ICAO standard atmosphere to get a correction factor for BCs to get the values they would have in the standard atmosphere and, therefore, to be able to compare them to the published BCs, which are for a standard atmosphere. You also need air density to be able to calculate the drag coefficient if you are doing an end-run around the whole BC thing by building an individual drag function for the bullet to use in QuickTARGET Unlimited or another program that does exterior ballistics calculations with custom drag functions.

After reading the manual for the TBC, I didn't spot the equivalent of the Labradar's function for downloading data. I don't see an accuracy specification. I don't see extreme range limitations for different calibers. They let you enter the unit's lateral offset from the gun barrel but claim when it is over 8", it only "helps" compensate for cosine error, and they recommend against doing it, which I didn't understand since the calculation of the correcting cosine value is trivial and should be accurate. The Doppler effect will keep the frequency for velocity correct, so it is only the distance from the gun you are calculating. I don't recall such an accuracy warning for the Labradar when you set up its lateral offset. That said, after looking through the manual again, the answer is probably on page 7. It shows a large angle for weak radiation strength and a narrow angle for the strong radiation space. A more focused high strength cone may be the reason for being able to work to 300 meters. However, unlike the Labradar, this unit only has a radar bullet pickup triggering mode. There is no microphone or external inertial switch triggering input, and the trigger occurs when the bullet enters the weak radiation cone and does not wait for it to reach the strong cone where it would be with the Labradar when you use that triggering mode with it. This means a larger distance between the TBC and rifle, even though entered into the device, will get triggered a greater time ahead of the bullet’s entry into the strong cone and that will make for a reading start delay which the instructions claim will mess up the precision of the muzzle velocity, which is arrived at by calculating backward from readings further downrange in both units.

The TBC has an upper velocity measuring limit of 4,000 fps, which is 100 fps higher than Labradar. This means neither is able to measure maximum velocity light bullet loads from a 22-06 or a 243 Win near the muzzle,

Anyway, the bottom line is that I would like more detailed technical information. Labradar supplies plenty.

[RC20]

And after lo many years of no competition, Garmin came out with their mini radar unit and LabRadar copied them.

But best of all (if you did not overpay like I did!) the big unit has now dropped like $140!

Actually I have no regrets, I sold a gun to buy my setup. Ticked me off to have to pay for the carry bag. Build my own base so saved there. I got the re-charge battery pack with no regrets. Boy do I hate batteries.

Some are even bundling a carry case, trip pod with the Big LR.

[stagpanther]

Great comments, thanks. I read about the necessity for adjusting to actual air density instead of standard typically used for aviation. I think the TB unit has a phone ap for downloading data from the unit. I still soldier on with my labradar--but it's showing its age and abuse/wear. Any thoughts on the Oehler 89?

[taylorce1]

Any thoughts on the Oehler 89?

At $2500 it won't find a home with me any time soon. I'm not saying it isn't worth it, but it would mean that my hunting and shooting is no longer a hobby. To be able to justify that chronograph system, I'd have to be making a living with my shooting.

I would love to borrow/rent one every once in awhile.

[Unclenick]

Stagpanther,

The Labradar lets you download CSV files containing the whole trace at 2 ms intervals, and not just the displayed velocities. I couldn't tell if the TBC had that or not.

Incidentally, the little LabradarFX unit's latest firmware upgrade includes the ability to determine G1 and G7 BCs, but I don't see that for the large unit. The big one always advertised that it was not for determining BCs, but I expect that is just because the range isn't long enough to do it in one shot. But if you are willing to shoot a lot, you can use reduced loads to get velocity loss rates over a range of lower velocities. The biggest issue will be that the Labradar at the bench will be picking the bullet up before the initial yaw has straightened out. So that leaves you to set the unit out where it is in danger, using the mode where it triggers off the return signal of the passing bullet. That seems to be the only mode for the TBC, which uses dual antennas, one of which looks to be for a weak but wide beam to trigger from, while the other is much more focussed, which explains the extended range it achieves.

On the 89, like the TBC, you have no climate input, and the BC you get is based on the average time of flight on the 89 or on the average velocity loss for the TBC and, I expect, for the LabradarFX. The video at the Oehler site makes a big point of saying they work with time as ballisticians do, but if you have the TOF and the distance to the target, divide the former into the latter, and you have average velocity. The conversion is trivial, so the whole issue isn't a serious thing to me.

The lack of meteorological data means the BC is only good for the atmospheric density you fired it in. Oehler calls this the "Fly-over BC." It's also only an average BC and is not broken down into velocity segments, as is usually done to maximize exterior ballistics software estimates of performance. Fortunately, you can take your Kestral meter to the range with you and wave it around in the air a bit to get the temperature, and it also gives you the barometric pressure and the RH and the Dew Point (an atmospheric density calculator needs one, but not both). So, you can plug that data into the density calculator and arrive at the atmospheric density in your conditions. Once you have that atmospheric density, divide it by the atmospheric density of a standard atmosphere (0.076474 lbs/ft³), and then multiply it by the BC the instrument reading gave you. Bingo, you have the BC for the standard atmosphere at the same distance. With that data, you plug the number into a standard ballistics program and see what the TOF would have been in the standard atmosphere. Many of these programs allow arguments for different atmospheric conditions but base them on the BC in a standard atmosphere, sort of doing that conversion backward to give you results for other conditions you may enter.

To see how that conversion works, imagine you get a G1 BC of 0.4000 for your bullet on a day when the Kestral's numbers and the calculator say your atmosphere has a density of 0.080298_lbs/ft³. The ICAO Standard Atmosphere has a density of 0.076474 lbs/ft³. Because your air is more dense, the bullet will have taken longer to get to the target endpoint than it would in the standard atmosphere, so the fly-by BC will be lower than it would have been in the standard atmosphere. So, you divide your density of 0.080298 lbs/ft³ by the standard atmosphere density of 0.076474 lbs/ft³, and you get a correction factor of 1.05. This means that flying through a standard atmosphere, the bullet will lose 1.05 times less speed and arrive at the target 1.05 times faster, and therefore, the fly-by BC will be 1.05 times bigger, or the fly-by BC=0.4×1.05=0.42 in the standard atmosphere. You would then use 0.42 in your ballistics program to adjust the value for different weather conditions.

Two things to keep in mind: assuming your bullet actually has different G1 BCs at different velocities, you would still have to do additional firing at different distances to work those out. However, Sierra provides those numbers for its bullets, and Bryan Litz's book of bullet BCs he's measured also has them for many bullets. So if you put one of these sets of numbers into your ballistics program and get their predicted TOF in the Standard Atmosphere at the same range as your instrument gave you its fly-by BC, you can use the ratio of the two times to adjust all the stepped values to get what they are in your gun. You will then have something that is a pretty tight set of numbers across all velocity ranges.