One feature of good ballistics solvers like the Applied Ballistics and the online JBM is that they will calculate and display the velocities of input bullets at different ranges. That’s obviously something the solvers must be capable of doing because it’s what enables them to describe the trajectory at different ranges.
Until recently, though, it hasn’t been possible (to my knowledge) for someone who doesn’t have access to equipment beyond the hobbyist level to easily measure and confirm such calculations themselves. The most obvious way to measure velocities at different distances is to use multiple chronographs, but that would involve extra expense and logistical and practical issues such as questioning whether the chronographs all give exactly the same velocity readings. For example, the Oehler 35P chronograph was long considered to be the top level unit outside ballistics laboratories, but although my two units gave very close readings when I tested them in tandem, they were not exactly the same.
Now enter the LabRadar chronograph. It measures projectile velocity by using doppler radar and it will provide readings to as far as 100 yards. Sometimes. Various factors affect whether the unit will actually provide a 100 yard velocity reading, but when it does, it’s possible to compare its data to what a ballistic solver tells it should be.
I haven’t recorded the readings the LabRadar unit provided for many of my velocity measurements, but below are a few along with how they compared with the calculated results provided by JBM and Applied Ballistics (AB). The AB solver is clearly the more sophisticated of the two, with features that the JBM doesn’t offer. One difference is that the AB offers a library of “custom drag curves” for many bullets. Those curves were reportedly developed by actually measuring the trajectories rather than using models based on claimed ballistic coefficients (G1 and G7). The JBM is nevertheless used by many long range precision rifle shooters, and evidently with satisfactory results.
The below LabRadar velocity measurements were of a single lot of Hornady 6.5 Creedmoor 147 grain ELD Match ammunition fired from a Tikka T3x TAC A1 rifle, 24" barrel, with TBAC suppressor. Environmental: Temperature 53°, station pressure 21.21", relative humidity 20%
The columns are 1 - LabRadar measured muzzle velocity; 2 - measured velocity at 100 yards; 3 - velocity at 100 yards calculated by AB solver and the custom drag curve for the bullet; 4 - velocity at 100 yards calculated by JBM solver using the G7 ballistic coefficient. (The velocities to compare are columns 2, 3, and 4.) The results assume that the LabRadar’s measurements are correct, and we might question why some measured velocities are closer to the calculated figures than others, but the AB calculated figures were all closer to the LabRadar’s than the JBM’s—sometimes not by much, but consistently.
2513 - 2410 2419 2423
2563 - 2464 2468 2472
2548 - 2452 2454 2458
2544 - 2448 2450 2454
2547 - 2444 2453 2457
2550 - 2453 2456 2460
This was obviously a very limited test, but it may be of interest to some.
“To argue with a person who has renounced the use of reason is like administering medicine to the dead.”
— Thomas Paine
I discussed the performance of Hornady's 147 ELD-M bullet in the long range thread in the summer of 2018 or 2019. It's been long enough now that I forget the timing. I do recall the event which started it -- the casual ELR match at Whittington NRA center. I recall you weighed in on that discussion, or maybe others related to the 147 ELD at a later times. My experience is with Hornady factory 6.5CM loads. Others in Colorado have experience with handloads in 6.5 PRC.
Hornady's 147 ELD is a very accurate bullet. Its BC is better than Hornady's 140 ELD. Hornady overstates the muzzle velocity on the 6.5CM 147 factory loads. Hornady overstates the BC on the 147 ELD.
Last I checked, JBM continues to use Hornady's overstated BC for the 147 ELD. I believe other ballistics programs also continue to use an overstated BC for the 147 ELD. As a result, actual flight at long distance doesn't match predicted flight. I've seen this first hand at the Wyoming Nightforce ELR matches, for squad members shooting the 147 ELD in 6.5CM and 6.5 PRC -- both factory and handloads. I have a few boxes of 147 ELD 6.5CM in inventory -- I use them only to break in new barrels and zero a new scope.
A better 6.5CM example of how Labradar compares to AB and JBM would be Hornady's 140 ELDM. Its predicted vs. actual flight performance is generally quite good out to roughly 1300 yards.
|Powered by Social Strata|