338/378 Wby 4.1" OAL 300gr SMK, 32" Pac-Nor bbl.
This is only a 100 yard test and might prove a little different BC numbers at 300 yards or more. The measured distance to the acoustic target is very critical and BC's can be off considerably if not measured to within 1/10 of a foot. Obviously because of this, the further away it is placed, the less error there will be with an identical distance measurement error.
Next time I'll test with two chronos, which I have not done with the 300gr SMK.
A little info on what you see here and how it works:
The acoustic target uses three acoustic microphones, each one located on a point of the triangle frame. The mach wave from the passing bullet triggers each "stop" sensor. The start screen located on the chrono rail starts the clock. With a starting and stoping point, the time of flight to target(TOF2T) is measured. With a known MV, and TOF, the downrange velocity (Vel-T) and BC can thus be calculated.
TOF is also captured in another section for each individual microphone in order to triangulate the exact bullets path/location through the three sensors.
With the use of a chamber attached strain gage peak pressure (Peak) is also calculated.
You can see the difference here is, the acoustic target relies on TOF and MV to determine BC and Vel-T, where two chronos know the exact MV and Vel-T to calculate the BC. The distance measurement of two chronos is thus much more forgiving and not nearly as critical.