Downrange Velocity Readings

[Rook 6]

If you have sighters, not a whole lot of value. It is more for the sake of curiosity or comparing projectiles or pointing techniques.

It can be hard to understand, but small changes in BC really don't change your wind hold in F-Class. Most of the time you can't see well enough through the mirage to hold that 1/2" or less difference. What an increased BC does for you is increase your margin for a less than perfect wind call from shot to shot. That's why we test it. To ensure we aren't reducing our margin, increasing BC variation, or doing something labor intensive that has a net zero benefit.

In my new found affliction, PRS, a 1400 yard shot with no sighters benefits greatly from having a better understanding of your BC and resultant trajectory. That's why I test relentlessly.

Completely makes sense. My caveat to the question of quantifiable behavior in wind would have been, do other variables, such as distortion from mirage potentially negate any benefit from a refined BC. Bottom line is that refining BC calcs for known distance, when you have sighters, doesn’t really add benefit. I get maximizing BC to minimize impact of wind call errors but this thread confirm my assumption that refined BC wouldn’t add any benefit, for me at least in f-class.

Thanks all for the feedback.

 

[dgeesaman]

Resurrecting this a bit to add some observations:

I’ve been playing with my LabRadar downrange velocities using airgun pellets and 22LR out to 100y. So I downloaded the files from the card and viewed the series csv and the per-shot csv files.

Looking at the individual shot csv files, I can see that:
- Muzzle velocity is definitely calculated, not measured directly. The previous posters trace data showed raw data starting about 12y out and mine started around 20y.
- All velocities appear to be cheaply calculated using the distance and time of two adjacent (time, distance) points in that raw data. For muzzle velocity the reported value is reasonably accurate since the close range (time, distance) points are high quality.
- As the SNR drops with distance, the distance measurements get less accurate, causing the calculated velocities get choppy, bouncing back and forth between too high and too low.

A normal user can open the series cab and average the downrange velocities at a chosen distance and the averages will give good agreement with the ballistics. I was looking at individual shots, specifically to compare the ballistic coefficient and time of flight vs muzzle velocity. So the LabRadar downrange velocity values were not acceptable. I’ve been playing with curve fits to calculate better muzzle and downrange velocities. So far the best solution is to use a fifth or sixth order polynomial fit of the d vs t point set, and take the derivative of polynomial to calculate any velocity along the path. I can’t extrapolate or get muzzle velocity with this curve fit since polynomial fits go to -/+ infinity, but the LR does collect data out a little past 100y most of the time, giving me very good data from 50-100y.