Can you shoot toward an FX Chrony to get B.C.?

[JungleShooter]

This is intensely interesting.

After a travel-related hiatus from shooting airguns I'm gearing up for some BC testing myself, so all this discussion is enlightening.

Thank you for continuing to contribute, Jonathan and Miles!

Matthias

 

[SkeeterHawk]

The problem with placing the FX chrony down range is that to get an accurate velocity figure you will have to shoot so that your pellet passes within an inch or so of the radar, are you feeling lucky? The radar does not know where the pellet is, all it can do is estimate a speed of the pellet at itself based on measured speeds of the pellet going away from itself. If the pellet does not pass very close to the radar, there will be angular errors giving inaccurate estimates. The radar needs to be looking directly at the back of the pellet, straight down the trajectory. This is more likely why you get strange BC values at different ranges.

Thanks for the reply! Yea, I feel pretty confident in where I am placing the shot, so I am shooting about 2" above the Chronograph the whole time. That said, I may have had a slightly different angle the last time I did the 25 yard on the 15.89gr pellets as I was shooting about 4" above that one, so I will plan to try that one again just for grins and make sure that I am pretty "flat" going over the Chrony.

Thanks again for the feedback!!

 

[SkeeterHawk]

I was getting some trigger-time on my Avenger today and decided to dedicate a few H&N Baracuda Match to the BC experiment.

• At the Muzzle:
  • 867FPS
• At 25 Yards:
  • 804FPS - (Calculated BC of 0.0414)
• At 50 Yards:
  • 747FPS - (Calculated BC of 0.04195)

One thing that was really interesting was that I left my Chrony out at 50 yards and took a couple more shots that were "near" the Chrony. I took one that was about 8" high and about 6" to the left of the Chrony, and it measured 698FPS. I took one about 4" above that one, and it read 612FPS. You know I didn't lose 140FPS, so this is indicative of a calculation error in the FX Chronograph as @Ballisticboy pointed out. So, now I have a new experiment to get to the bottom of. Is it the distance from the Chrony that introduces the error, or is the angle that it passes over as @Ballisticboy theorized, or does it have to do with the distance from the Chrony in the X-axis that introduces the error? I'd like to conduct this experiment in the next few days, but I am really busy, so it may be a week or so before I get to this. I think that it would be best to start that as a different thread addressing the calculation errors within the Chrony.

Anyway, this is another installment into my search for BC using my FX Chrony.

 

[Ballisticboy]

We found out a lot of things when we first started testing bullets using artillery Range and Accuracy (R&A) trial methods. In R&A trials, we always used two radar chronographs, which had to agree with each other to within 1ft/sec. When we switched to tracking bullets, it proved much more difficult, and we had to settle for the two numbers to be within 2-3 ft/sec. This was only possible with the two radars positioned right next to the barrel, practically touching it, and with the radars very carefully aimed to follow the trajectory. These were not FX radars, these were $20,000 radars. That is why I said you need to get your airgun projectiles to pass very near to the radar.

 

[OldSpook]

The problem with placing the FX chrony down range is that to get an accurate velocity figure you will have to shoot so that your pellet passes within an inch or so of the radar, are you feeling lucky? The radar does not know where the pellet is, all it can do is estimate a speed of the pellet at itself based on measured speeds of the pellet going away from itself. If the pellet does not pass very close to the radar, there will be angular errors giving inaccurate estimates. The radar needs to be looking directly at the back of the pellet, straight down the trajectory. This is more likely why you get strange BC values at different ranges.

He could put it behind a barrier. And then anything that was going to hit them chronograph would hit the brick wall. That would allow him to shoot very close to the chronograph.

 

[SkeeterHawk]

He could put it behind a barrier. And then anything that was going to hit them chronograph would hit the brick wall. That would allow him to shoot very close to the chronograph.

That was exactly what I had originally planned to do, but from my experiments in this thread (Things that cause inaccuracies on the FX Chronograph) I wonder how important the proximity of the shot is to the Chrony as compared to the angle that the shot goes with respect to the Chrony. It seemed to give pretty consistent results in a number of the tests, so I'll just try to keep the shot "flat" over the Chrony and maybe use a 4" log or something in front of the Chrony that wouldn't ricochet.

 

[OldSpook]

That was exactly what I had originally planned to do, but from my experiments in this thread (Things that cause inaccuracies on the FX Chronograph) I wonder how important the proximity of the shot is to the Chrony as compared to the angle that the shot goes with respect to the Chrony. It seemed to give pretty consistent results in a number of the tests, so I'll just try to keep the shot "flat" over the Chrony and maybe use a 4" log or something in front of the Chrony that wouldn't ricochet.

Yes, the problem with a RADAR system is that there is a "tunnel" the projectile has to pass through. That tunnel is not shaped like a cone. It is a "tunnel". If the pellet enters the tunnel and then deviates in any direction you will get errors because the RADAR can not get a true measurement of the distance traveled. If the projectile does not enter the tunnel, you will also get errors because the pellet isn't where the RADAR thinks it is when it gets the first reading. Either way you get errors. Just keep that pellet centered above the RADAR and as close to it as you can, and that means you need some bricks. =)