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

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SkeeterHawk

SkeeterHawk

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Oct 23, 2021
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Florissant, Colorado, United States
I'm just wondering if anyone has ever tried using an FX Chronograph in reverse and shot toward it? I was wondering if it could be used to calculate the ballistic coefficient of the projectile. I guess if it doesn't work in reverse that you could turn it around a few feet from the target and I feel that it probably would read the results.

Results of BC Testing from Inside this thread:
  • JSB 15.89gr
    • Muzzle = 877FPS
    • 25 Yards = 744 (Calculated BC of 0.019)
    • 50 Yards = 704 (Calculated BC of 0.0284)
  • FX 18.1gr
    • Muzzle = 879FPS
    • 25 Yards = 792 (Calculated BC of 0.02998)
    • 50 Yards = 725 (Calculated BC of 0.03245)
  • H&N Baracuda Match 21.14gr
    • Muzzle = 867FPS
    • 25 Yards = 804 (Calculated BC of 0.0414)
    • 50 Yards = 747 (Calculated BC of 0.04195)
 
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To update this thread, even though I can't spell "FX Chronograph", apparently, you can NOT shoot toward the FX Chronograph and get it to read. It just sits there with a dumb look, not knowing what happened. That said, if you place the Chronograph 3 or 4 feet from a target, it will read it just fine and you can calculate BC all day long. I did it both at 25 yards and at 50 yards. I left my phone out at the distance, but behind a tree or something to make sure it is safe. I'm shooting about 4-5" above the Chrony to get the readings. Here is a picture at 25 yards:
20230115_093100.jpg

I'm just shooting into my target above the Chrony.

Here it is at 50 yards:
20230115_093013.jpg


I used the BC calculators on AOA's website at this link.

My results were a little surprising...at least to me. I was shooting JSB 15.89gr Diabolo. I was getting 876FPS at the muzzle, 744.4FPS at 25 yards, and 704.1FPS at 50 yards. According to the calculators, my BC was 0.019 at 25 Yards, and 0.028444 at 50 yards. I was surprised that the BC calculated to be so low at 25 yards. I expected about the same results and thought that the drag was more linear than that, let alone being inverted. Interesting... :unsure: I'm guessing now that the pellet must be stabilizing for the first part of the path, and that takes energy, so that the BC increases as it "finds it's way" and glides along. I imagine that @Ballisticboy or others WAAAAYYY more versed on this subject than I may have more to contribute on that.
 
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Privateer said:
So it detects movement away from it.
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Sure does, and that is the only direction it goes. Apparently it is only looking for the "ping" off of a projectile to increase in time, meaning it is traveling away from the unit. I wondered in this post if it was only detecting "delta" time, or if it was fixed to be going away...now we know it has to be traveling away.

Privateer said:
Have you figured out the range it can detect movement?
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No, but this would be a good experiment. I suspect that it is only a few inches, but as I have read about things interfering with the signal that are close to the muzzle, it may get reflections off of the target that would interfere with the signal. I am using logs that are irregular shaped and absorb sound by design, so they may be OK, but I suspect that a steel target may interfere with the readings...or even something just flat, like plexiglass. I don't think it would have to be electrically conductive to interfere with the signal.
 
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bigHUN said:
The echo from closed walls or close objects or shooting in a long hall or along a wall will interfere with reading.
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Thanks for the input! I've heard something similar. It makes me wonder, though. At the FX facility in the US they have a bunch of shipping containers end-to-end to test. I wonder if they have some kind of dampening material along the route? Matt Dubber shows it a lot in his review of the Panthera, so I'll have to watch that again and see if there appears to be something along the flight path. Perhaps it only needs to be the first few feet?
 
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bigHUN said:
Do you know why? and what is the difference between these two?
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Great point, and none better expressed than by the picture I posted. Makes your point clearly. That is an echo-chamber, so the radar would lose its mind, while the optical system in the Caldwell would be in optimal conditions, out of the sun and all that.

I thought that it was a little ironic to see a non-FX Chronograph being used at FX. We know the reason, don't we?
 
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I don't want to derail the thread, but some readers may find it informational.
During my 15-18 years of archery competition shooting I had my own chronographs from all Brands on the market and there were numerous times I had multiple units in same time. Also at my club we collected many more chrony's and we shoot them same way side by side. In those many years - I can confirm - we did not find two showing numbers 100% the same.
I told you this my story don't try to look for a perfect machine, pick one - and stick with it.
As from the discussion above, there is a simple reason why the guys shooting inside a container with an optical sensor. So you have two options in front of you, pick one that best suits your game.
 
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Privateer said:
Have you tried shooting past the chrony as it faces you?
That way the pellet would be going away from it
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Thoughtful question, as always, @Privateer. OK, let me get this straight...so keep the chrony at 5' from the target, but have it face me (the shooter) than the target? The short answer is "no", I haven't tried that. Since there is no transmitter/receiver on the back of the unit, I doubt that it would be able to see it, but I'll plan to "give it a shot" the next time I am playing with this stuff. Thanks again for the idea! (y)
 
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I changed my Crosman 2240 mod over to shoot FX 18.1gr pellets, which is what it likes better than the JSB15.89gr pellets that I shoot most through that gun, and I noticed that I had half as much drop at 95 yards using the FX as the JSB. I figured that I would reconduct the experiment to calculate the BC on these pellets by putting my Chrony and phone out at my targets.
  • At the Muzzle:
    • 879FPS
  • At 25 Yards:
    • 792FPS - Calculated BC = 0.02998
  • At 50 Yards:
    • 711FPS - Calculated BC = 0.02947
So, these pellets have a much more consistent BC than the JSB15.89gr. Also, the JSB had significantly lower BC at 25 yards at 0.019. All of these "clues" would make me think that the irregularities in the skirts of the JSB lead them to lose more energy initially until they find their way, where the FX have a more shallow depth of the skirt and a more "blunt" trim on the back of the skirt, so they aren't so "sharp".

I suspect that this may have more to do with the center of gravity that @Ballisticboy has mentioned in the past changing the BC of the pellet more so than the shape and trim of the skirt.

I need to do this same thing for the H&N Baracuda Match that my Avenger likes so much. I suspect that it will be similar to the FX that I just tested.

Anyway, I just thought that I'd post this little data-point.

Happy Shooting!!

Jonathan
 
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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.
 
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