How to calculate FPE at distance?

I think I figured out why you could not get your fx chronograph to work. Speed, you did not take into account how much lost in speed you would lose. At first I could not understand why it would not work. Then I realize you may not have change the reading speed to sub 12 UK speeds. As they read lower speeds. Or you may not be aware of how quickly a pellet can slow down in just 30 yards. I put the fx chronograph about 3 to 5 feet away from the target and my phone about 25 yards from that. Then I shot at 33 yards away about 840 fos I think. 🤔 this is what I got.

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Allen
 
I think I figured out why you could not get your fx chronograph to work. Speed, you did not take into account how much lost in speed you would lose. At first I could not understand why it would not work. Then I realize you may not have change the reading speed to sub 12 UK speeds. As they read lower speeds. Or you may not be aware of how quickly a pellet can slow down in just 30 yards. I put the fx chronograph about 3 to 5 feet away from the target and my phone about 25 yards from that. Then I shot at 33 yards away about 840 fos I think. 🤔 this is what I got.

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Allen
Well I'll be darned. I think you are absolutely right! I'll go about it again tomorrow and set it at a lower velocity. I'm kind of excited now to actually figure out my BC without buying new equipment! Thanks for the tip
 
There are so many variables with the arithmetic most of which are only wild assed guesses that your results will very likely be meaningless. The only way to do this accurately is to use multiple chronographs measuring the same pellet at several distances at the same time. If you can arrange that, you can also calculate the real ballistic coefficient for you, your kit and your environment. Anything less is a WAG, but maybe that's good enough. In the end, you really do not care about numbers. The only thing that really matters is where your pellet hits at various distances. So measure that and be done with the rest.