Airgun Projectile BC for Complete Dummies

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Ezana4CE

Ezana4CE

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Jan 15, 2021
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In this case I'm the dummy. This evening I tried using the ballistic feature in my Pard NV008 LRF. It was asking for data that I didn't have. To obtain the scope height I took calipers and measure from the middle of the breech to around the middle of the objective lens. Then I chronographed a shot string to get an average fps. Then I noticed that the scope asked for a "far distance" velocity. I have no way of knowing that without setting my chronograph downrange close to the target. No way am I doing that. I already shot the chrony in a shooting session this year. I'm not doing it. So what are my other options besides a Garmin, FX, or LabRadar type of chronograpgh? I'm trying to calculate the BC of the pellets I'm shooting hoping that I can eventually be lazy and not have to remember my holdovers for night shooting once I get this scope dialed in. This "far distance" term is throwing me off. What does that even mean? How far away from the rifle does the measured "far distance" have to be? Anyone else with beginner questions on ballistic coefficient fire away.
 
Hal4son said:
Which pellets are you shooting? Downrange velocity would be critical for calculating BC but if you post what you're shooting it's possible someone will have a source for that info.
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JSB King Heavy MkI and MkII. At least that's what I wanted to shoot tonight, but I'm debating on resting or maybe just shooting in my yard.
 
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I’d still like to learn do this for myself. So for the far distance parameter, are there other methods of obtaining this information besides placing a chronograph down range in proximity to the target or using a Doppler radar styled chronograph? I have no idea how fro from the muzzle and how close to the target “far distance” is supposed to be. If there’s an another thread or a link you may have that can better explain this, I’m interested in reading it. It is a tough detail to bring up in a search so far.
 
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Shoot a few test shots on paper to verify your point of impact and then place your chronograph down range. Have some confidence in your skills. Start off close like 25 yards and then slowly progress out. I shoot through my chronograph at multiple ranges out to 80 yards so that I can get the most info that I can for determining my BC. Just shoot paper first and wait for calm wind condition. I have faith in you; go for it.
Kenny
 
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Kgphotos said:
Shoot a few test shots on paper to verify your point of impact and then place your chronograph down range. Have some confidence in your skills. Start off close like 25 yards and then slowly progress out. I shoot through my chronograph at multiple ranges out to 80 yards so that I can get the most info that I can for determining my BC. Just shoot paper first and wait for calm wind condition. I have faith in you; go for it.
Kenny
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@Kgphotos I’m not sure that so have that kind of faith. However, if I do try this, I would like to know how close to the target do I place the chronograph? The ballistic calculator asks for a “far distance” but I have no idea what that means. I don’t know how far from me or how close to the target that the chronograph needs to be placed. Am I placing the chronograph 1 yard from the target with me shooting with a 25 yard zero? Further away from the target? How does this calculation work?
 
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Ezana4CE said:
@Kgphotos I’m not sure that so have that kind of faith. However, if I do try this, I would like to know how close to the target do I place the chronograph? The ballistic calculator asks for a “far distance” but I have no idea what that means. I don’t know how far from me or how close to the target that the chronograph needs to be placed. Am I placing the chronograph 1 yard from the target with me shooting with a 25 yard zero? Further away from the target? How does this calculation work?
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All that matters is that you use 2 distances to measure velocity, ideally with the same shot, but if your spread is very small, you can use 1 chronograph and shoot 3-5 shots, average em, and repeat at the 2nd distance.

One chronograph:
Shot 1-3 or 1-5: @ 1 yard between muzzle and chronograph <-- near distance
Shot 3-6 or 6-10: @ 25 Yards between muzzle and chronograph <-- far distance

Distance apart would be 24 yards if using the attached spreadsheet. Don't use any bc calculator that doesn't allow your environmental inputs.

-Matt

View attachment GA BC Calculator.xlsx
 
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When all I had were optical chronographs, and I wanted to check the far distance velocity, I would place a brick or something in front of the chronograph screen to protect the vitals. I would walk down range after each shot to check the velocity reading. A later chronograph would store shot strings, saving some walks.
 
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Exactly what Stubbers said. I use an average of ten shots at each distance. And to make it really interesting, do a few different distances and see how the BC will actually change with distance and velocity loss. The BC you get at 25 yards will not be the same as the one you get at 50 yards. They will be very close though and definitely close enough for your ballistic program to work with. It’s all fun science.
Kenny
 
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09D70035-6ABC-47BF-BB3C-32897A67A280.1608820030.jpeg
 
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Scotchmo said:
When all I had were optical chronographs, and I wanted to check the far distance velocity, I would place a brick or something in front of the chronograph screen to protect the vitals. I would walk down range after each shot to check the velocity reading. A later chronograph would store shot strings, saving some walks.
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@Scotchmo Good advice. Still working on it. Only read one shot out of the 19-shot string. About to give it a go again. I think my phone was too far away or the wood is obstructing the Wi-Fi signal.
IMG_6504.jpeg
 
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My Competition Electronics Chronograph was communicating with my phone all the way from 80 yards. I was actually amazed that it worked that far away. Maybe it is the log blocking your signal. I didn’t hide mine behind anything so I could actually see that the numbers on the chrony screen were changing with each shot. I was also using the light kit. I find the light kit to be much more reliable than just the ambient light on scene.
Kenny
 
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