AirgunNH, thanks for the data!
The
JBMBallistics.com caculator allows to enter atmospheric data (with barometric pressure having the biggest effect...). The PyramydAir calculator does not consider atmospheric conditions....
I'm getting a BC of 0.081, with an assumed standard pressure at MSL of 29.92hg, and the G1 drag function (I hope I can attach the screen shot).
ChairGun (for which I would need my laptop) also calculates the GA drag function, a little more appropriate for airgun pellets.
Why the difference? (1) Every barrel is different.... (I hate this reason.)
(2) Errors in the input data produce errors in the output.... E.g.:
—1 yard error in the actual range between the chronographs: —> 0.001 error
—If your barometric pressure (calculated for MSL) was actually not 29.92, but 28.92: —> 0.002 error
—9 fps total error in the averages of the two velocities (@ muzzle and @ target): —> 0.01 BC error, so instead of 0.080 you'll get 0.090
This velocity error is "easily achieved"
(esp. with only one chrono, and using only a small amount of shots)...: Our guns often have an extreme spread of 10fps muzzle velocity, some a lot more. Now all you need is that, by coincidence, the first 5 shots are around 4fps higher than the average MV, and the next 5 shots 5fps lower. There you get a 9fps difference, and that offsets your BC by 0.01.
—Now, all these possible errors add up....
Thanks for sharing your data!