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Do you have the following?
Computer w/ a mic?
Microphone for computer? (not integrated ones)
Measuring tape? (Atleast 2m distance)
2m distance?
Target box (with hard backing)
If so what you could do is setup a distance (make it atleast 2m), one end will be the targetbox while the other end is the muzzle. Make sure where the bb hit is exactly 2m (or whatever distance you use)
Now place your microphone exactly 1m between the target and the muzzle (but not in line of fire)
Use computer recording program like Audacity set up a recording and shoot it. The first spike in sound indicates the bb leaving barrel while the second spike is the bb hitting the target.
Highlight the time between two spike, find the time difference (generate silence feature will give you a second)
Now that you have the distance and time, you can derived velocity. (Velocity = distance/ time) If you can derived velocity at 0.25g you can find the 0.2g velocity via (Energy = 1/2*mass*velocity^2)
If you're meausurement are off, the result will be off, but I found this more accurately than Madbull chrono.
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