SpudFiles

I came across this site and thought i'd share. If you don't have a chrony and don't want to spend 90 bucks on one, maybe you have a PC or laptop laying around...oh wait, you must! Get a long cord to the microphone if you need to. Run it through your bedroom window or whatever. I myself will probably try this with my laptop.

http://arxiv.org/ftp/physics/papers/0601/0601102.pdf

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The MIC method is simple but it really isn't the best. Too much uncertainty in exactly which peaks are which. In addition, the speed of sound (SOS) isn't a constant. Over the normal temperature range that a chrono might be used the SOS changes by ~5%. Phototransitors (or photodiodes) work much better and eliminate the dependence on the SOS.

The only real advantage of a MIC based method is that the line of flight of the projectile doesn't have to be aligned with the detector(s). However, if you mount the chrono detectors directly onto the gun's barrel then the alignment problem of an optical detector goes away.

i like the poormans chrono with the coke can, it only works for bbs though

Yep, its been done. The signal is very messy, and there is more calculation involved. You can see mine on my site, under data acqusition. Under coilgun/shots, there is a calculator that makes it easy. Just put distance of two peaks, and the detector spacing.