Calculating Bullet Speed Using Audacity


Max and Phildog hit the shooting range this weekend to see if they could accurately measure bullet speed using Audacity. Using Audacity to examine the wave form they can determine the time between the shot being fired and striking the target. This time needs to be adjusted based on the known distance to the target. They’ve got data from quite a few different guns, but this is just a test run and they’re still improving their technique.

36 thoughts on “Calculating Bullet Speed Using Audacity

  1. Let’s not forget that modern sound cards have pretty cool sampling rate (44100 Samples/sec) so it’s a very accurate method of measuring stuff. I used the same concept 8 years ago for measuring body temperature by slowly injecting air from the mouth to a tube (8cm length, 0.7 cm diameter, closed bottom) and measuring the frequency of the whistle with Gold Wave. The principle is that the produced sound is based on the shape and size of the tube and the air temperature. I’ll see if I can find any notes.

  2. Doesn’t seem like the guy factored in air-resistance. Note the speed of the Rem. Fieldmaster .22 — for the 32m object, it had a speed of 355m/s, yet for the 64m object, it ended up with a speed of 174-178m/s. That’s almost a 50% drop in speed over twice the distance.

    Now that I think about it, that wasn’t the point of his exercise. He just wanted to measure average speeds. Had he wanted to test muzzle velocity, or the drag coefficient of a particular bullet, would he need a few more extra calculations.

  3. #6, I agree, but I guess we should also consider the amount of effort needed sort through reader submissions to post daily links.

    I hope that they bring them back, or there should be a section for user submitted hacks.

    Hackaday, Slashdot, and Engadget aren’t enough; I’m starting to run out of stuff to keep me from falling asleep at work;)

  4. RE #7: We were planning on doing a muzzle velocity extrapolation using a velocity curve for various distances, but the range got too crowded. Since it was just a proof-of-concept anyway, we’re saving that for next time.

    RE #3: You could use this technique as a sniper finder, but you would need either several directional microphones or to hear a lot of shots from the sniper. Your choice. :)

  5. Well Mark Question, LadyJake and jake, you can all leave now and I won’t miss you at all.

    The hack is rather interesting, I wonder how accurate the timing marks are in audacity?

  6. Ok, i admit also, I realllyyyyy miss hackaday links, I want to help make it better but dont know how, I feel as if everything has been hacked that can be hacked. oh well please oh please put links on 2morrow! im really board at school and so is my teacher he loves this site!

  7. #5 there is actually software that you can get that will use your soundcard as an o-scope. i downloaded this the other day and was actually somewhat usable. although your limited to 20hz to 20khz and the sample rate of your soundcard, but its cheap :)

  8. Hook 3 or more soundcard inputs to a computer and do a bit of triangluation, and compinsate for air resistance and yuo could come up with a tracking device for gun shots, i wonder if would actually be usefull to anyone thogh

  9. For all complaining about how hackaday is not so great anymore, try submitting your own hacks and contributing! We’re (we being me and two other people) are almost done with hacking a 1967 bridgeport cnc mill’s punch tape reader into something can be controlled though a computer with the gcode standard. When we finish, the first thing I am doing is submitting the website here. There are plenty of hacks that havn’t been done, you just have to go out and do them.

  10. Just like to say that I love this hack.

    The beautiful thing about this is that it uses ordinary technology and does something that most people would consider undoable without special tools. Kudos to you bulletmen.

  11. mike: i totally agree with you but i think the issue is more that the variety is lower without the links. normally when there is the hackaday links there is at least one link that i find really cool. now it is kinda hit and miss. while i still appreciate the hacks, turntables and such just do not interest me very much. is it possible that we have already seen all the hacks that are currently on the interweb? and now the only ones that havent been posted are the ones that havent been done.

  12. Well, #30 I’m not complaining but I have slowed to visiting h-a-d to once every couple weeks. I actually have submitted some hacks but none have ever showed up here(*), so at least the ball’s not in *my* court!

    (*) It’s a little funny to think of, but perhaps my hacks got blacklisted because I made a comment along in my first submission about being unable to enter capitals into the forms (and questioning the general lack of capitals on the site – but not in an jerkish way), and at least one of the URLs I submitted was case-sensitive (being on a Unix host).

  13. RE: ALL CAPS – actually, if you view the html source you will see your caps are being sent down to your browser. It seems you may need better control of your browser software? :-) If you copy and paste truerta in the above post and paste to your text editor it will have RTA in caps. Javascript…

  14. #34… Not javascript. It’s CSS. If you look at hackaday’s css file you can see it has text-transform: lowercase; which does what it says. The rest of your comment is correct, though.

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