Way to measure flight time?

[DRNewcomb]

At one club we were discussing buying an electronic target system for 600 yards (no decision, just discussion) . One byproduct of an electronic target is flight-time, since there is a microphone near the shooter to confirm that he/she shot. With MV and flight-time (I believe) it's possible to solve for BC.

This got me wondering if there are any easy-to-use (preferably inexpensive) systems to measure bullet flight-time? I can see something like a wireless transmitter with a mic at the edge of the target and a receiver with another mic near the muzzle.

I did a Google search but came up with no useful hits.

 

[DRNewcomb]

Not sure we're on the same page. I have several ways to predict flight time. I'm looking for a way to measure it.

 

[expiper]

I use the hillbilly method and klik the stopwatch when the gun craks and then when I see the splash down range,,,,wink...doing your own BC calcs is kool but the left and right will plague you more at long range,,,Roger

 

[TominSWNY]

RSI's Shooting Labâ„¢ software was the first component of the Shooting Lab system introduced in 1998. It helps shooters and hand loaders analyze loads, keep proper records, and more. Shooting Lab is much more than just another "exterior ballistics" program. Its exterior ballistics are based on methods developed at the U.S. Army's Ballistic Research Laboratory in Aberdeen, MD not 110 year old Ingalls. No other commercial shooting software has comparable exterior ballistics modeling capabilities... and exterior ballistics is less than 10% of the program!

 

[Toby Bradshaw]

If you want to calculate BC, shoot over 2 chronographs a known (longish) distance apart. The decay in velocity over the known distance is inversely proportional to BC. Since you need to have the MV to use your planned time-of-flight data anyway, you might as well just use two chronographs and skip the microphone/e-target.

 

[DRNewcomb]

If you want to calculate BC, shoot over 2 chronographs a known (longish) distance apart. The decay in velocity over the known distance is inversely proportional to BC. Since you need to have the MV to use your planned time-of-flight data anyway, you might as well just use two chronographs and skip the microphone/e-target.

But I don't have two chronographs. Also, an earlier thread showed that shooting through a series of 5 chronographs yielded considerable variation between different makes and models.

I thought that perhaps there might be a simple setup involving a wireless mic, baby monitor, etc and the audio inputs of a laptop computer to time the difference between the "bang"at the muzzle and the crack of the bullet passing the target that would give flight-time. An from that to solve for BC.

 

[Toby Bradshaw]

http://www.riflebarrels.com/articles/bullets_ballastics/measure_ballistic_coefficients.htm
http://www.loadammo.com/product/bc-calcs.htm

 

[DRNewcomb]

http://www.riflebarrels.com/articles/bullets_ballastics/measure_ballistic_coefficients.htm
http://www.loadammo.com/product/bc-calcs.htm

Yes and you can also use doppler radar (probably the best but most expensive method). I would say that measuring the height of bullet impact (drop) is probably the least accurate method. So, there are a plurality of modalities for the production of a depelted feline. I just thought that flight-time would be a simple, cheap and accurate method. This method is incorporated in Oheler's top-end commercial models via interface to electronic target systems.

 

[Lapua40X]

All you need are two stable circuits that switch on/off when they're interrupted (disturbed) to turn either on or off at either end of your test distance. http://techhouse.brown.edu/~dmorris/projects/tutorials/transistor.switches.pdf
But unless you can determine precisely that the distance between your two test points is your data will still have to be considered as having some margin of error.
A penetration or proximity switch can be used to start/stop any timing circuit. You can build a penetration switch using a couple thin sheets of copper and forget about building stable circuits.

 

[wwbrown]

You will need sensors that detect the shot and a means of transmitting the data back to a central location. At 600 yards a wired solution is expensive unless you can use an existing solution.

You could probably work up a solution using a walkie talkie at the target set up in a VOX (voice activated) mode and a microphone at the rifle. You might be able to use both the mic at the rifle and a second radio set up to receive at the same channel the radio at the target is transmitting at as inputs to the sound card. To measure the time of flight (TOF) you could look at the sound file with available software by measuring the time difference between the two peaks, one from the mic at the rifle and the other would be the one from the radio at the target. The low cost Motorola radios might work for the radios and many people have them on hand.

Another way is to use one microphone as input to the sound card and record the sound of the muzzle blast at the rifle and the sound of the round hitting the target when it is heard at the shooting location. The time difference is measured the same way as the first method, but in this case you need to subtract off the time it takes for the sound to go from the target back to the mic at the computer. You would need to estimate the speed of sound and it would be good to know the temperature and atmospheric pressure (use a good Kestrel or similar) and there are sites on the web that will estimate the speed of sound knowing the temperature and pressure.

As one of the posters mentioned there will always be error one of which is the distance but the range seems already measured out for you, if not a GOS solution with a lot satellites in view will get you very close. An additional source of error is I did not include the humidity in the speed of sound solution, the humidity does not change the speed of sound much so that is a small error.

Any way you go it is not a simple solution that allows you to shoot and look down and get the TOF but if you really want it either of these solutions should work well enough for the application.