HOW TO measure the velocity of a bullet

[VMFn542bob]

HOW TO measure the velocity of a bullet.
When I began target shooting in the 1970s chronometers available to me started at about $2000. I didn't have one, always planned to make one, but never had the time.
In 1970 chronometers used mechanical switches to start and stop an electronic counter. The switches were two sheets of foil placed close to each other.
When the bullet traveled through them it completed an electrical connection and that that started the counter.
A short distance away was another switch that stopped the counter when the bullet passed thorough that one.
The main difference between chronometers of the 1970s and today is technology changes in the switch.
The inexpensive chronometers available today, for about $100, use much the same technique but with the technology available today.
I have a CHRONY BETA chronometer. It has switches that are operated by light.
A change in light intensity produces a change in an electrical signal which is fed into an electronic amplifier and used to start and stop an electronic counter.
To accomplish this a focusing lens is placed above a light sensitive transducer and with light above it, usually sunlight, anything passing between the light source and the lens will produce a moving shadow.
The shadow is translated to an electrical impulse and that is used to start and stop a counter.

Technology, like bullets, moves way too fast for old retired guys like me to keep up. But I stand back and marvel what these young engineer minds keep coming up with.
If you don't already have a chronometer go out and buy one. You won't regret it even if you don't reload.
They are a heap of fun and can be used to measure the speed of almost anything that passes over the switches (without hitting them of course).

Question: What's Faster Than a Speeding Bullet?
Answer: The PVM-21 chronograph that take it's picture.

Germany’s Werner Mehl is the talented engineer who created the PVM-21 infrared chronograph, in many respects the most sophisticated ballistic speed-measuring system currently available to the general public.
Werner runs a company, Kurzzeitmesstechnik, which specializes in high-tech ballistic measuring systems and ultra-high-speed photography.
Werner has engineered camera and lighting systems that can literally track a bullet in flight, millimeter by millimeter, with eye-popping resolution.
Werner employs digital cameras that record up to 1 million frames per second, with effective shutter speeds as fast as 1.5 nano-seconds.
The videos produced by Werner’s systems are amazing.
This 10-minute video shows the impact of projectiles on various targets, recorded at 1 million frames per second.
(I found that muting the sound allowed me to concentrate more on the video but some may enjoy the music and not be distracted by it.) Enjoy !

http://www.youtube.com/watch?v=QfDoQwIAaXg

[Frederick]

Mesmerizing!

[Craftsman]

Very cool to watch!

[MXLMAX]

Aren't those bullets spinning with a Lefthand twist?

[VMFn542bob]

Originally Posted by MXLMAX

Aren't those bullets spinning with a Lefthand twist?

You have a good eye. Yes, some of those bullets are going the other way, but the "other way" depends on what your favorite gun is. Rifling twist can be LEFT -or- RIGHT, and also GAIN TWIST, in either direction. (You would not be able to discern Gain Twist from looking at the bullet while it's traveling). The bullet doesn't care which direction it rotates. Accuracy is ensured if it's rotating at the right speed (revolutions per second). Before this technology arrived, very few people have actually been able to see that bullet spin. High speed photography has come a long way with the introduction of digital photography and VERY FAST electrical switching devices.

[OldEyes]

Scary smart - Anyone who can figure out how to hit a bullet in flight is pretty darn smart!

[Unclenick]

Naw, You just stand in front of the gun being fired. Not sure I'd call it smart, though.

Seriously, though, those pictures have been around for awhile, but are still fun.

[snellbaker]

Thanks for the link and the explanation.. but a minor correction. A chronometer is a very accurate clock while a chronograph is the device you are talking about. I also have the Chrony Beta and love it. While not even in the same league as Werner's PVM-21, for the average shooter it is certainly a valuable tool. Thanks,

Art

[X Hunter]

At 5:00 or half way in the film, you can see the rifle bullet is not stable. It keyholes the cube of jell and exits nearly base first.

[Unclenick]

Snellbaker,

A lot of the instruments back in the 50's, 60's and 70's were ballistic chronometers. Basically, you would use a breakwire or foil glued to two sides of a piece of cardboard (so the bullet would make a short circuit connections in passing through) to start the clock. A second identical screen would stop it. The readout would be in microseconds.

You would then have to use your new fangled $150 four-function gee-whiz pocket calculator gadget to divide the resulting time by the number of feet spacing between the screens, then divide that result into one to get bullet speed in feet per second. It was only the later advent of cheap, low power microprocessors that made it possible to have the instrument handle that math on top of making the measurement.

The advent of fast phototransistors and PIN diodes also eventually made economical skyscreens possible to replace the electro-mechanical ones that get shot up, though they're not always more accurate. The electro-mechanical screens don't care what the light conditions are and aren't confused by muzzle blast.