Amateurs such as myself who manufacture ammunition often would consider the purchase of a shooting chronometer for the sake of testing the velocity of bullets of loaded ammunition. Mainly this is to compare the velocity of one the cartridge containing amount of powder vs. another. The velocity of ammunition is the unknown figure of all calculations to obtain figures such as impact energy which helps the shooter understand how much energy will likely be placed upon the target.
Shooting chronometers cost anywhere from $90 to several hundred dollars, depending on features. Most of them use 2 light screens to capture the velocity of a projectile shot from one screen to the other. One of the disadvantage of this system is that there is some uncertainty as to where the impact will be from one load to another since the velocity and resonance of the barrel changes when you vary powder charges. A shooter can incidentally hit one of the screens, which forces the unit inoperable until it is repaired or replaced.
Looking into purchasing one of these units, I found a freeware program called Softhchrono, which is a program that uses your p.c.'s built in microphone(s) as the measurement device + distance figures you input to the computer to calculate the speed between the muzzle sound and the impact sound.
I am going to try this out tomorrow. I have no idea how it compares to a light-based commercial chronograph (it is suggested to be just as accurate as cheaper commercial versions), but I expect that once the unit is set up properly, it should be fairly accurate. My general thought is that the light based chronographs would automatically have less error for multiple reasons, but I could be wrong about this. It's simple to set up - all you need is a tape measure, a p.c. with a built in microphone (or use an external microphone) and play with the software to see how well it calculates the speed of the projectile.
It is available here:
http://www.talonairgun.com/forum/viewforum.php?f=16