DIY Chronagraph

Sorry, Just searched forum and there is already lots of stuff on Chronographs, I'll read that. (Should have searched first DuH!)

I'm looking at building a DIY chronograph for measuring the speed of a airgun pellet, I'm looking at using IR Tx/Rx pairs to trigger a timer to measure the time between triggers and maybe transmit via RF to a remote display.

Anyone done anything similar, I'm thinking of using a reflective Tx/Rx pair and fire over the top or a slot type sensor and fire in between.

Any thoughts suggestions?

Cheers.

Google the CameraAxe project which employs a chronograph add on. They use it to track the speed of projectiles (like pellets) so they can time a camera flash properly.