As I wanted to capture events very close to when they happen (like the popping of a balloon) I decided to use a BB gun. This way the sound that trigger the flash will happen “long before” the bullet hits the target and I can alter the delay (or move the microphone) to get the picture at the time I want.
This was the first try and adding more delay would give a nicer result.
As a side note; shooting indoors, in the dark, is very dangerous and requires a lot of preparation. A modern BB gun is very powerful and goes through a water filled balloon with high velocity. It may also change trajectory. I was fortunate to set this up correctly because my older son was skeptic to my initial bullet capture. It turned out he was right and I am grateful.