To be honest, I doubt it would make it through. The projectile is a rough 8mm sphere made of a somewhat soft, lightweight rubbery plastic (which also happens to glow in the dark
) They also have a hole in the middle as they are designed to be used in fishing tackle. (I got a pack of 100 from ALDI's)
The launcher is where the real atrocities start. It's simply a basic combustion with a very long barrel and a very small chamber (Think about the size of a film canister, with the barrel being maybe 30cm long) Also, the barrel is a little too wide for the projectile.
I'm surprised the thing can shoot at all
EDIT: Also, is cavitation technically the correct term? I though cavitation was where the liquid gets to such a low pressure that it forms a bubble of vapour, where in this case it's just a low pressure zone coupled with the momentum of the water causing a bubble of air to be dragged behind the projectile.