Or you don't do that and do it the way more efficient and simple way using VCE.
VCE is more efficient but it is not installed on every server since it is not default.
(although it should)
wait wat.
If a projectile is fired from a brick that is bigger than a 1x1 brick, it fires from a random position in that brick.
This is a 4x1 plate brick:
[_|_|_|_]
This is a 1x1 plate brick:
[_]
[_|_|_|_] fires projectile down
|
|
|
o
[_][_]
[_][_] catches the projectile
If the projectile lands on the red brick you do:
OnProjectileHit > ... execute code
Since the 4x1 plate brick is 4 times bigger than the 1x1 brick, the chances of it hitting the red brick are 25%