My custom projectile collides with its shooter, where it's not supposed to.

Basically, when I use an item to fire a custom projectile, it seems to collide with its shooter in a way where it produces the sound and particle, but doesn't deal any damage, and the projectile still flies even though its pierce is set to 0. It's irritating to have the shooting and hitting sound play at once and the particle show up in the shooter's face. Any way to fix this?