If you need your projectile to not collide with who fired it, then you plug GetInstigator in to the IgnoreActorWhenMoving node on the projectile. This, of course, requires you to assign an instigator when spawning the projectile in the first place.
On your pawn:
If you spawn the projectile on your character blueprint, then plug in Self as the instigator.
On your projectile:
