You are my hero, I was searching for hours but setting the collision to the root of my projectile made id work! (I have a projectile setup like in the twin stick shouter tutorial)
Overlap with other pawns worked. But I could make it generate hit events when hitting was. This is needed because fast traveling bullets will not allways generate the overlap event.
So thanks again! 
by the way this official doc is very good for the rest of the fysics configuration Collision Overview | Unreal Engine Documentation