Time to break some stuff!
In the tutorial there is a part where you put some collision on your projectile, and I had some difficuties with it.
The modification made programaticaly werent taken into account, for example, I set the InitialLifeSpan, but it was not added on my projectiles until I set the value directly in the editor.
I had the same probleme with the collision, and once again I had to use the editor to set the correct collision values.
Or maybe because I was using the BP_FPSProjectile has Projectile and not the FPSProjectile directly. I should dig a little more on this matter.
Anyway, here the result, the cube was sent flying by the might of my projectiles 😀 
Nav's Workshop 