I checked through your project and I believe you are running into a common issue with projectile collision. Try this:
Add a sphere collision component that is set to OverlapAllDynamic
After doing so, add an OnComponentOverlap(Sphere) node. Additionally, you need to switch the particle emitter node and destroy actor node, having them in the current order will most likely lead to a NULL pointer, which can cause complications later in development.
As you can see, you can pull the sphere close to the projectile so the projectile doesn’t get destroyed prematurely and it will give you finer control over the projectile’s actions. Please try this and see if it addresses the current problem you are facing.