Try the following setup:
/*Multi-cast delegate declartion inside your header file*/
DECLARE_MULTICAST_DELEGATE_ThreeParams(MyDelegate, FHitResult, bool, float);
//Must be marked as ufunction, otherwise your code won't execute
UFUNCTION()
void DoSomething(FHitResult HitResult, bool bWasBlocked, float Multiplier);
And somewhere in your C++ do:
//Delegate declaration
MyDelegate Del;
//Binding a function
//First parameter means that the function DoSomething exists inside the same C++ object
MyDel.BindUFunction(this, FName("DoSomething"));
//Executing the DoSomething function
MyDel.Broadcast(YourHitResultData,true,1.f);
For more information regarding delgates this post may provide some insight.