UE4 C++ Shoot through crosshair (or any other screen point)

ShootThroughCrosshair.cpp

const APlayerController* PlayerController = GetWorld()->GetFirstPlayerController();

// Get viewport size
int ViewportSizeX, ViewportSizeY;
PlayerController->GetViewportSize(ViewportSizeX, ViewportSizeY);

// Deproject screen point
FVector ShotStart, ShotDirection;
PlayerController->DeprojectScreenPositionToWorld(ViewportSizeX * 0.5f, ViewportSizeY * 0.5f, ShotStart, ShotDirection); // Assuming crosshair is in screen center
ShotStart += ShotDirection * 100.0f; // Offset a bit so that shot starts from gun end
const FVector ShotEnd = ShotStart + ShotDirection * 99999.9f;

DrawDebugLine(GetWorld(), ShotStart, ShotEnd, FColor::Green, true);