Not sure where my last comment went - I assume ColdSteel48 deleted their last comment and added a new one instead. In any case, the point is that you need 3 items:
- The world location of where you want the projectile to go (constrained by the view/camera direction)
- The muzzle location
- The vector that connects these two points, which is the projectile velocity (after normalizing and applying the required velocity)