Smooth camera follow return

Does the camera start by targetting a stationary bullet (a bullet in Heirarchy was dragged into the Target transform of mainCamera?) If so, it might be easier for the bulletScript to "teleport" the bullet back to the catapult and refreeze itself, instead of destroying it. You'll never need to switch transforms.

If you have the camera aimed at the catapult to begin with, and your code switches to bullets as you spawn them, have the bullet script do the same thing, but in reverse. Something like: GameObject.Find("MainCamera").GetComponenent("SmoothFollow").Target = GameObject.Find("catapult").transform;

Either way, you can also do something in smoothFollow like:

if (target is moving) put camera behind it aiming the way it moves
else put camera over it