[EricH]

All of them...

Given that your shooter can move in 2 directions (is it one pivot changing position, or is it two separate motions?), what do you want to do with it? Auto-aim is best done with a camera and some form of potentiometer, in general; there are a number of other sensors that could assist in loading, finding the endpoint of motion, and other tasks.

In short, your question is very broad to get a useful response. What exactly do you want to do?