Looking for advice on how to turn off a motor when there is an item blocking a sensor. I found an inductive proximity sensor that I think could work. I am trying to make a brass case annealer similar to this one
What you are looking for is a normally closed relay which is sometimes abbreviated as NC relay. You should place the relay in you circuit so that switch side has the ability to interrupt the motor when the sensor is tripped. Here is a possible schematic of how your circuit could work.
When an object is placed in front of the sensor it closes the sensor which opens the relay which cuts power to the motor. This is one way to achieve control of your motor when an object is placed in front of the sensor.