Summary

I used ammomikes idea but showed how to connect a sensor to his speed controller.
I added a separate adjustable sensor holder . Everyone is printing the sensor holder to the drop tube feeder. Your drop tube (from bullet feeder to die) will be pulled through the sensor holder. This will allow you to adjust your distance and bullet capacity instead of having the sensor attached to the bullet tube.
I found a cheaper compact sensor and provided the wiring.
The sensor might help out more projects you might have.
Caveat: Please discuss with a licensed electrical technician before playing with electricity.