Pro 1000 Case Sensor Explanation

The case sensor on the Pro 1000 prevents the primer pin from retracting down far enough so a primer can slide on top (or is supposed to).  If you are getting primers when no case is present, the pin must be retracting even though the case sensor hasn't been tripped. 

Check to make sure that the straight end of the case sensor spring is in the slot next to the primer pin in the shell plate carrier.  Also make sure that the pivot screw for the case sensor is not over tightened, causing the case sensor to bind, and that the case sensor is assembled correctly.  The steel bushing should be installed so the small diameter goes through the case sensor.