Cut the inside of the reflector shield

1. Start the BooleanDifference command.

2. At the Select first set of surfaces... prompt, select the flashlight body, and press Enter.

3. At the Select second set of surfaces... prompt, select the new truncated cone, and press Enter.

   

4. Drag with the right mouse button held down to rotate the view in the Perspective viewport a bit so you can see inside the flashlight.