Copy the reflector shield cone
You will now copy the truncated cone to create another truncated cone that will be used to cut the inside shape of the reflector shield.
Turn off the Center object snap.
Select the truncated cone.
Start the Copy command.
At the Point to copy from... prompt, in the Front viewport pick any point.
At the Point to copy to prompt, turn on Ortho and drag the cone to the right until the sides of the copy are inside the first cone.
Pick a point to place the copy, and press Enter.

Ortho will keep it moving in a straight line.

Join the two parts of the body together
Start the BooleanUnion command.
At the Select surfaces... prompt, select the cylinder.
At the Select surfaces... prompt, select the first truncated cone, and press Enter.
Not much appeared to happen, but the cylinder and the truncated cone are now one object.
