I don't have time to dig the rifle out right now but will do when I get a moment.

Meanwhile, an explanation of how the seater works:.

Extend the case forward and drop a bullet in the end.

With the tool completely flat, slide the case into the chamber.  

Push on the end of the handle to drive the bullet out of the case and as far into the chamber as possible

Lift up on the handle to seat the bullet.

In answer to your question, the two legs on the aluminum part drop down into the mortise in front of the hammer, providing the camming action.  This is probably most easily seen in the last photo.