I would agree that although you can use the hardcast for thinskined animals like deer, if I had a choice, I would prefer to use an expanding bullet.
I have some Oregon Trail 240 gr SWC's loaded up for my 4 inch Mountain Gun, but that is basically for a hog backup gun. It is an extremely hard solid, that would do little more than drill a hole, unless I hit something solid with it. Of course, If that hole is drilled through the vitals, it will do it's job, it just comes down to how long that will take.
Kevin