Calculating electrical contact surface area
This is a fairly sophisticated contact resistance problem. If I understand, the ball will be making the electrical contact. A sphere has very poor surface mating against a flat. That being said, we make high voltage/high current relays up to several hundred amps and the moving contact is made from rod stock. Similar to a sphere but more contact area.

With a 1" diameter x 1/2" length we get 200A continuous and about 5000A momentary. The spring return is less than 9oz but the contact PSI is probalby very high.  I'm not sure how to relate the 2 surfaces.