Help with a ring launcher
A ferromagnetic ring will sit and vibrate at the AC cycle rate.  Pulsed DC is likely what you need.  Typically "washer launchers" are a big bank of capacitors with voltages in the kilo (kill-you) range that are triggered to dump and "fling the ring".  If you do not have the equipment to handle these measurement tasks, that is where you need to start.  Get the test equipment.

For non-ferromagnetic, but conductive, rings, you sound like you're on the right track.

There is a physics youtube channel that has a "launcher" of the sorts that is sounds like you are talking about.  They use room temperature [Al] and test, then the same ring Liquid[N] cooled. 

Keep in mind the device in this video uses UK line voltage.

The Electric Cannon