Why stop adding one more Gauss Gun to your monster Gauss Gun set, because you've starting to smash the Neodymium Magnets?
Just build this Project;
As the magnet isn't touched by the roller balls, there are no speed or force limits!
And to re-set it, just push the spheres forward, no hassle!
It has it's dimensions set for a 12.7 mm Neo, but you can buy any size, draw a square into the plans, as a template, and scale it until it fits the plan's square.