Piston sticking

I have some used pistons, I don't know the brand. They have a silver sleeve and the contact is a pointed metal piece that when pushed hits two thin contact plates. The contact plates are thin and flexible and are positioned like this /\. I have a few that are sticking. I tried cleaning all the contacts, used a small Emory board to clear the surfaces but they are still sticking. If you only press the piston until it first hits the contact youare ok, but if you push it all that was in (like you would do in the heat of battle) it will stick. Thoughts?