I jbwelded a flat washer to the underside of the ‘button’ in which a small diameter wire coiled spring just barely fits inside of the hole. I added a second smaller spring (inside if the first) to make it a little more positive. Jbweld is your friend.
In thinking about my next version ‘charger’ I’m wondering if a couple of small coiled springs could be used inside of the unit to propel a teflon follower to push the rounds out of the charger.