ATC up and running but the bits fall down

[RobLM]

EDIT: just discovered a better thread for this topic:

Altmill spindle ER16 collet nut - when ER16A isn't ER16A?

I purchased a couple of dozen ER16A collet nuts earlier this week, for use on my new Altmill CNC router with RapidChange ATC. They came today, and the Haas nuts don’t fit - the Haas nut threads are a mm or more larger diameter than the spindle, and the nut itself is physically larger than the Sienci one. The Haas ER16 collets themselves that I also purchased are the same size as those supplied by Sienci, and fit in both nuts… I am surprised - I was unaware that there were multiple sizes of ER…

I got the Rapid Change ATC, and though figuring it out was a challenge, not plug and play like my Altmill and my Vortex, still I got it to work. It will make some jobs flow smoother.
Still one issue:
Some of my bits stick in their spring collets, but some of them slide right out.
Can anyone tell a success story I might emulate?