[bncsauve]

Sort of sounds like you aren't getting the ball locking mechanism released. The ones with the sliding buttons are pretty self explainatory, but, the ones with the collars can be deceiving. On mine, you don't slide the collar, but instead, pull in on the face. It's not really intuitive. I've stood there, sliding the collar until I was blue in the face until I finally remembered to pull on the face and it then goes right on.