Ya lost me on the star thing. Are you talking about the bolt face?, that the round sits in. 
That is supposed to engage the barrel extension,
and on the last bit of bolt carrier movement, it rotates to lock it into place. As the bolt moves back, that bolt face rotates, unlocking it and then it will pull out of the barrel extension. If it didn’t want to rotate, then I would look real good at the teeth on the barrel half, to see if its got carbon on it. The carbon will get smashed flat from the bolt hitting it as it engages, and it will make the carbon look shiny like metal. Take a small screwdriver and very gently scrape the barrel area to see if carbon flakes off. That bolt should move in and out like butter, if not fix it or you will mess some stuff up when it gets worse and the 28,000 psi of operating pressure screws it up.
http://www.metacafe.com/watch/772751/how_a_m_16_bolt_works/ Great animation of the weapon cycling to see how it locks