bushmaster chambers are tight.. add some extra tacky soot from shooting steel, and you'll get stuck cases. if you shoot alot, you will get stuck cases... gotta be able to address that on your own. apparently this is an addendum thread to a previous thread i haven't read, but if you get a stuck case/closed bolt, you can "mortar" the bolt back- sometimes extracting the case, and sometimes just tearing the rim off- by dropping the loaded mag, inserting an EMPTY mag (to hold the bolt open on return), and slamming the buttstock into the ground. concrete if you have a rubber buttpad, grass if it's plastic.
if the casing extracts, scrub the chamber and carry on. if the round doesn't extract, tap it out with a cleaning rod. if the head sheers off completely, you'll need a broken shell extractor- can usually be found online for less than $20, and should always be kept in the range bag for just such an event.
to prevent stuck cases from ever happening to begin with, get your chamber reamed with a quality 5.56 chamber reamer- i recommend the ned christianson reamer. you'll never have a stuck (non-broken) case again.