I had this happen when during Wolf torture tests on my first AR build. Sometimes they get so stuck that the pogo method just rips off the rim of the casing.
If that happens, your bolt will be free, lock it to the rear. Then get a cleaning rod and tap it out. Make sure the cleaning rod is inside the spent casing and not resting on the "lip" to avoid damage to your bore. Then tap it out with a small hammer or such.