Fired a round, bolt pulled the casing out and was ejected halfway out the port but was caught between the next round, that had partially fed into the chamber, and I guess the top inside of the upper receiver.  Anybody had this happen to them before?  What causes this?  It only happened this one time (today) with about 400 rounds through it.  This was some 62 gr. British ammo that has RDRG and the Nato cross on it.