I've got an ar with a colt upper, plum crazy lower, and a s&w barrel chambered in 5.56. Today was the first time I've tried shooting it. I got some tulammo 55grain from Walmart lastnight. The problem is that it won't eject a round after being fired. It has the m16 bcg. When you rack the slide it'll eject and pick up the next round out of my colt 30 round mag. Any idea what I should do to fix this?