I was shooting this past weekend when my AR started have case extraction problems. It was working fine at first but after about 20 rounds the cases would not extract completely from the upper. The don't appear to be be getting stuck in the chamber.  The are getting pulled out of the chamber but end up laying freely in the bolt area.  If I chamber a round and extract it with the charging handle it seem to extract ok. It's only when I actually fire a round that the case does not come completely out of the gun.

Since I'm still new to working on the AR I was looking for any information before I take anything apart.

Thanks
Jonathan Craig