Odd to be discussing AR-15s/M-16s here, but...most of the newer versions (and all the clones) have a feature that projects out from the upper receiver behind the ejection port (a port buffer?) that deflects the brass away from the face of a left-handed shooter. I carried mine on a job many years ago and this feature wasn't commonly available then (early 1980s)....
That feature is the brass deflector, which was added (IIRC, beginning in the late 70s for issue weapons) to the later M16A1 and all subsequent A's. It was added specifically to address lefties' problems with brass in their faces and in their shirts.
