I saw someone doing this at the range so I tried it myself and thought I'd pass it along. I used this at an indoor range to keep 223 brass from bouncing all over the place.

Take a hand towel and pull a few it through the carry handle so you have it draped say down to the magazine on the left side with the bulk of the towel draped on the right over the ejection port. Blast away and the towel will slow down the brass. Cases seem to clear the weapon OK, only problem I noticed is that the brass stays hot a lot longer.

Looks a little silly but most folks don't laugh at shooters holding an AR-15. [:D]