Working up loads on a non .223 AR recently in the rain and cold, I decided that it would be nice to have a brass catcher for the rifle and bought a $7 one that worked but not the best mounting system, so another $10 for a QD mount off of eBay and a 3/8 strip of 1/8" steel and I had found a use for a section of the rail and a brass catcher that mounts and unmounts quickly and is always lined up with the ejection port.