I added a picatinny rail mount to a friend's AR so he can mount a Caldwell brass catcher to it and easily recovery his brass. .223/5.56 brass is pretty easy to find at the range, but he wants to recover and use the brass fired from his gun. I think he's going to convert some to .300 Blackout. I got to use my MTM Gun Vise for the first time, too, while putting on the mount.