A concealed carrier takes down a rifleman.
We often hear this can't be done. Of course it can be done. It just can't always be done. If the guy walks in with his rifle and lights you up first thing, you aren't going to have a chance to do anything. But if he's there for something else, and you're careful not to be observed bringing your own weapon to bear, you have the advantage provided that you can hit your target. He's going to have to observe you, orient to what he's observing, and decide to shoot you before he can do it. If you're decisive, it's possible.