Abstract: Casing catcher for AR-style rifle is an ammunition cartridge casing catcher, shell casing catcher, or brass catcher that is reversibly attachable to any AR-style rifle. Casing catcher for AR-style rifle uses a reversibly attachable means to magnetically reversibly attach to the inside surface of the ejection port cover on any AR-style rifle with a two key picatinny rail attachment system to reversibly align itself properly and attach itself to the AR-style rifle. Casing catcher for AR-style rifle has a cage, a magnetic weir plate, a lock pin receiver, a lock pin, a first key, and a second key. Magnetic weir plate has at least one magnet attached thereto. The first key to has a special shape or profile that includes a special right facing foot protuberance that is the inverse shape of the left side of the picatinny rail on any AR-style rifle.