Everything you need to convert your existing upper to a dedicated .22LR. Just purchase a magazine and you are ready to go. For best performance use a round style hammer as notched hammers can cause function issues and 36 grain plated nose bullets have proven to be the best choice for function.
CMMG 22D5B6E Replacement Barrel Kit with Bolt Carrier Group, 22 LR 4.50″ Threaded, Black Nitride Chromoly Steel, Fits AR-15/Mk4