Just swap this drop in conversion with the bolt carrier group from your 5.56/.223 chambered rifle and you will be ready to shoot .22LR. Ships with 25rd 22LR magazine. Compatible with left handed 5.56mm/.223 chambered upper receiver groups. Ships with 25rd 22LR magazine. 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.