One of the main advantages of the 350 Legend upper is that it can easily fit onto standard AR-15 lower receivers. This means you can swap out your current upper without needing a new lower. This feature makes it quick and simple to change calibers based on your shooting needs.One of the main advantages of the 350 Legend upper is that it can easily fit onto standard AR-15 lower receivers. This means you can swap out your current upper without needing a new lower. This feature makes it quick and simple to change calibers based on your shooting needs.