Barret is offering uppers to convert your Model 82A1 series rifle (top) from one caliber to the next. I can't picture any reason you'd need to switch from a .50 BMG to a .416 Barrett but, by golly, you can if you want to. (As a side note I've shot this rifle in .416 Barrett--suppressed, no less--and pulling the charging handle back on this beast is a near religious experience. When that bolt slams forward putting a shell into battery it is like you're arming the Fist of God. There's no surer sign that something downrange is about to experience a world of hurt.)