LR-308 uppers are not as simple as AR-15 uppers. There are a number of standards. My LR-308 Super Lowers are designed to use the LR-308 / DPMS standard. Unfortunately, not all companies properly name their uppers, so care is needed. Bear Creek Arsenal, Aero Precising, and KAK all make LR-308 uppers that will work with my lowers. Bear Creek incorrectly calls them AR-10, and Aero calls theirs M5. True AR-10 uppers will not work. Below is a more in depth video.