This is a Diemaco M16-LMG RO750 upper receiver assembly on a Colt's Mfg preban Match HBAR 6550 AR15 semi-automatic rifle lower receiver. Also included is the original hydraulic buffer and proper return spring. Rifle is chambered for 5.56 NATO (.223) and feeds from STANAG magazines. Both halves are used, in good shape, fully functional, and both date back to the early 1990s. So they matchup well together to form an authentic civilian legal version of this interesting AR15 variant. Rifle comes with 1 Colt marked magazine and Colt manual with lock