The LE6940 and LE6945 Upper Receiver Groups offer and upgrade over the traditional M4 setup. The LE6940 features Colt's monolithic upper receiver, which provides a one piece Picatinny top rail and rigid mounting surfaces all around, in addition to a completely free floated barrel. Built-in flip-up front sight is compatible with most standard height rear sights. Available with 16" or 10.3" chrome lined, 1-7 twist, button rifled barrel. Available with or without a charging handle, bolt carrier group, and back up sights. All NFA rules apply. Mfg: Colt