Aero Precision is now offering complete uppers build around their very cool M4E1 upper receivers. There are currently 2 configurations available but you can expect more in the future.
The M4E1 Upper Receivers are designed from the ground up to accept proprietary free float rails. They have a large collar that is actually integrated into the upper that accepts the free float rail rather than a separate barrel nut. This creates a very rigid interface between the rail and the receiver and makes assembly a breeze.
Previously, these uppers were only available in stripped form. Now they are available in complete form; ready to drop on a lower and go. Check out the available M4E1 Uppers at Aero Precision.