Builder is unknown at the moment. The upper is Muller Industries out of Memphis. They made Colt's uppers for a long time. The barrel is an WYLDE cut 1/8 twist fluted 18" with an A-2 flash hider. The BCG is a full auto mil-spec. I bought these upper assemblies in a dealer lot of factory assembled uppers.
"The Wylde chamber has a shorter THROAT than a standard 5.56 chamber. Rifles shoot Extremely well with the bullet closer to the LANDS of the rifling."