Colt M4 upper receiver.
This high-end receiver has the M4 16.1 inch barrel with removable flash hider, bayonet lug, double handguard, flat top receiver, and all internal parts. All parts are properly marked with Colt’s ID markings. This receiver was not put together from a kit (one complete unit from the factory). The carry handle and side sling mount are not included (I did not use them/sold) This receiver had approximately 500 rounds fired through it and it looks like new.
I can email pictures if requested.