The C7 retro carry handle receiver has been very hard to get, so Potomac Armory and Charlie's has arranged for a special forging to be made and milled to meet the exacting requirements for M16E1 "Commando" and Gordon Carbine military clone builds, and for other retro enthusiasts.
The C7 upper receiver was a bit of a transitional model between the A1 and A2 production. This model upper receiver is an M16A1 upper, but with a shell deflector, which is typical of the A2 upper receiver. The C7 upper retains other A1 features, like the more simple rear sight.
photos courtesy of Potomac Armory, Administrative Results (YouTube), MeIoMelonSoda (Reddit)