Yes its the Madbull one, nicely made, you need to drill through the bolt ring if you want to retain a dummy gas tube though.
Actually going for a bigger gun, aiming for a MK12 Mod 3 if you will, i notice Daniel Defense and BCM sell these and are in use in theatre.
Heres a mock up - need a higher scope mount and to sort the 18" barrel out properly.
Oh if anyone has a spare original MWS M4A1 barrel they dont want please DM me