Actually that rail is Geissele MK4 rail. Alright.. going to share it with you. Midway, Rainier and Brownells will be getting some Geissele 13" MK2 and MK4 rails. The MK1 which is more popular but way too backlogged. Also Geissele will be selling blemished ones for $50 off.
I hope i can snag some of them.. so i can build BCM Jack carbine "Clone" or even better. Lol