This Madbull Noveske Upper Receiver allows you to customize your CA M15 so it doesn’t appear as if every other M4 out there. Madbull made these upper receivers to match up with their Novekse free float rail, but it’s great with the other M4 front . This piece is merely compatible with the Old Syle Classic Army Lower Metal Body. you’ll tell if you’ve got an old one if you’ve got 2 pins, one left and one right, protruding of the rear of your upper receiver that’s alleged to line up with 2 holes in your lower receiver. this is often an excellent aesthetic upgrade with or without the Noveske Rail.