Airsoft GI Uncut has a quick video of the Knight's Armament M4 CQB URX 3.1 AEG done by GI Michael... "The Knight's Armament URX 3.1 OEM'd by G&P is another edition of performance rifles from ZShot. Externally, the upper and lower receiver are made out of an aluminum alloy for increased durability without increasing the overall weight. Towards the front of the upper receiver is a licensed URX 3.1 rail.