The King Arms officially licensed COLT M4A1 receiver set is made from only the best materials and manufacturing processes. By starting with high quality steel, these receivers are milled and machined to exacting standards. All of the accessories and parts that are included in this kit are also made from steel. Featuring the officially licensed iconic COLT trademarks and unique serial numbers laser engraved onto the lower receiver and a durable, wear-resistant finish, this receiver set looks and feels just like the real-steel gun parts! The picatinny/weaver upper rail is milled to perfectly mesh with M4 style free float RIS systems as well. At the back of the lower receiver, King Arms included a special channel for routing rear-wiring into a crane or other style stocks to prevent wire pinching. If you're looking to build your AEG and use only the best parts, this receiver set is a rock-solid start to a great build!