The website aim arms is a one-stop-shop AR15 Complete Premium Upper Receiver to get all the premium parts of the rifle that are not readily available anywhere. It is always required to buy the premium parts with utmost care as each of them performs a massive role in the function of the rifle. Ensure that the website from which one buys such integral parts has the license to sell it and is marked by the manufacturing company. There is no alternative for the color of the features and the material. One should know the weight of the parts and the rifle as a whole.