Purchasing a factory AR-15/MSR certainly satisfies your need for instant gratification. Perhaps you are new to the black rifle world and intimidated by the seemingly never-ending array of choices on lowers, uppers and parts that buying stock just seems easier. However, building your own AR-15 rifle satisfies in the long term. To start, you will need a lower receiver. The lower receiver is the part of the gun that makes it a gun and comes with a serial number. For your first entry-lever AR-15 build, the Del-Ton stripped lower will handle hundreds of thousands of rounds.