The amazing 5.7 AR15
This guide details the installation of the AR-57 upper receiver onto a standard AR-15 lower receiver, enabling the use of the 5.7x28mm cartridge. It also covers a practical modification using a Magpul PMAG as a brass catcher, demonstrating how spent casings are ejected downward through the AR-15's magazine well. The information is presented with high authority by Military Arms Channel, a recognized firearms reviewer.












