NFA Registered machineguns are expensive. The cheapest you can get is a MAC-11, but MAC-11s are uncontrollable bullet-hoses. Lage Manufacturing stepped in to offer an AR-15 style upper for 5.56x45mm, thereby converting full-auto MACs into a more controllable platform.
It's still incredibly cursed, though.
Changelog
V1.0.0 -- Initial Release