The FrankenSTEN
Dr. Will Dabbs over at Small Arms Review has a very interesting article up about the FrankenSTEN: a newly constructed 9mm upper receiver that mounts on an M16 lower receiver and allows selective-fire from a side-mounted 32-round STEN magazine.
The FrankenSTEN utilizes the factory barrel, magazine housing, magazine, and ejector from a Mark III STEN gun as well as a highly modified STEN gun bolt. The bolt requires the most redesign and machine work as the original STEN is an open-bolt gun with a fixed firing pin whereas the FrankenSTEN utilizes a closed bolt with a floating firing pin and the hammer and trigger assembly from the M16 lower receiver.
Images sourced from Blue Four Alpha