A very talented builder over at AR15.com is constructing his very own Magpul Folding Machine Gun (FMG9). Using an airsoft platform, a Glock slide, a nine inch barrel and a mill, “RDTCU” was able to build a fully functional PDW. I’ll let his details and pictures speak for themselves:

Finally had some time to work on [the FMG], should be getting close to a test fire, maybe in the next couple weeks.

Magpul PTS shell/frame
G17 slide
Lone Wolf 9″ barrel, shortened
Polymer80 front locking block, lugs welded up and re-profiled
Standard Glock trigger/sear assembly in a steel rear insert
Trigger bar welded up and re-profiled for the folding trigger

Working on a stronger carry handle from a chunk of leftover delrin, already slotted it to slide on the rail. It will still come off easily but will have have better sights than the little nubs on the original and will have an integral light instead of using a separate rail-mounted one. It’s way too tall right now, the finished product will be much shorter.

As a reminder, Wikipedia has a brief history of the FMG9:

The Magpul FMG-9 is a prototype for a new generation of folding submachine guns, designed by Magpul Industries in 2008. Like other folding machine guns, it would be used for concealed carry and can be disguised as anything from a small package to an extra laptop battery. It is made out of a light-weight polymer material rather than metal, making it very light and easy to carry. It is also small enough even to fit in the back pocket of most everyday pants. It was developed for potential use by personal protection details such as the United States Secret Service. As of 2014 Magpul has indicated no intention of bringing the prototype to production.

Magpul FMG9 on Ultimate Weapons: