Think Sten!
I was thinking of something like this.
The Government even puts out a little book on how to set it up and use it. See FM 23-91 and FM 23-91A
With one of those mounted in the back of the old Pick Up Truck, ice fishing would be a lot easier.
Or Grease Gun or PePeSha.
Barrels on the Stens or M3s would tend to be short because all one would have to work with would be repurposed handgun barrels. The advantage of the PPSh would be that any 30 cal. barrel could be cut down to the desired length and re-chambered to work with 7.62x25 ammo. They could make a longer barreled, more effective weapon.
Of course, we are law abiding folk and nobody here would never want to do something like this.